So what is motion? So what is motion? In math terms. What does speed mean? Some examples of speed: 60 miles/hour 100 meters/minute

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1 and Motion How is it moving? So what is motion? So what is motion? So what is motion? In math terms A change in position over time is the same as saying: How can we describe motion? Motion can be described by: DISTANCE (how far did it travel?) TIME (how long did it travel?) SPEED (how fast did it travel?) DIRECTION (which way did it go?) ACCELERATION (does the motion change?) What does speed mean? Some examples of speed: 60 miles/hour 100 meters/minute Let s break it down If you travel 60 miles per hour, how far do you travel in 1 hour? 60 miles/hour is the same as 60 miles 1 hour Let s practice calculating speed If you travel 100 km in 2 hours, what is your speed? Speed = Distance Time Distance = 100 km Time = 2 hours Speed = 100 km 2 h Speed = 50 km/h 1

2 Try it out! Time yourself moving across the 5 meter tracks on the floor. What is the DISTANCE? What is your TIME? Speed = Distance Time What is your SPEED? Speed, Distance & Time S D T Speed = Distance Time Time = Distance Speed Distance = Speed x Time Speed Practice Problems A family takes a car trip heading northeast from Durham, NC to Washington, DC. They travel for 4 hours and cover 360 km. What was their average speed? Speed = Distance Time = 360 km 4 h = 90 km/h Speed vs. Velocity SPEED tells you have fast or slow something is moving (changing position). Example = 25 km/h VELOCITY tells you speed AND DIRECTION! (changing position in a certain direction) Example = 25 km/h EAST Speed Practice Problems A family takes a car trip heading northeast from Durham, NC to Washington, DC. Their speed was 90 km/h. What was their VELOCITY? Velocity is SPEED and DIRECTION! Velocity = 90 km/h NORTHEAST Speed Practice Problems After school, your teacher went for a jog along Cornwallis Rd. She ran for 30 minutes at a speed of 150 m/min. How far did she run? S D T Distance = Speed x Time Distance = 150 m/min x 30 min Distance = 4500 meters (4.5 km) Speed Practice Problems Mr. Sawyer goes on a long bike ride in the country. He rides his bike 35 km at a speed of 20 km/h. For how long was he riding his bike? S D T Time = Distance Speed Time = 35 km 20 km/h = 1.75 h Acceleration Practice Problems Ms. Litwak buys a new car that can accelerate from rest (0 m/s) to 24 m/s in 8 seconds. What is the car s rate of acceleration? Final speed Initial Speed Acceleration = Time Acceleration = 24 m/s 0 m/s 8 s = 3 m/s 2 What was the average speed of the runner in the first 5 seconds of the race? Speed = 25 m 5 s Speed = 5 m/s 2

3 A snail slowly slithers down the sidewalk. It travels at a speed of 3 cm/min. How far would it travel in 20 minutes? Distance = Speed x Time Distance = 3 cm/min x 20 min Distance = 60 cm The fastest man on earth, Usain Bolt, runs at a speed of 10 m/s. How long would it take him to run 160 meters? Time = Distance Speed Time = 160 m 10 m/s Time = 16 seconds! Acceleration Acceleration Acceleration is a CHANGE in motion An object is accelerating if it is: Speeding up Slowing down Changing direction Using an Accelerometer An accelerometer measures acceleration. CAREFULLY push your accelerometer so it slides across the table and comes to rest. How does the paper clip show acceleration? In your notebook, complete the chart for each situation. Taking a ride on the school bus YOU act like an accelerometer when you ride the school bus. What happens to you, when the bus: Speeds up suddenly Turns a corner Stops quickly at a red light Rides along at a steady speed Taking a ride on the school bus When your MOTION CHANGES, that s a sign that the bus is ACCELERATING. Is it accelerating? Your car speeds up when the light turns green. A racecar goes at a constant speed around a curved track. A toy car moves in a straight line across the room at a steady speed of 0.5 m/s. A roller coaster car slows down as it climbs a hill. Graphing Acceleration On a position-time graph, changes in speed are shown by curved lines. Straight line Not accelerating! Curving up Speeding up Curving down Slowing down 3

