Classical Mechanics Lecture 1: 1-D Kinematics In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996

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1 Classical Mechanics Lecture 1: 1-D Kinematics In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 1, Slide 1

2 Demo: Inclined Plane w/ Lights and Bowling Ball Inclined Plane with Lights and Bowling Ball Lights on the side of a ramp are placed so that their distance from the starting point of a ball rolling down the ramp is proportional to the square of the time from when the ball is released. The lights are all flashed at a frequency determined by the angle of inclination so that the lights flash when the ball passes over each light. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 1, Slide 2

3 Classical Mechanics Lecture 2: Vectors and 2-D Kinematics In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 2, Slide 1

4 Demo: Cannon on Cart with Tunnel and Pulley Cannon on Cart with Tunnel (with pulley option) A cart is given a push on a horizontal track and let go. A steel ball inside its cup is launched straight up by a spring that is triggered at a certain point on the track. The ball demonstrates independence of X-Y motion by landing back into the cup on the moving cart. Due to this X-Y independence, the ball can jump over a tunnel placed at an appropriate spot on the track. A pulley can also be used to accelerate the cart. Using this option, the cart will be going faster than the ball, and the ball will not land in the cup. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 1, Slide 2

5 Demo: Shoot the Monkey Shoot the monkey A stuffed monkey, "Zip", is shot by a dart aimed directly at him from an air gun. Even though he tries to avoid the dart by jumping from his tree at the moment that the dart is launched, Zip gets hit. This demonstrates the X-Y independence of the dart's and the monkey's motion. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 1, Slide 3

6 Demo: Independence of X-Y Motion Independence of X-Y Motion (Two Ball Drop) There are two small steel balls on a platform. When the system is triggered, one ball falls straight down while the other is projected horizontally with a loaded spring. Each one hits a carefully pre-positioned metal plate, so that when they hit, there is a distinct "clink" that the audience can hear. As can be heard, the two balls hit at the same time, and this shows that the X and Y components of motion are independent of each other. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 2, Slide 4

7 Classical Mechanics Lecture 3: Relative and Circular Motion In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 3, Slide 1

8 Demo: Tractor on a Moving Sheet of Paper Tractor on a Moving Sheet of Paper The battery powered tractor moves along on a sheet of paper or cardboard. It can be shown that the tractor's motion relative to the paper or cardboard does not vary as the paper or cardboard is moved. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 3, Slide 2

9 Demo: Tennis ball on a string with rod Tennis Ball on a String with Tube Begin by spinning the tennis ball on the string in a circle pattern. The radius of the ball's circular path is decreased by slowly pulling on the string from the bottom of the tube. As a result, the ball's angular speed increases in order to conserve angular momentum. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 3, Slide 3

10 Demo: Water in a Bucket Water in a Bucket Put some water in a bucket (fill about 1/4 full) and show that if the bucket is swung overhead in a circular path fast enough, the water will stay in the bucket. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 3, Slide 4

11 Demo: Wine Glass (cup) on Plate Wine Glass (cup) on Plate Holding the string by a hollow rod, swing the plate with the cup/wine glass on it in circles. Centripetal force will keep the glass on the plate. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 3, Slide 5

12 Classical Mechanics Lecture 4: Newton s Laws In-class Demos Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 4, Slide 1

13 Demo: Fire Extinguisher Cart Rocket Cart (Fire Extinguisher cart) The lecturer sits on the cart. The fire extinguisher is also attached to the cart, and then the pin is removed. The cart plus the lecturer as a system are propelled in the direction opposite the escaping gas. This demonstrates conservation of linear momentum. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 4, Slide 2

14 Demo: Table Cloth and Dishes Table Cloth and Dishes Dishes, a candle, and a pitcher are arranged on a table cloth. The lecturer pulls the cloth slowly at first, causing the dishes to move also. Then the cloth is jerked suddenly, leaving the dishes, candle, and pitcher on the table. This is a demonstration of Newton's First Law. Sometimes the lecturer has the class do a count-down or has a volunteer pull the cloth from under the objects. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 4, Slide 3

15 Demo: Fred the Bear Fred the Bear A bear on top of a cart (or Judy) collides with an obstacle. The cart stops but the bear falls forward due to its inertia. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 4, Slide 4

16 Demo: Bow and Arrow Bow and Arrow When we pull back on the bow, the resulting tension can be used to accelerate the arrow across the room. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 4, Slide 5

