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1 Slide 1 / 129 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website:

2 Slide 2 / 129 Forces Core Idea PS2 : Motion and Stability: Forces and Interactions PS2.A : Forces and Motion

3 Slide 3 / 129 Motion and Stability: Forces and Interactions Click on the topic to go to that section Motion Graphs of Motion Forces Newton's Laws of Motion Newton's 3rd Law & Momentum

4 Slide 4 / 129 Motion Return to Table of Contents

5 Slide 5 / 129 What does it mean to be in motion? An object is in motion if it changes position in relation to a reference point. References points are places or objects used to determine the motion of an object. It is extremely important to choose reference points carefully.

6 Slide 6 / 129 Relative Motion Motion is relative as it is dependent upon the reference point. Are you in motion right now? Think about it... Are you in motion compared to your desk? Are you in motion compared to the sun?

7 Slide 7 / 129 Measuring Motion Speed is one of the many ways we measure motion. Speed is a measure of the distance traveled per unit of time. That means you can find the speed of any object that is in motion!

8 Slide 8 / 129 Finding Speed Speed (m/s) = Distance (m) Time (s) If speed is distance divided by time, then distance is speed times time. So what is time? and

9 Slide 9 / 129 A m/s B.02 m/s C 600 m/s D.002 m/s Answer 1 A snail travels 10 m in 6000 seconds. What is the snail's average speed?

10 Slide 9 (Answer) / 129 A m/s B.02 m/s C 600 m/s D.002 m/s Answer 1 A snail travels 10 m in 6000 seconds. What is the snail's average speed? D [This object is a pull tab]

11 Slide 10 / 129 A 500 m/s B 4500 m/s C 4500 m D 500 m Answer 2 A blimp travels at 3 m/s for 1500 s. What distance does the blimp cover in that time?

12 Slide 10 (Answer) / 129 A 500 m/s B 4500 m/s C 4500 m D 500 m Answer 2 A blimp travels at 3 m/s for 1500 s. What distance does the blimp cover in that time? C [This object is a pull tab]

13 Slide 11 / 129 Manipulate the speed of each car, solve for time, and predict which car will win!

14 Slide 12 / 129 Speed When we talk about speed, it is important to know that there is a difference between instantaneous speed and average speed. Average speed can be calculated by dividing the total distance by the total time. Instantaneous speed is the speed of an object at any moment in time.

15 Slide 13 / 129 Average Speed vs Instantaneous Speed It might take 3 hours to travel 300 km in a car, so the average speed of the car is 100 km/h. s=d/t s = 300 km / 3 hours s = 100 km/h However, at a specific instance in time, the speed of the car might have been 92 km/h (instantaneous speed) according to the speedometer.

16 Slide 14 / 129 Average vs Instantaneous Speed Have you ever run a mile? Do you think you ran at the exact same speed the entire mile?

17 Slide 15 / 129 When your teacher times your mile run at 8.2 minutes, that means your speed was 8.2 mi/min. Was this your average speed or your instantaneous speed? A Average Speed B Instantaneous Speed Answer 3

18 Slide 15 (Answer) / 129 When your teacher times your mile run at 8.2 minutes, that means your speed was 8.2 mi/min. Was this your average speed or your instantaneous speed? A Average Speed B Instantaneous Speed Answer 3 avg speed = 8.2mi/min [This object is a pull tab]

19 Slide 16 / 129 When your teacher times your mile run at 8.2 minutes, that means your speed was 8.2 min/mi. Was this your average speed or your instantaneous speed? A Average Speed B Instantaneous Speed Answer 4

20 Slide 16 (Answer) / 129 When your teacher times your mile run at 8.2 minutes, that means your speed was 8.2 min/mi. Was this your average speed or your instantaneous speed? A Average Speed B Instantaneous Speed Answer 4 avg speed = 8.2mi/min [This object is a pull tab]

21 Slide 17 / 129 Average vs Instantaneous Speed When you ride on the bus to school, does the bus driver travel at the same speed the entire trip? School buses and other vehicles have speedometers that measure the speed of the vehicle at a specific moment in time.