4 Look carefully at each car below. Decide which car matches graphs A, B, and C. Graph B Constant Speed Calculating Acceleration Acceleration is the change in speed per unit of time. Acceleration = Final speed Initial Speed Time Calculating Acceleration A car leaving traffic changed its speed from 10 m/s to 25 m/s in 7.5 seconds. What was its acceleration? Acceleration = Final speed Initial Speed Time Graph C Accelerating Slowly Graph A Accelerating Quickly Acceleration is measured in units of meters per second per second, or m/s 2. Acceleration = 25 m/s 10m/s 7.5 s = 2.0 m/s 2 FORCES FORCES Introduction to FORCES When you ride a bike, your foot PUSHES against the pedal. The push makes the wheels of the bike move. When you drop something, it is PULLED to the ground by gravity. A FORCE is a PUSH or PULL in a particular DIRECTION. FORCES AFFECT HOW OBJECTS MOVE. s can affect motion in the following ways: They can make objects: BIG SCIENCE IDEA i) START MOVING ii) MOVE FASTER iii) MOVE SLOWER iv) STOP MOVING v) CHANGE DIRECTION vi) CHANGE SHAPE FORCES Identify each picture as a PUSH or a PULL. Is the force causing a change in speed or direction or both? FORCES Since forces cause changes in SPEED or DIRECTION of an object, we can say that forces change VELOCITY, so. FORCES More than one force can act on an object at one time. What happens to the object when forces act depends on 2 things: s cause ACCELERATION. 1) Strength of the s 2) Direction of the s 4

5 FORCES When 2 or more forces act on an object, the forces combine to form a net force. s may WORK TOGETHER or OPPOSE each other. FORCES If the forces cancel each other out, and do not cause the object to move, the forces are said to be BALANCED. If the forces don t cancel each other out 1 force is stronger than the others the forces are UNBALANCED and will cause a CHANGE IN MOTION. MEASURING FORCE The strength of a force is measured in NEWTONS. The symbol is (N). We use a SPRING SCALE to measure force. MEASURING FORCE - Always zero your balance before use. - Pull gently and with constant force. -Practice using your spring scale to drag items across your desk. COMBINING FORCES Two forces in the same direction can add together to produce a larger net force. 5 N right + = 5 N right 10 N right COMBINING FORCES Two forces in opposite directions can subtract to produce a smaller net force in the direction of the larger force. 5 N right - = 10 N left 5 N left COMBINING FORCES Two forces may cancel each other out (if equal and opposite) to produce NO NET FORCE. - = 0 N Circle the best answer: 1) The forces shown above are PUSHING / PULLING forces. 2) The forces shown above are WORKING TOGETHER / OPPOSITE FORCES. Circle the best answer: 7) The forces shown are PULLING / PUSHING forces. 8) The forces shown are WORKING TOGETHER / OPPOSITE FORCES. 5 N right 5 N left (No Net ) 3) The forces shown above are EQUAL / NOT EQUAL. 4) The forces DO / DO NOT balance each other. 5) The net force is 1000 N TO THE RIGHT / 1000 N TO THE LEFT / ZERO. 6) There IS / IS NO motion. 9) The forces shown are EQUAL / NOT EQUAL. 10) The forces DO / DO NOT balance each other. 11) The stronger force is pulling RIGHT / LEFT. 12) Motion is the to the RIGHT / LEFT. 5