17 Demo: Rotating Al Plate & Dry Ice Pucks Rotating Aluminum Plate and Dry Ice Pucks on Red Stool A frictionless dry ice puck is given a push along the line drawn on the plate and then the plate is rotated. The puck moves in a straight line relative to the floor, but in a spiral relative to the frame of the rotating aluminum plate. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 4, Slide 6

18 Classical Mechanics Lecture 5: Forces and Free-Body Diagrams In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 5, Slide 1

19 Demo: Tug of War with Rope on Skateboards Tug of War with Rope on Skateboards Two people pull on opposite ends of a rope in a tug-of-war while also standing on skateboards. It can be observed that momentum is conserved by comparing their momentum changes. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 5, Slide 2

20 Demo: Horizontal Springs Horizontal Springs Various springs attached to a clamp are used to demonstrate properties of springs. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 5, Slide 3

21 Demo: Springs and Strings in Series in Parallel Springs and Strings in Series and in Parallel A mass is hung from two springs in series, then in parallel. The springs are stretched more when the mass is hung in series. Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 5, Slide 4

22 Demo: Scale on a Skate with Weight(s) Scale on Skate with Weight(s) A spring scale covered with a cloth is attached to a roller skate. The scale has one string attached to its support and another attached to its weighing hook. The support string is attached to a clamp and the other string goes over a pulley and has a hanging mass with weight W attached to it. Ask the students to guess what the scale will read, and then reveal the answer. The scale is covered again. Next, the support string is also fitted over a pulley, and an equal mass with weight W is hung from it. So there are W pounds pulling on the right, and W pounds pulling on the left. What does the scale read now? Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 5, Slide 5

23 Demo: Tug of War with Two Spring Scales Tug of War with Two Spring Scales Two spring scales that can be hooked together (for tug-of-war) [tension same no matter what (scales read the same)] Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 5, Slide 6

24 Classical Mechanics Lecture 6: Friction In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 6, Slide 1

25 Demo: Inclined Plane with Blocks Inclined Plane with Blocks (Static Friction) An adjustable ramp can be set at different degrees of inclination. A collection of wooden blocks with surfaces that have different coefficients of friction (sandpaper, waxed paper, etc.) are placed individually on the incline. When the ramp reaches the critical angle, gravity overcomes static friction and the block begins to slide. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 6, Slide 2

26 Demo: Static/Sliding Friction Demo Static/Sliding Friction Demo Static friction and sliding friction are compared using a sled containing lead bricks. The sled is pulled with the scale until the sled begins to move. The maximum force needed to overcome the static friction and begin the sled moving is noted. The sled is then pulled at a constant velocity and the kinetic friction measurement is noted. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 6, Slide 3

27 Demo: Inertia and the Bicycle Wheel Inertia and the Bicycle Wheel Lecture demo showing the different points of inertia with a bike wheel Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 6, Slide 4

28 Classical Mechanics Lecture 7: Work and Energy In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 7, Slide 1

29 Demo: Timing of Three Falling Objects Timing of Three Falling Objects Three objects (racquetball on platform, bowling ball pendulum, and frictionless cart on a track) are allowed to fall the same vertical distance d, while motion sensors record the time it takes for each object to fall. These times should all be the same, since air resistance will be negligible. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 7, Slide 2

30 Demo: Suitcase with Rope and Scale Suitcase with Rope and Scale One end of a 100 N spring scale is attached to a string, and the other end is attached to a wooden block (suitcase), which can be pulled across the floor by the string as the scale measures the applied force. With this setup, the lecturer can demonstrate the difference between static and kinetic friction, and their numerical values. This demo cannot be done on the lecture room floor the way it currently is. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 7, Slide 3

31 Classical Mechanics Lecture 8: Conservative Forces and Potential Energy In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 8, Slide 1

32 Demo: Masses on Various Springs Masses on Various Springs Various weights are attached to the ends of various springs and the resulting oscillatory motion is observed. The lecturer can then ask the students about how various properties of the springs/masses (spring constant, spring length, mass, etc.) affect various properties of the wave motion (amplitude, period, etc.). Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 8, Slide 2

33 Demo: Dry Ice Puck Spring Shot Dry Ice Puck Spring Shot (conservation of energy) A spring with a known spring constant is used to shoot a dry ice puck along a track. The puck's final velocity is measured to demonstrate conservation of energy, since all of the spring potential energy (at the beginning) is converted to kinetic energy (at the end). Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 8, Slide 3