22 Slide 18 / 129 Does a speedometer measure the average speed or the instantaneous speed? A Average Speed B Instantaneous Speed Answer 5

23 Slide 18 (Answer) / 129 Does a speedometer measure the average speed or the instantaneous speed? A Average Speed B Instantaneous Speed Answer 5 Instantaneous Speed [This object is a pull tab]

24 Slide 19 / 129 A swordfish travels for two hours. The first hour he covers 110 kilometers, and the second hour he covers 84 kilometers. What is the average speed of the swordfish? A 110 km/h B 84 km/h C 97 km/h D 194 km/h Hint: Remember that Average speed is total distance travelled divided by total time Answer 6

25 Slide 19 (Answer) / 129 A swordfish travels for two hours. The first hour he covers 110 kilometers, and the second hour he covers 84 kilometers. What is the average speed of the swordfish? A 110 km/h B 84 km/h C 97 km/h D 194 km/h Hint: Remember that Average speed is total distance travelled divided by total time Answer 6 C [This object is a pull tab]

26 Slide 20 / 129 A dog walks outside to go the bathroom every day. She is small and not very quick. If she walks outside at a speed of 2.5 meters per second and walks 75 meters before she is ready, how long does it take her? A 30 seconds B 2 minutes C 188 seconds D 90 seconds Answer 7

27 Slide 20 (Answer) / 129 A dog walks outside to go the bathroom every day. She is small and not very quick. If she walks outside at a speed of 2.5 meters per second and walks 75 meters before she is ready, how long does it take her? A 30 seconds B 2 minutes C 188 seconds D 90 seconds Answer 7 A [This object is a pull tab]

28 Slide 21 / 129 Velocity Velocity is another way to measure motion. Simply put, velocity is the speed of an object with direction. Since velocity has both magnitude and direction, it is a vector. Runner's speed: 10 km/hr Runner's velocity: 10 km/hr to the East

29 Slide 22 / 129 Why Velocity? So, why is velocity important? Have you ever been in an airplane? Would you want to be on that plane if air traffic controllers only told pilots the speed of the planes around them, but not the direction they were going? Tornadoes travel at about 170 km/h. If meteorologists only told you the speed of the tornado and not the direction it was traveling, would it be helpful?

30 Slide 23 / 129 Carlos and Gina are riding on their horses to go into town. They travel 70 meters in 7 seconds going west. What is their velocity? A 490 m/s west B 10 m/s west C 490 m/s D 10 m/s Answer 8

31 Slide 23 (Answer) / 129 Carlos and Gina are riding on their horses to go into town. They travel 70 meters in 7 seconds going west. What is their velocity? A 490 m/s west B 10 m/s west C 490 m/s D 10 m/s Answer 8 B [This object is a pull tab]

32 Slide 24 / 129 A car travels 100 km/h west for 2 hours. The car then travels 50 km/h east for one hour. What is the car's position relative to its starting position? A 50 km west B 150 km west C 250 km west D 50 km east Answer 9

33 Slide 24 (Answer) / 129 A car travels 100 km/h west for 2 hours. The car then travels 50 km/h east for one hour. What is the car's position relative to its starting position? A 50 km west B 150 km west C 250 km west D 50 km east Answer 9 A [This object is a pull tab]

34 Slide 25 / 129 Graphing Motion Return to Table of Contents

35 Slide 26 / 129 Graphing Motion Graphs can be used to show motion and can be used to easily determine relationships! When graphing data, position should be on the y axis and time on the x axis. The graph below shows constant speed because the speed remains throughout the entire journey. The biker covers two meters every second.