6 50 N 4/25/ N 200 N 13) Two movers are trying to move a heavy box. One mover pushes to the right with a force of 150 N. The other mover pushes to the left with a force of 200 N. a) Draw & label the forces on the diagram. b) What is the net force? 50 N LEFT c) Will the box move? YES d) If yes, in what direction? LEFT 50 N NET FORCE 14) Two movers are trying to move a heavy chair. One mover PULLS to the left with a force of 200 N. The other mover PUSHES to the left with a force of 200 N. a) Draw & label the forces on the diagram. b) What is the net force? 400 N LEFT c) Will the chair move? YES d) If yes, in what direction? LEFT 400 N NET FORCE 200 N 200 N 15) Four children are fighting over the same toy. Mike is pulling North with a 50 N force, Justin is pulling East with a 40 N force, Chantal is pulling South with a 50 N force, and Tykera is pulling West a 30 N force. a) Draw & label the forces on the diagram. b) Is there a net force on the toy? YES = 10 N EAST c) In which direction will the toy move? EAST d) Who gets the toy? JUSTIN MIKE 50 N TYKERA JUSTIN 30 N 40 N 10 N Net CHANTAL FRICTION FRICTION What will happen when the ball is released? When the ball reaches the bottom of the slope, will it keep moving forever? Since The force the ball that stops, slows there ball must to be a stop a force is acting to FRICTION. slow the ball down. What is Friction? Friction is a force that two surfaces exert on each other when they rub against each other. The direction of the friction force is always OPPOSITE to the direction of the motion. Direction of Motion Friction Types of Friction Static Friction opposes the motion of an object that is at rest To make the object move, you have to exert a force larger than the force of static friction. Types of Friction Sliding friction occurs when two solids slide over each other. Sliding friction makes car brakes work and stops athletes from slipping. Types of Friction Rolling friction occurs when an object rolls across a surface. Rolling friction is easier to overcome than sliding friction for the same materials. Direction of Motion Direction of Intended Movement Static Friction Direction of Slide Sliding Friction Friction 6

7 Types of Friction Fluid friction occurs when a solid object moves through a liquid or gas. Air resistance is a type of fluid friction. Direction of Motion Friction Which type of friction is slowing down the object in each situation? You are slipping down a waterslide at Emerald Pointe. FLUID FRICTION You use a lot of force to slide a desk across the floor. SLIDING FRICTION You re riding a skateboard down the street and it slowly rolls to a stop. ROLLING FRICTION You try to push the couch, but can t seem to move it. Friction STATIC FRICTION Friction Thought Questions Why would you add oil to a rusty bike chain? Why would you add sand to an icy driveway or road? Why is it easier to move heavy furniture using a handcart rather than pushing it? Why would a shoe company be interested in studying friction? What would happen if we repeated the tugof-war and one team had only socks on? Review of Friction s Review - What is Friction? Friction is a force that two surfaces exert on each other when they rub against each other. The direction of the friction force is always OPPOSITE to the direction of the motion. It SLOWS down moving objects! Direction of Motion What factors affect Friction? In your homework, you found out 2 factors affect friction: Types of surfaces involved How hard the surfaces push together Today, we re going to investigate DIFFERENT SURFACES to see which ones create the most friction. Friction CARPET SANDPAPER DESK What factors affect Friction? In your homework, you found out 2 factors affect friction: Types of surfaces involved How hard the surfaces push together Today, we re going to investigate DIFFERENT SURFACES to see which ones create the most friction. CARPET SANDPAPER DESK Conclusions Questions 1. Which surface material created the MOST frictional force? 2. Which surface material created the LEAST frictional force? 3. Give an example of a situation where we use a certain surface material to: a) REDUCE friction b) INCREASE friction GRAVITY & AIR RESISTANCE The physics of falling 7

8 The of Gravity Gravity is the force that pulls all objects down to the earth. Rain falls from the sky down to earth If you drop a book, it falls to the ground If you trip, you ll fall down Universal Gravitation Actually in science, gravity is a force of attraction that acts between ALL objects (the earth, you, the desk, a book) The force of gravity is much STRONGER for LARGER objects (more mass). Universal Gravitation Because the Earth is by far, the largest and closest object around, it has the greatest force of attraction... So, no matter where you are on earth, all things fall to the ground due to gravity What is free fall? When gravity is the ONLY force acting on an object, it is in free fall. In that case, gravity is an UNBALANCED FORCE which causes the object to accelerate. Acceleration due to Gravity Calculate the acceleration of an object in free fall. A = Final speed initial speed time A = 50 m/s 0 m/s 5 s Acceleration = 10 m/s 2 Objects in Free Fall Do all objects fall at the same rate? If we dropped a bowling ball and a tennis ball from the same height, which would land first? Let s try it! Mass and Gravity Oct. 24, 2008 Question: How does mass affect the speed of a falling object? Hypothesis: (What do you think will happen AND WHY?) Observations & Data Collection: Repeat each trial twice and record your observations. Ping pong ball vs. Wooden ball: Wooden ball vs. Metal ball: Ping pong ball vs. Metal ball: Conclusion: (One sentence) Objects in Free Fall Do all objects fall at the same rate? ALL objects in free fall travel at the same rate, regardless of mass! In free fall, heavy objects and light objects fall at the same rate! So, which will land first? WHY does the penny land first? Remember the force that opposes motion (slows things down)? FRICTION! Falling objects experience friction with the air called AIR RESISTANCE that slows them down. 8