34 Demo: Bowling Ball Pendulum Bowling Ball Pendulum (conservation of energy) A bowling ball, suspended from the ceiling, is pulled back towards the wall and should touch the nose of the lecturer. Once released, the ball will swing back and forth. The lecturer remains in the same position unscathed upon the ball s return to the starting position. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 8, Slide 4

35 Classical Mechanics Lecture 9: Work and Potential Energy, P2 In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 9, Slide 1

36 Demo: Roller Coaster Roller Coaster Potential energy is converted to kinetic energy as the car rolls down the track. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 9, Slide 2

37 Demo: Cork Popper Cork Popper The shaft of an electric motor is connected to a cylindrical chamber lined with leather. A drop of water is placed in the chamber, and then it is corked. When the motor is turned on, the resulting work done by friction is converted into heat energy, heating the water until it evaporates. As the water vapor heats up further, it expands and exerts more pressure on the cork until the cork finally pops. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 9, Slide 3

38 Classical Mechanics Lecture 10: Center of Mass In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 10, Slide 1

39 Demo: Connected Masses spin on ice table Connected Masses spin on ice table Two masses are connected, and the center of mass is marked. When the lecturer gives the system a push, the two masses move in such a way that the center of mass can be seen to move with constant linear velocity. Mass can be added to one side to change the center of mass. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 10, Slide 2

40 Demo: Two Pucks on Ice Table; Rotating/Sliding Two Pucks on Ice Table; One Rotating, One Sliding Two identical pucks are pulled along a frictionless table. One puck has a string attached to its center; the other has a string wrapped around it. The strings run over pulleys and are attached to weights. When released, the weights pull the pucks with the same linear acceleration, regardless of where the strings are attached. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 10, Slide 3

41 Demo: Rubber Pork Chop Rubber Pork Chop The painted white dot shows where the center of mass of the pork chop is. The pork chop is thrown and students observe the parabolic behavior of its center of mass, no matter how the chop is thrown. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 10, Slide 4

42 Classical Mechanics Lecture 11: Conservation of Momentum In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 11, Slide 1

43 Demo: Inelastic Collision on Air Track Inelastic Collision on Air Track An object is sent along the air track at a given velocity. It collides with another object further along the track. The two then stick together and continue along the track together, showing an example of an inelastic collision. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 11, Slide 2

44 Demo: Ballistic Pendulum w/ clay ball and block Ballistic Pendulum with clay ball and block A clay ball is thrown at the side of a block which is covered in nails. The ball sticks and, due to conservation of momentum, the ball and box swing together in the direction that the ball was originally going. The amplitude of the resulting oscillation is measured and used to calculate the original speed of the clay ball. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 11, Slide 3

45 Demo: Happy Ball and Sad Ball Happy Ball and Sad Ball Both balls are dropped. Upon hitting the floor, one bounces and the other does not, due to the different coefficients of restitution of their materials. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 11, Slide 4

46 Demo: Super/Clayball Pendulum Block of Wood Super/Clayball Pendulum with Block of Wood We have two pendula, one of clay, and one with a super ball. Each one is pulled back to the same height, and let to hit a block of wood which stands on the table. The superball bounces back higher, so the momentum that it transfers to the block is greater than in the case of the clay ball. Thus, the block that the superball hits will fall down while the other block will remain standing. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 11, Slide 5

47 Classical Mechanics Lecture 12: Elastic Collisions In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 12, Slide 1

48 Demo: Elastic Collision on Air Track Elastic Collision on Air Track Two carts on an air track collide head-on and each moves in the opposite direction from which it came, showing the students a simple example of an elastic collision. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 12, Slide 2

49 Demo: Newton's Cradle Newton's Cradle The lecturer usually begins by taking one ball, raising it away from the others, and then releasing it to collide with its neighbor. The momentum of the ball is transferred through the system, and the ball on the other end reacts accordingly. The lecturer can then repeat the process with two balls, or three, or four. This demonstrates conservation of momentum in a collision involving several bodies. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 12, Slide 3

50 Demo: Glancing Collisions Glancing Collisions Two magnetic, frictionless (dry ice) pucks are pushed towards each other, while on the gridded table, to cause an elastic or inelastic collision. The lecturer can show how the different incident angles can affect the final trajectories. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 12, Slide 4