36 Slide 27 / 129 Graphing Motion When interpreting a graph, it is important to look for relationships between variables. These relationships can be strong, weak, or not present at all. A strong relationship is one where a significant change in one variable correlates with significant changes in the other variable.

37 Slide 28 / 129 Graphing Motion A weak relationship is when significant changes in one variable cause minimal changes in the other variable.

38 Slide 29 / 129 Graphing Motion When there is no relationship between the variables, there will not be a pattern present.

39 Slide 30 / 129 The Importance of Slope Position versus time graphs can be used to find speed and compare speeds. When we talk about the slope of a line, we are talking about how steep a line is. Think of skiing, the bunny trail would be rather flat while the black diamond trail would be a pretty steep mountain. In a position versus time graph, the y axis is the position and the x axis is the time, we know that the relationship between position and time is speed. So when we are looking at the slope, we are looking at the speed. The steeper the slope of the line on a position versus time graph, the greater the speed!

40 Slide 31 / 129 Which walker has a greater speed? How do you know? Answer 10

41 Slide 31 (Answer) / 129 Which walker has a greater speed? Walker #2 because the How do you know? slope is steeper. This walker covered the same distance in less time than walker #1. Answer 10 [This object is a pull tab]

42 Slide 32 / 129 Graphing Motion Click on the image to the left to launch the simulation. You will need to download it to be able to use it. Click on the CHARTS tab at the top. Minimize the velocity graph and the acceleration graph by clicking on the RED dash on each graph. KEEP POSITION! CLICK PLAY Drag the man to the RIGHT at a constant speed, STOP, and finally drag the man at a constant speed Left back to the starting point (zero). Relate the shape of the graph to the man's motion

43 Slide 33 / 129 Acceleration Constant speed is when an object's speed does not change; however, most objects do not travel at a constant speed. Acceleration is another method for measuring motion. Do you walk at the exact same speed from class to class? Probably not, which means you are accelerating!

44 Slide 34 / 129 Acceleration Acceleration occurs when there is a change in velocity. Remember, velocity is speed with direction. So acceleration occurs any time there is an increase in speed, a decrease in speed, or a change in direction. speed speed change in direction

45 Slide 35 / 129 Acceleration Formula Acceleration is a measure of the change in velocity per unit of time. acceleration = (final velocity-initial velocity) time a = vf -vo t

46 Slide 36 / A school bus driver sees an old lady crossing the street at an intersection and hits the brake pedal and turns the steering wheel to avoid her. Why did the bus accelerate? B decreased speed C changed direction Answer A increased speed

47 Slide 36 (Answer) / A school bus driver sees an old lady crossing the street at an intersection and hits the brake pedal and turns the steering wheel to avoid her. Why did the bus accelerate? B decreased speed C changed direction Answer A increased speed B&C [This object is a pull tab]

48 Slide 37 / 129 A increased speed B decreased speed C changed direction Answer 12A nitro-methane powered top fuel dragster launches from rest to race against an opponent. Why did the car accelerate?

49 Slide 37 (Answer) / 129 A increased speed B decreased speed C changed direction Answer 12A nitro-methane powered top fuel dragster launches from rest to race against an opponent. Why did the car accelerate? A [This object is a pull tab]

50 Slide 38 / 129 Example: The school bus picks you up at the bus stops and takes 60 seconds to accelerate to 120 km/h. What is the acceleration of the school bus? Answer a = vf -vo t

51 Slide 38 (Answer) / 129 Example: The school bus picks you up at the bus stops and takes 60 seconds to accelerate to 120 km/h. What is the acceleration of the school bus? Answer a = vf -vo t a = (120 km/h - 0 km/h) 60 s a = 2 km/h per second [This object is a pull tab]

52 Slide 39 / 129 Answer 13 A plane's speed increases from 25m/s to 60m/s in 5 seconds. What is the acceleration of the plane?