9 Air Resistance The larger the object (more surface area), the more air resistance. That s why parachutes work! The upward force of the air acting on the LARGE parachute slows you down as you fall. Air Resistance Net on Feather Gravity Air Resistance Net on Penny Draw a diagram showing the forces Downward force of gravity is same on both. Upward force of air resistance is greater on the feather. The net force (down) is greater on the penny. Without air resistance, all objects would fall at the same rate Galileo Drops the Ball Hammer and Feather Drop on the Moon Gravity on the moon? The force of gravity is much weaker on the moon because It is much farther away from earth. The moon is much smaller than earth. That s why astronauts weigh less on the moon! Gravity Review Gravity is the force that pulls all objects down to the earth. When gravity is the ONLY force acting, ALL objects accelerate at a rate of 10 m/s 2. Mass doesn t matter in free fall, heavy objects and light objects fall at the same rate! Air Resistance Review Some objects take longer to fall they are slowed down by FRICTION with the air called AIR RESISTANCE. The larger the surface area, the greater the force of air resistance pushing up. Without air resistance, all objects would fall at the same rate Draw a free body diagram of the sky diver and label ALL the forces. Gravity = 1000 N Air Resistance = 800 N What is the net force? Air Resistance = 800 N Newton s 1 st Law Newton s 1 st Law of Motion After the ball is kicked, what forces are acting on it while it rolls? What if we could remove those forces? What would happen then if we kicked the ball? GRAVITY Net = 200 N Gravity = 1000 N Friction 9

10 Newton s 1 st Law of Motion Newton s 1 st law of motion states: An object at rest will remain at rest, -andan object moving at a constant velocity will continue moving at a constant velocity, -UNLESSit is acted upon by an unbalanced force. Newton s 1 st Law of Motion BASICALLY Objects That s because resist any larger change objects to their have motion! more inertia This resistance (more resistance called to INERTIA. a change in their motion)! Which one would be easier to push? or Newton s 1 st Law of Motion Unfortunately, That s because your things bed at really rest Do Make the doesn t will stay make at rest your laundry! bed! itself until an And unbalanced dirty clothes won t force pick (like your themselves arms lifting up the off the sheets) floor! acts on them. Newton s 1 st Law of Motion What The car would was acted happen upon to by the an things outside inside Inside the force car a the if moving the force car vehicle, of hit the a wall? everything hitting the is moving car. at the same velocity your body, That s because things moving at a the objects the car, and the car constant The person velocity inside the will car stay wasn t at a hit constant by the itself. velocity force of unless the wall, acted so he upon kept by moving an at the same speed and in the same direction. unbalanced force. Newton s 1 st Law of Motion Explain this animation: The truck is stopped by the force of the impact with the car, but the ladder continues to move at its original speed and in its original direction because of inertia. Newton s 1 st Law of Motion So, how did the tablecloth demo work? The cloth experienced a pulling force that caused it to start moving. The dishes did not have a direct force applied to them, so they remained in their places because of inertia. Newton s 1 st Law of Motion Following the instructions on your sheet, do each of the activities at your desk. In your notebook, write the title of each activity and explain in at least two complete sentences how it works, using Newton s 1 st Law. Newton s 2 nd Law Let s review Newton s 1 st Law This law deals with situations where forces are balanced When forces are balanced, objects resist any changes in their motion that s called INERTIA. 10