51 Classical Mechanics Lecture 13: Collisions, Impulse and Reference Frames In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 13, Slide 1

52 Demo: Basketball Drop with Small Ball on Top Basketball Drop with Small Ball on Top When a basketball is dropped alone, it bounces a certain height. When a smaller ball is dropped alone, it bounces a certain height. If the smaller ball is placed on top of the basketball, and they are dropped simultaneously, the small ball bounces significantly higher than it would if dropped alone. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 13, Slide 2

53 Demo: Basketball Drop with Small Ball on Top Basketball Drop with Small Ball on Top When a basketball is dropped alone, it bounces a certain height. When a smaller ball is dropped alone, it bounces a certain height. If the smaller ball is placed on top of the basketball, and they are dropped simultaneously, the small ball bounces significantly higher than it would if dropped alone. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 13, Slide 2

54 Demo: Collision of Bowling Ball and Golf Ball Pendula Collision of Bowling Ball and Golf Ball Pendula Students observe the collision of a comparatively small mass (the golf ball) with a large mass (the bowling ball) to see how linear momentum is conserved. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 13, Slide 3

55 Demo: Bed Sheet with Raw Eggs Bed Sheet with Raw Eggs When we throw an egg against a held sheet, the momentum of the egg is reversed by the force on the egg by the sheet, but the sheet 'softens the blow' in that the force takes place over a longer period of time than if the egg were to be thrown at a heavy and rigid fixed object like the wall or the floor. Because the collision is longer in duration, the maximum force applied to the egg is small enough that the egg does not break. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 13, Slide 4

56 Demo: Rubber Pork Chop Rubber Pork Chop The painted white dot shows where the center of mass of the pork chop is. The pork chop is thrown and students observe the parabolic behavior of its center of mass, no matter how the chop is thrown. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 13, Slide 5

57 Demo: Ball Bearings Drop Ball Bearings Drop A metal tube is filled with 228 ball bearings, and then the tube is tipped such that they are dropped from above a scale. When they hit the scale's platform, the average weight registered on the scale is a measure of the pressure exerted on it by the falling ball bearings. This is a large-scale model of what happens when pressure is caused by individual molecules hitting the walls of a container. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 13, Slide 6

58 Classical Mechanics Lecture 14: Rotational Kinematics and Moment of Inertia In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 14, Slide 1

59 Demo: Inertia Rods Inertia Rods One of these rods has most of its mass in the center, and the other one has most of its mass out at a larger radius. Hence, the first rod will have a smaller moment of inertia about its perpendicular axis, and it will take less torque in order to rotate it. The students should take turns feeling this effect for themselves. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 14, Slide 2

60 Demo: Phasor Wheel Phasor Wheel Magnetic arrows are placed on a round blackboard, which is hung vertically and then spun. This can be used to represent the direction of the instantaneous velocities and accelerations at various points on the circle. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 14, Slide 3

61 Demo: Different Weights on Rotating Stool Different Weights on Rotating Stool The lecturer (or a volunteer) sits on the spinning stool. With the weights (one in each hand), the person can change their moment of inertia. If they hold the weights with arms fully extended, they have a large moment of inertia, and will rotate slowly. If they bring the weights in towards the center, they reduce the moment of inertia, and begin to rotate faster due to conservation of angular momentum. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 14, Slide 4

62 Demo: Tennis Racket and Ball Collision Tennis Racket and Ball Collision An example of an imperfect elastic collision. No macroscopic collision is perfectly elastic. Although the shapes of the tennis ball and racquet are apparently restored after the ball is dropped on the racquet held fixed, the ball won't rise to the same height from which it was dropped. This shows that energy was not conserved in the collision and so the collision was not perfectly elastic Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 14, Slide 5

63 Hula Hoop with Arrow Demo: Hula Hoop with Arrow Visual aids used to show the direction of current. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 14, Slide 6

64 Classical Mechanics Lecture 15: Parallel Axis Theorem and Torque In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 15, Slide 1

65 Demo: Roll Different Objects Down Incline Plane Roll Different Objects Down Incline Plane The lecturer rolls a variety of objects down the incline plane, allowing for the comparison of angular accelerations. The students can see which properties (mass, radius, moment of inertia) affect these accelerations by "racing" similar objects down the incline. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 15, Slide 2