53 Slide 39 (Answer) / 129 Answer 13 A plane's speed increases from 25m/s to 60m/s in 5 seconds. What is the acceleration of the plane? a = (60 m/s - 25 m/s) 5s a = 7 m/s/s OR 7m/s2 [This object is a pull tab]

54 Slide 40 / 129 Answer 14 After traveling for 10 seconds, a runner reaches a speed of 12m/s. What is the runner's acceleration?

55 Slide 40 (Answer) / 129 Answer 14 After traveling for 10 seconds, a runner reaches a speed of 12m/s. What is the runner's acceleration? a = (12 m/s - 0 m/s) 10 s a = 1.2m/s2 [This object is a pull tab]

56 Slide 41 / 129 Answer 15 A parachute opens and slows a skydiver from 65m/s to 45m/s in a period of 5 seconds. What is the acceleration of the skydiver?

57 Slide 41 (Answer) / 129 Answer 15 A parachute opens and slows a skydiver from 65m/s to 45m/s in a period of 5 seconds. What is the acceleration of the skydiver? a = (45m/s - 65m/s) 5s a = -4m/s2 or decelerated 4m/s2 [This object is a pull tab]

58 Slide 42 / 129 Acceleration and Graphs If the speed and direction of an object are constant, then the acceleration is zero. ZERO a Acceleration is positive when speed is increasing, and negative acceleration (deceleration) when speed is decreasing. +a -a

59 Slide 43 / A driver hits the brakes to slow down at an intersection. As the car's speed is decreasing it has A positive acceleration B negative acceleration C no acceleration D more information is needed

60 Slide 44 / Which of the following graphs depicts the acceleration of a runner speeding up to pass someone. Time (s) x Time (s) Y x Time (s) x D Speed (m/s) Y Speed (m/s) C Y Speed (m/s) B Speed (m/s) A Y Time (s) x

61 Slide 45 / 129 Acceleration and Graphs The slope of a position versus time graph can also show acceleration. If the slope curves and gets steeper, then positive acceleration is occurring. If the slope curves and becomes less steep, then negative acceleration is occurring.

62 Slide 46 / 129 Distance vs. Time Graphs of Accelerating Objects Click on the image to download the simulation. Click on the CHARTS tab. Type in 1 m/s2 into the acceleration value and hit play. Sketch the shape of the distance vs. time graph: Sketch the shape of the velocity vs. time graph:

63 Slide 47 / 129 of the following speed vs time graphs depicts the position vs time graph shown in the graph below? Answer 18Which A [This object is a pull tab] A B C

64 Slide 47 (Answer) / 129 of the following speed vs time graphs depicts the position vs time graph shown in the graph below? Answer 18Which A [This object is a pull tab] A B C

65 Slide 48 / 129 Forces Return to Table of Contents

66 Slide 49 / 129 What Are Forces? Forces are pushes or pulls in a given direction. Forces affect how objects move.

67 Slide 50 / 129 Forces Affect Motion Forces can affect motion by making objects: start moving move faster move slower stop moving change direction change shape

68 Slide 51 / 129 The Big Idea... Since forces can cause changes in the speed or direction of an object, we can say that forces cause changes in velocity, so forces cause acceleration! Forces cause Acceleration

69 Slide 52 / 129 Units of Force Forces are measured in newtons (N). You probably measure yourself on a scale in pounds. One pound is equal to newtons. Just like velocity, force is a vector so when forces are demonstrated both magnitude and direction should be shown. 10 N

70 Slide 53 / 129 Balanced Forces Two or more opposite forces are balanced forces if their effects cancel each other out and they do not cause a change in an object's motion. If two or more forces of equal strength act on an object in opposite directions, the forces will cancel, resulting in a net force of zero and no change in motion. 8N 8N The box is at rest, so it will remain at rest since the forces acting on it are balanced.