11 Newton s 1 st Law of Motion If no one kicks the ball, what will happen? Objects at rest will remain at rest Newton s 1 st Law of Motion If there was NO FRICTION (no unbalanced force) to slow down the ball, what would happen? Objects in motion will remain in motion Newton s 1 st Law of Motion The ladder s inertia keeps it moving forward after the unbalanced force (car) stops the truck Newton s 2 nd Law of Motion Newton s 2 nd law of motion describes how UNBALANCED FORCES and MASS affect the ACCELERATION of an object. Let s try it! Test 1 Increasing Small - Blow through the straw lightly toward the marble. Observe the marble s motion. Large Blow the straw with more force toward the marble. Observe the marble s motion. How does increasing the force affect the marble s acceleration? Test 2 Increasing Mass Small Mass (marble) - Blow through the straw as hard as you can. Observe the marble s motion. Large Mass (golf ball) Blow the straw as hard as you can. Observe the golf ball s motion. How does increasing the mass affect the the object s acceleration? So, how do unbalanced forces affect an object s motion? How does a batter s swing affect the acceleration of a baseball? Sacrifice Bunt Homerun Hit So, how do unbalanced forces affect an object s motion? The harder you hit, the faster it goes! The greater the force, the greater the acceleration Sacrifice Bunt Homerun Hit So, how does mass affect an object s motion? Which shopping cart would move faster with a single push? Empty Cart Full Cart 11

12 So, how does mass affect an object s motion? The fuller the cart, the slower it goes! The more mass, the less acceleration Empty Cart Full Cart Newton s 2 nd Law of Motion It states: ACCELERATION depends on the object s MASS, and the net FORCE acting on the object. We can also write it mathematically: = Mass x Acceleration Newton s 2 nd Law = Mass x Acceleration If you lower the mass but keep force the same, acceleration will increase. If you want less acceleration with the same force, you must increase the mass. M F A If you raise the mass but If you want more keep force the same, acceleration with the same acceleration will decrease. force, you must decrease the mass. Newton s 2 nd Law = Mass x Acceleration If you want less acceleration with the same mass, you must decrease the force. If you want more acceleration with the same mass, you must increase the force. Newton s 2 nd Law = Mass x Acceleration If you lower the mass but want the same acceleration, you must decrease the force. If you raise the mass but want the same acceleration, you must increase the force. Newton s 2 nd Law of Motion = Mass x Acceleration Mr. Sawyer s car ran out of gas. How much force does Mr. Sawyer need to push his 750kg car at an acceleration of 1 m/s 2? 750 kg 1 m/s 2 F = m x a F = 750 kg x 1 m/s 2 F = 750 N right Try one on your own Ms. Litwak s van runs out of gas. How much force does she need to push the 2000kg van at an acceleration of 0.5 m/s 2? 0.5 m/s 2 F = m x a F = 2000 kg x 0.5 m/s 2 F = 1000 N right Newton s Speed, 2Distance nd Law & of TimeMotion We can also write the formula like this: m F a Acceleration = Mass Mass = Acceleration = Mass x Acceleration Newton s 2 nd Law of Motion Find the golf ball s acceleration. a) The putter hits the 0.05 kg golfball with a force of 1 N. b) The driver hits the 0.05 kg golfball with a force of 8 N. 12

13 Newton s 2 nd Law of Motion Which forces are acting to get this guy up in the air? Use Newton s 2 nd law of motion to explain in words the difference in the motion of the golf balls. Newton s 3 rd Law His feet push DOWN on the ground. But wait His downward push can t be causing his upward motion. Which forces are acting to get this guy up in the air? His feet push DOWN on the ground. The ground pushes UP on the man. There must be a force pushing UP! The force of the ground pushes him UP! Newton s 3 rd Law of Motion ALL forces act in PAIRS! Action : Man s feet push DOWN on the ground. Reaction : Ground pushes UP on the man. Newton s 3 rd law says that: For every action force, there is an equal and opposite reaction force. Let s Demonstrate Stand up and face a partner with your palms touching. Push on your partners hands. Don t move your feet. The first partner to step back loses How can Newton s third law explain what happens? Newton s 3 rd Law of Motion Explain this animation using Newton s third law. Newton s 3 rd Law of Motion The man s A foot PAIR exerts OF FORCES: a backward push on the EQUAL boat FORCES, (action BUT force), while the boat IN exerts OPPOSITE a forward push on the man DIRECTIONS (reaction force). Let s Demonstrate Two people (the same size) in rolling chairs face each other with their feet touching. Only 1 student pushes. What will happen? How can Newton s third law explain what happens? 13