66 Big Wrench and Stuck Bolts Demo: Big Wrench and Stuck Bolts The longer the lever (handle on the wrench), the easier it will be to loosen the bolts and to apply the same torque. This is because torque is equal to (length of wrench) x (force applied). Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 15, Slide 3

67 Hula Hoop with Arrow Demo: Hula Hoop with Arrow Visual aids used to show the direction of current. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 15, Slide 4

68 Demo: Rubber Pork Chop Rubber Pork Chop The painted white dot shows where the center of mass of the pork chop is. The pork chop is thrown and students observe the parabolic behavior of its center of mass, no matter how the chop is thrown. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 15, Slide 5

69 Inertia and Bicycle Wheel Demo: Inertia and Bicycle Wheel Lecture demo showing the different points of inertia with a bike wheel Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 15, Slide 6

70 Classical Mechanics Lecture 16: Rotational Dynamics In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 16, Slide 1

71 Demo: Roll Different Objects Down Incline Plane Roll Different Objects Down Incline Plane Two carts on an air track collide head-on and each moves in the opposite direction from which it came, showing the students a simple example of an elastic collision. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 16, Slide 2

72 Demo: Atwood s Machine: Weight and Pulley Atwood s Machine: Weight and Pulley The Atwood's Machine consists of masses which hang on pulleys. A string on a given pulley will always have the same tension on each side. Hence, if we put the same mass on each side, they will not accelerate up or down. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 16, Slide 3

73 Demo: Sliding to Rolling Transition of a Bowling Ball Sliding to Rolling Transition of a Bowling Ball A bowling ball is slid along the floor and the motion detected by the motiondetector is displayed graphically on the computer. We can then use the resulting data to determine the speed at which the ball will begin to roll. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 16, Slide 4

74 Classical Mechanics Lecture 17: Rotational Statics: Part I In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 17, Slide 1

75 Demo: Suspended Static Beam Suspended Static Beam The beam is suspended from two scales which measure force. The lecturer can hang different objects from the hooks on the beam, to show how the net force/torque acting on the beam must equal zero. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 17, Slide 2

76 Demo: Static Truck on Incline Static Truck on Incline A truck on a 30 degree incline is held in static equilibrium by masses hung over two pulleys. After the lecturer pulls the incline out from under the truck, the truck does not move. This shows that the masses keep the system in static equilibrium. The sum of the external forces in both the X and the Y directions add up to zero. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 17, Slide 3

77 Classical Mechanics Lecture 18: Rotational Statics: Part II In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 18, Slide 1

78 Demo: Ladder Leaning Against Wall Ladder Leaning Against Wall A ladder, with wheels on both ends and a chain attaching its center to the blackboard, leans against the wall. When someone stands on the ladder, a scale on the wall measures the extra downward force of the person's weight. We can then compare to the measured weight using a bathroom scale (on the ground). Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 18, Slide 2

79 Demo: Floating Object (Static Equilibrium) Floating Object (Static Equilibrium) For equilibrium, the string force must be vertical since the only other forces, gravity and buoyant force, are also vertical. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 18, Slide 3

80 Solar System Model Demo: Solar System Model This is a model of the solar system and its orbits. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 18, Slide 4

81 Demo: Tweetie Eagle Tweetie Eagle The eagle is weighted such that it will balance on it's beak, due to its center of mass. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 18, Slide 5

82 Demo: Balancing Bottle and Block of Wood Balancing Bottle and Block of Wood A specially cut block of wood and a glass bottle are used to demonstrate the importance of finding center of mass. The wood alone will not stand on this slanted edge because the wood's center of mass is not supported by the base. The bottle is carefully placed in the hole in the wood. This new system of objects will balance because the center of mass of the system is now properly supported. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 18, Slide 6

83 Demo: Hammer on Hinged Board Hammer on Hinged Board For equilibrium, the string force must be vertical since the only other forces, gravity and buoyant force, are also vertical. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 18, Slide 7

84 Classical Mechanics Lecture 19: Angular Momentum In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 19, Slide 1

85 Demo: Drop Wheel Rim on Rotating Wheel Rim Drop Wheel Rim on Rotating Wheel Rim A car wheel rim is mounted on an axle. A similar rim is mounted above it but held up with a rope such that it does not come into contact with the lower rim. The lecturer spins the bottom wheel and times its period. The rope holding the top rim is then burned, causing it to fall onto the rotating rim. The new period is measured. The ratio of the moments of inertia can be calculated. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 19, Slide 2