14 Identify the force pairs in each situation A person fires a rifle. Action gun pushes the bullet out at high speed. Reaction the bullet pushes back on the gun (recoil). Identify the force pairs in each situation A space shuttle lifts off. Action engine pushes gases down & out. Reaction the gases push the rocket up. *This upward force must be stronger than gravity pulling down on the rocket! Identify the force pairs in each situation A person stands still. Action gravity pulls the person down to the floor. Reaction the floor pushes up on the person. *You don t need MOTION for force pairs. They are everywhere! Let s Demonstrate The toy clackers work 2 different ways (watch your teacher). How can Newton s third law explain what happens? If forces are equal and in opposite directions, why don t they cancel out (and balance)? s only cancel if they These forces are acting on act on the same object. different objects! (Think about a tug of war all Action forces act on Rocket the rope). engine pushing on gases. These forces are acting Reaction different objects! Gases push on the rocket. Think about it... Why does it hurt so much when you stub your toe? When your toe exerts a force on a table, the table exerts an equal force back on your toe. The harder you hit your toe against it, the more force the the table exerts back on your toe (and the more your toe hurts). What is Momentum? Momentum is a measure of how much motion object has. It is affected by mass and velocity. The heavier an object is, the more momentum it has. It s easier to stop soccer ball coming towards you at 20 m/s than a car coming at 20 m/s. It s easier to stop car travelling at 1 km/h than a car travelling 60 km/h! Conservation of Momentum When objects collide, their total momentum is conserved (stays the same), unless outside forces act. The total amount of motion coming into a collision will also come out of the collision. 1. Place 4 coins in a row, touching each other. 2. Place the 5 th coin about 2 inches away from the end of the row, keeping it in line. 3. Lightly flick your finger forward, propelling the single coin against the others. 4.What do you observe? 5.Try it again, flicking 2 coins into a row of 3 coins. What do you observe? 14

15 Momentum Momentum can be calculated using this formula: Momentum = mass x velocity A golf ball with a mass of 0.05 kg travels at 16 m/s. A baseball with a mass of 0.15 kg travels at 7 m/s. Which ball has the greater momentum? Golf ball s momentum = 0.05 kg x 16 m/s = 0.8 kg m/s Baseball s momentum = 0.15 kg x 7 m/s = 1.05 kg m/s Work, Power & Simple Machines (Making work easier phew!) What is WORK? If you put a lot of effort into doing something and are worn out at the end, you think you ve done a lot of WORK, right? Not necessarily. If you haven t exerted a force AND moved an object some distance, you haven t done any WORK at all! What is WORK? In scientific terms, you do WORK when you exert a FORCE that causes an object to move some DISTANCE in the SAME DIRECTION of the force. Examples: Pushing a lawn mower Lifting books out of your bag Pulling a suitcase on wheels What 2 things must happen for WORK to be done? MOTION The object must move. If the object doesn t move, there is no work done. FORCE & MOTION IN THE SAME DIRECTION Movement must be in the same direction as force. If the motion is in a different direction than the force, there is no work. Is WORK being done? Pushing a car that s stuck in snow. NO! (No work because the car doesn t move). Lifting a baby out of his stroller. YES! (Baby moves in same direction as you lift) Carrying your bookbag to class. NO! ( is pulling up, but motion is sideways) Pushing a lawn mower. YES! (Mower goes in same direction as you push) Calculating WORK Calculating WORK What is POWER? WORK = FORCE x DISTANCE The greater the distance, the more you work. Eg. Pushing a car 100 m vs. Pushing a car 200 m (more work!) The greater the force, the more you work. Eg. Lifting 1 book onto a table vs. Lifting 10 books onto a table (more work!) You carry a baby that weighs 30 N upstairs to his room (3 meters above you). How much work is done? WORK = FORCE X DISTANCE WORK = 30 N x 3 meters WORK = 90 N m (90 J) Work is measured in Joules (J) 1 Joule = 1 N m Power is the rate at which work is being done (or how much work is being done in a unit of time). POWER = WORK TIME More power means less time to do the same work OR more work done in the same amount of time. Power is measured in Watts (W). 15