86 Demo: Medicine Ball on Rotating Stool Medicine Ball on Rotating Stool The lecturer sits on the spinning stool. A volunteer hands the ball to the spinning lecturer. The lecturer holds the ball at arms length. The moment of inertia of the lecturer is increased when holding the ball, and so the stool turns more slowly. If the lecturer brings the ball closer, their moment of inertia decreases, and the stool rotates faster. This demonstrates conservation of angular momentum. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 19, Slide 3

87 Train on Bicycle Wheel Demo: Train on Bicycle Wheel Mount a track for a toy train onto a horizontal bicycle wheel, which is free to rotate. If we put the train onto the track and then run it with the motor, then the track/wheel combination will react by rotating in the opposite direction, thus conserving angular momentum. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 19, Slide 4

88 Demo: Different Weights on Rotating Stool Different Weights on Rotating Stool The lecturer (or a volunteer) sits on the spinning stool. With the weights (one in each hand), the person can change their moment of inertia. If they hold the weights with arms fully extended, they have a large moment of inertia, and will rotate slowly. If they bring the weights in towards the center, they reduce the moment of inertia, and begin to rotate faster due to conservation of angular momentum. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 19, Slide 5

89 Classical Mechanics Lecture 20: Angular Momentum Vector and Precession In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana- Champaign, 1996 Mechanics Lecture 20, Slide 1

90 Demo: Circular Ice Table with Hanging Weight Circular Ice Table with Hanging Weight Descrip)on: A large circular aluminum ice table with a rotatable pulley in the center allows a string to be a=ached from the dry ice puck to a mass (mass m) below. The lecturer rotates the puck (mass M) at a radius, r, and uses a Dmer to determine the velocity. (MV^2)/r for the puck can be compared to (m*g) for the different hanging masses. Demonstra@ons Dept. of Physics, Univ. of Illinois at Urbana- Champaign, 1996 Mechanics Lecture 20, Slide 2

91 Demo: Precession of Gyroscope using Bicycle Wheel Precession of Gyroscope using Bicycle Wheel Descrip)on: The bicycle wheel gyroscope appears to defy the laws of gravity as it balances on a single point (like shown). Begin with the wheel stadonary, hanging from the rope. Then as the lecturer rotates the wheel, it's axis of rotadon precesses, causing it to Dlt upwards. Demonstra@ons Dept. of Physics, Univ. of Illinois at Urbana- Champaign, 1996 Mechanics Lecture 20, Slide 3

92 Demo: Rotating Stool with Bicycle Wheel Rota)ng Stool with Bicycle Wheel Descrip)on: While the lecturer is spinning on the rotatable stool, a volunteer hands him/ her a rotadng bicycle wheel. Holding the wheel at different angles will either increase or decrease the angular velocity of the lecturer on the stool due to conservadon of angular momentum. The person on the stool can increase his/her velocity by handing off the spinning wheel to a stadonary person and then taking it back aser a full rotadon (the stadonary person flips the rotadng wheel over before handing it back to the person on the stool). Demonstra@ons Dept. of Physics, Univ. of Illinois at Urbana- Champaign, 1996 Mechanics Lecture 20, Slide 4

93 Demo: Different Weights on Rotating Stool Different Weights on Rota)ng Stool Descrip)on: The lecturer (or a volunteer) sits on the spinning stool. With the weights (one in each hand), the person can change their moment of inerda. If they hold the weights with arms fully extended, they have a large moment of inerda, and will rotate slowly. If they bring the weights in towards the center, they reduce the moment of inerda, and begin to rotate faster due to conservadon of angular momentum. Demonstra@ons Dept. of Physics, Univ. of Illinois at Urbana- Champaign, 1996 Mechanics Lecture 20, Slide 5

94 Demo: Gyroscopes Gyroscopes Descrip)on: Gyroscopes are used to demonstrate the modon (precession and nutadon) of the axis of a rotadng rigid body when a net torque is acdng on it. Demonstra@ons Dept. of Physics, Univ. of Illinois at Urbana- Champaign, 1996 Mechanics Lecture 20, Slide 6

95 Demo: Metersticks with Arrows Meters)cks with Arrows Descrip)on: Demonstrate electric fields with metersdcks with arrows Dept. of Physics, Univ. of Illinois at Urbana- Champaign, 1996 Mechanics Lecture 20, Slide 7

96 Classical Mechanics Lecture 21: Simple Harmonic Motion In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 21, Slide 1

97 Demo: Mass on Spring Mass on Spring Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 21, Slide 2

98 Demo: Bowling Ball Pendulum Bowling Ball Pendulum A bowling ball, suspended from the ceiling, is pulled back towards the wall and should touch the nose of the lecturer. Once released, the ball will swing back and forth. The lecturer remains in the same position unscathed upon the ball s return to the starting position. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 21, Slide 3

99 Demo: Simple Harmonic Motion Simple Harmonic Motion The harmonic oscillation of a spherical mass on a spring and the circular motion of a motor-driven mass are compared. The shadows on the screen move up and down in sync. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 21, Slide 4

100 Demo: Cart Attached to Inclined Track Cart Attached to Inclined Track When the cart is pulled down the ramp and released, it has a distancedependent force acting on it, which causes the system to exhibit simple harmonic motion. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 21, Slide 5

101 Classical Mechanics Lecture 22: Simple and Physical Pendula In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 22, Slide 1

102 Demo: Bowling Ball Pendulum Bowling Ball Pendulum A bowling ball, suspended from the ceiling, is pulled back towards the wall and should touch the nose of the lecturer. Once released, the ball will swing back and forth. The lecturer remains in the same position unscathed upon the ball s return to the starting position. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 22, Slide 2

103 Demo: Physical Pendulum Physical Pendulum This is an odd-shaped rigid body which can be suspended from different points along its edge. When it is displaced from its equilibrium position, it will oscillate back and forth. Then the lecturer can show that this method can be used to find the effective distance from the point of suspension to the center of mass. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 22, Slide 3

104 Demo: Physical Pendulum vs. Simple Pendulum Physical Pendulum vs. Simple Pendulum The beam is suspended from two scales which measure force. The lecturer can hang different objects from the hooks on the beam, to show how the net force/torque acting on the beam must equal zero. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 22, Slide 4

105 Demo: Torsion Pendulum Torsion Pendulum This is a torsion pendulum that has red spheres attached to it, to make the oscillations easier to see. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 22, Slide 5

106 Demo: Hula-Hoop Pendulum vs. Simple Pendulum Hula-Hoop Pendulum vs. Simple Pendulum The lecturer demonstrates that the hula-hoop pendulum behaves like a simple pendulum with a length equal to the diameter of the hula-hoop. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 22, Slide 6

107 Classical Mechanics Lecture 23: Harmonic Waves & Wave Equilibrium In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 23, Slide 1

108 Demo: Torsion Wave Machine Torsion Wave Machine Steel rods are evenly connected, at their centers, to a wire which is supported above a metal triangular base. When a rod, or group of rods, are displaced upwards or downwards, the wave propagates and then dies out. If there is a damper placed at one end, some of the initiated wave is reflected back. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 23, Slide 2

109 Demo: Transverse Wave on Rope Transverse Wave on Rope A truck on a 30 degree incline is held in static equilibrium by masses hung over two pulleys. After the lecturer pulls the incline out from under the truck, the truck does not move. This shows that the masses keep the system in static equilibrium. The sum of the external forces in both the X and the Y directions add up to zero. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 23, Slide 3

110 Demo: Transverse Wave Machine Transverse Wave Machine This hand-cranked apparatus can be set up so that its shadow is projected onto screen behind it. The apparatus shows a model of the movement of transverse waves and longitudinal waves, and shows their similar behavior. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 23, Slide 4

111 Classical Mechanics Lecture 24: Waves and Superposition In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 24, Slide 1

112 Standing Wave Machine Demo: Standing Wave Machine Produce a standing wave in a string by fixing one end, and then attaching the other to a mechanical vibrator. The lecturer can adjust the frequency such that clear nodes and antinodes can be seen by the class. Then, using the strobe light, show a "snapshot" of the standing wave at any point in time. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 24, Slide 2

113 Demo: Beat Frequencies Beat Frequencies The frequencies of the two function generators are adjusted so that you can hear clear beats from the interaction of the pitches that are coming from the speakers. The oscilloscope can be used to display the resultant waveform of the beats. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 24, Slide 3