16 POWER Calculating POWER What are MACHINES? Think about 2 cars one with a 200 horsepower engine, and one with a 500 horsepower engine. Which one has the more powerful engine? Which one will go further in 10 minutes? Which one will go 10 miles in the shortest amount of time? A motor exerts a force of 2,000 N to lift an elevator 8.0 m in 4.0 seconds. What is the power of the motor? Power = Work = x Distance Time Time Power = 2,000N x 8 m 4 s = 16,000 J 4 s Power = 4,000 J/s (4,000 Watts) Most people think of complex, automated, technical, or electronic gadgets with motors, but machines can be much simpler. A machine is any device that lets you do WORK in an easier or more effective way. How do Machines do work? Machines make work easier by changing 3 things about the FORCE you exert to do work: AMOUNT of force you exert DISTANCE over which you exert force DIRECTION in which you exert force How do Machines work? In other words, a machine changes the strength, distance, direction of your push or pull. What is the mechanical advantage of a machine? A machine s mechanical advantage is the number of times a machine increases a force exerted on it. Mechanical = Output Advantage Input What is the mechanical advantage of a machine? You exert 10 N of force on a can opener. The can opener exerts 30 N of force on the can. What is the mechanical advantage? Mechanical = Output = 30 N Advantage Input 10 N Mechanical Advantage = 3 What are SIMPLE MACHINES? There are only 6 basic kinds of simple machines that make work easier. These 6 simple machines make up all the other compound machines we use everyday. SIX SIMPLE MACHINES The six simple machines are: Inclined Plane Wedge Screw Lever Wheel & Axle Pulley 16

17 INCLINED PLANE An inclined plane is a flat, sloped surface connecting a lower level with a higher level. INCLINED PLANE It lets you use less force over a longer distance to raise a load to a higher level. Input INCLINED PLANE: Examples Ramps (Boat ramps, wheelchair ramps) Propeller Ladders/Stairs Output WEDGE A wedge has slanting slides that taper to a thin edge it splits material apart. (A moving inclined plane!) WEDGE It converts motion in one direction, into a splitting motion that acts at right angles to the blade. Input WEDGE: Examples & Uses Ax, Knife, etc. Zippers Output Output Used in all cutting machines (to split materials apart) Lifting machines may use wedges to slide under loads SCREW A screw has a thread or groove wrapped around a central cylinder. (Another inclined plane - wrapped around a cylinder!) SCREW While turning, it converts a twisting motion into a forward or backward motion. Output Input SCREW: Examples & Uses Screws can holds things together or lift materials. Screws Screw top lids for jars/bottles Light bulb Swivel stools/chairs 17

18 LEVER A lever is rigid bar that pivots/rotates on a fixed point. The fixed point is called the fulcrum. LEVER Levers may increase the size or distance of force or change direction of the force. There are 3 types of levers. LEVERS: Examples & Uses First Class Levers: Scissors, See-saws, Pliers Second Class Levers: Staplers, Nutcrackers, Wheelbarrows Third Class Levers Shovels, baseball bats, tweezers WHEEL & AXLE A wheel and axle are 2 circles or cylinders attached together around a common axis. The larger circle is the wheel, the smaller cylinder/rod is called the axle. WHEEL & AXLE The wheel is locked to the central axle when one turns, so does the other one. A short powerful force at the axle, will move the wheel s edge a long distance. A long motion at edge of wheel, moves the axle with great force. Input Output WHEEL & AXLE: Examples & Uses Screwdriver Windmill Cars/Bicycles Rolling Pin Door Knob Fan Output Input PULLEY PULLEY PULLEY: Examples & Uses A pulley is a grooved wheel with a rope, used to raise/lower/move a load. A simple fixed pulley only changes the direction of force. Pulley systems decreases the input force, allowing you to move heavier loads. Output Output Input Input Cranes Raising a flag on a pole Window Blinds Raising a sail on a boat Clothesline 18