114 Demo: Standing Waves on Long Spring Standing Waves on Long Spring An audience volunteer holds one end of the spring and the lecturer can set up different standing waves in the spring while the volunteer holds their end stationary. Alternate: Use a clamp and a pole instead of a volunteer. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 24, Slide 4

115 Demo: Wooden Whistle with Helium and Air Pump Wooden Whistle with Helium and Air Pump The densities of gases are shown with a wooden whistle. Helium from a tank and normal air from a pump are blown through a wooden whistle, one at a time. The sounds made by the different gases are compared. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 24, Slide 5

116 Classical Mechanics Lecture 25: Fluid Statics In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 1

117 Demo: Hydraulic Lift Model Hydraulic Lift Model Two syringes of different diameters are connected by plastic tubing. When the plunger of the larger diameter syringe is pushed a small distance, then the plunger of the smaller diameter syringe rises a larger distance. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 3

118 Demo: Pascal s Vases Pascal s Vases Several differently shaped vases are all connected at the bottom, and fluid is put into all of them. Since atmospheric pressure is the same in each vase, the fluids will seek their own level, no matter what the shape of the container. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 4

119 Demo: Density of Water vs. Alcohol Density of Water vs. Alcohol Ice floats in water because it is less dense than the water. In alcohol, however, the ice sinks due to its relatively greater density. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 5

120 Demo: Archimedes Principle Archimedes Principle 2 setups: one with the mass hanging from a double pan balance and the other with various masses hanging from a spring scale. In both cases, the weight of the hanging masses can be measured in air and then also when submerged in a beaker of water. The differences in the measurements give the buoyant forces of the water on the masses and can be compared to the weight of the water displaced by the respective masses. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 6

121 Demo: Floating and Sinking Pop Cans Floating and Sinking Pop Cans The diet pop floats while the regular sinks due to the difference in densities of the liquids. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 7

122 Magdeburg Hemispheres Demo: Magdeburg Hemispheres The Magdeburg Hemispheres fit together around the rim to form a sphere. There is a valve on one of the hemispheres. A vacuum pump is hooked up and the air is pumped out of the sphere. Since the atmospheric pressure is now so much greater than the pressure within, this pushes the hemispheres together, and it requires a very large force to pull the hemispheres apart. If the valve is opened, air rushes in, and they separate easily. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 8

123 Demo: Crush Tin Can with Vacuum Pump Crush Tin Can with Vacuum Pump A tin can is sealed and the air is pumped out of it with a vacuum pump. The can is then crushed by the atmospheric pressure pushing in on it. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 9

124 Surface Tension of Water Demo: Surface Tension of Water Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 25, Slide 10

125 Classical Mechanics Lecture 26: Fluid Dynamics In-class Demonstrations Demos Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 26, Slide 1

126 Demo: Charles Law Charles Law A glass jug (filled with air) is attached to a U-tube, which is filled with a bright yellow liquid (which will be easy to see by a large audience). Change the temperature of the air inside the jug by placing it first in a bath of cold water, and then in a bath of hot water. Notice how the volume of the air increases or decreases depending on temperature, by looking at the level of the liquid in the U-tube. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 26, Slide 2

127 Demo: Venturi Tubes Venturi Tubes This three tube model demonstrates the relation between flow speed and pressure. This can be observed by watching the levels of the liquid in the venturi tubes, and how it relates to the flow speed of the water in the larger tube. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 26, Slide 3

128 Demo: Head Pressure Demo Head Pressure Demo A tall tube has holes in it, equally spaced up and down the tube, but all aligned on one side. If we fill the tube with water and then let it drain out the holes, the flow rate at each hole will be different, due to the different pressure at each location. Thus, we can see that the water will shoot farthest out the bottom hole. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 26, Slide 4

129 Balance Objects on Air Jets Demo: Balance Objects on Air Jets This demonstration shows the importance of Bernoulli's Principle in keeping the ball from falling to the ground. The quickly moving air acts as a buoyant force on the ball, opposing gravity and keeping the ball stationary. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 26, Slide 5

130 Demo: Bernoulli s Pop Cans on Straws Bernoulli s Pop Cans on Straws Blow air through a straw in between cans and the cans are drawn together. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 26, Slide 7

131 Demo: Vacuum Cannon Vacuum Cannon Pressure differential between atmosphere and vacuum creates enough force to accelerate a ping pong ball thru the length of a tube to a speed high enough to pierce an empty soda can on impact. Demonstrations Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996 Mechanics Lecture 26, Slide 8