19 COMPOUND MACHINES Most machines are combinations of 2 or more simple machines. For example, a simple can opener is a combination of 3 simple machines: Lever Wheel & axle Wedge Simple Machines (Making work easier phew!) Machines make work easier by changing 3 things about the FORCE: The amount of force The distance of the force The direction of the force Machines make work easier by changing 3 things about the FORCE: The amount of force (eg. A ramp lets you lift a heavy object with LESS force) Machines make work easier by changing 3 things about the FORCE: The distance of the force (eg. A baseball bat lets you move your arms a short distance, but move the end of the bat a large distance). Machines make work easier by changing 3 things about the FORCE: The direction of the force (eg. The pulley on a set of window blinds lets you move the blinds UP with a DOWNWARD pull. What is the mechanical advantage of a machine? A machine s mechanical advantage is the number of times a machine increases a force exerted on it. Mechanical = Output Advantage Input What is the mechanical advantage of a machine? You exert 10 N of force on a can opener. The can opener exerts 30 N of force on the can. What is the mechanical advantage? Mechanical = Output = 30 N Advantage Input 10 N Mechanical Advantage = 3 What is the efficiency of a machine? The EFFICIENCY compares: the work you put IN to the work the machine puts OUT. An IDEAL machine is 100% efficient. INPUT WORK = OUTPUT WORK In the real world, some input work is always lost due to FRICTION between the moving parts of the machine. 19

20 What is the efficiency of a machine? EFFICIENCY = Output Work x 100% Input Work You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower? What is the efficiency of a machine? You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower? EFFICIENCY = Output Work x 100% Input Work Efficiency = 25,000 J x 100% 50,000 J Efficiency = 50% Try the rest of the practice problems on your own Mechanical = Output Advantage Input EFFICIENCY = Output Work x 100% Input Work The Physics of Rollercoasters The Early Days of Rollercoasters Wooden Coasters Racer at King s Island 1972 Length: 3415 feet Speed: 61 mph The first American rollercoaster, the Mauch Chunk Switchback Railway, c Length: 40 miles Speed: over 100 mph Revolution at Magic Mountain 1977 First Loop of the Modern Era Steel Coasters Classic Rollercoasters Viper at Magic Mountain loops, 4 corkscrews Speed: 73 mph Suspension Coasters Batman The Ride Magic Mountain

21 Stand-Up Coasters Riddler s Revenge Magic Mountain 1998 Tallest, Fastest Stand-Up Coaster Superman Superman Magic Mountain mph 415 feet tall Six Flags Great Adventure New Jersey 2005 Speed: 128 mph Height: 456 feet Kingda Ka Rollercoaster s There are two main forces which need to be considered when designing rollercoasters: Gravity Friction How Rollercoasters Work Rollercoasters are driven by gravity There is no engine attached to the cars The cars are pulled to the top of a hill and released Potential and Kinetic Energy Every rollercoaster relies on conservation of energy At the top of the hill, the rollercoaster has potential energy At the bottom of the hill, the potential energy has been converted into kinetic energy Potential Energy Potential Energy = mass x gravity x height Heavier objects have more potential energy The higher an object, the greater its potential energy Kinetic Energy Kinetic Energy = 1/2 x mass x velocity 2 Heavier objects have more kinetic energy The faster an object is moving, the greater its kinetic energy Hills K.E. = 1/2 mv 2, P.E. = mgh When cars go up a hill, their height increases and their velocity decreases When cars go down a hill, their height decreases and their velocity increases A rollercoaster can never go higher than the top of the first hill 21

22 Loops Loops are treated like hills, with one difference Cars must have enough energy to reach the top of the loop Cars must have a certain speed at the top of a loop so that they don t fall 22