71 Slide 54 / 129 Unbalanced Forces If the effects of the forces don't cancel each other out (one force is stronger than others), the forces are unbalanced forces. Unbalanced forces cause a change in motion; speed and/or direction. 15 N 8N One way to interpret this diagram is to say there is a 15N force to the right and an 8N force to the left OR we can say there is a +15N force and a -8N force. The negative tells us that the object is moving to the left.

72 Slide 55 / 129 Unbalanced Forces 15 N 8N The box was at rest. Since the forces acting on the box are unbalanced, the box will start moving to the right.

73 Slide 56 / 129 are all around us. Which of the following do you think are examples of forces? (choose all that apply) A Gravity B Friction C Muscles D Wind Answer 19Forces

74 Slide 56 (Answer) / 129 are all around us. Which of the following do you think are examples of forces? (choose all that apply) A Gravity B Friction C Muscles D Wind Answer 19Forces A&B [This object is a pull tab]

75 Slide 57 / What is the SI unit for force? B Kilograms C Newtons Answer A Pounds

76 Slide 57 (Answer) / What is the SI unit for force? B Kilograms C Newtons Answer A Pounds C [This object is a pull tab]

77 Slide 58 / Because forces have both size and direction we consider them as a: B vector C scalar D calculated quantity Answer A directional quantity

78 Slide 58 (Answer) / Because forces have both size and direction we consider them as a: B vector C scalar D calculated quantity Answer A directional quantity B [This object is a pull tab]

79 Slide 59 / A +10 N force acts on a car and at the same time, a -20 N force acts on the car. What is the net force acting on the car and is it balanced? B -10 N unbalanced C -10 N balanced D + 30 balanced Answer A -30 N unbalanced

80 Slide 59 (Answer) / A +10 N force acts on a car and at the same time, a -20 N force acts on the car. What is the net force acting on the car and is it balanced? B -10 N unbalanced C -10 N balanced D + 30 balanced Answer A -30 N unbalanced B [This object is a pull tab]

81 Slide 60 / 129 Friction Forces are present all around us, but can usually not be seen. Friction is a force that resists motion and we experience daily. When you run, walk, sit on the couch, brush your hair, and write you experience friction. You are experiencing friction right now!

82 Slide 61 / 129 Friction The force of friction is caused by microscopic particles touching each other. These microscopic pieces on both surfaces cause friction. Friction is affected by how hard the surfaces push together and the types of surfaces involved. There are many types of friction including static, sliding, rolling, and fluid friction. Click here to see the force of friction clip

83 Slide 62 / 129 Static Friction Static friction acts on objects that are not moving. Have you ever wondered why it is so hard to start moving a heavy object like a dresser or couch, but then once it starts moving it is easier? That is because you have to overcome the force of static friction!

84 Slide 63 / 129 Sliding Friction Sliding friction occurs when objects slide over each other. Sliding friction is easier to overcome than static friction. That is why the couch is easier to move once it starts sliding! Click here to see sliding friction in action.

85 Slide 64 / 129 Fluid Friction Fluid friction occurs when objects move through a fluid. Remember, air is a fluid, so you continuously experience fluid friction! Click here to see the effects of fluid friction.

86 Slide 65 / 129 Rolling Friction Rolling friction exists when objects roll across surfaces. When you go bowling, roller skating, bicycling, or play soccer, rolling friction is present.

87 Slide 66 / 129 Friction The force of friction is represented by a force vector and measured in Newtons like all other forces. When you are trying to determine where to put the friction force, just remember that friction acts opposite to motion! force applied by person pushing box stationary box static friction force

88 Slide 67 / Friction acts more in motion than it does at rest. False Answer True

89 Slide 67 (Answer) / Friction acts more in motion than it does at rest. False Answer True False [This object is a pull tab]

90 Slide 68 / 129 Gravity Forces are present all around us and always act in pairs, so we usually experience more than one force. Gravity is another force that pulls objects towards each other. The Law of Universal Gravitation tells us that gravity acts between all objects in the universe. This means that without exception, any two objects in the universe attract each other!

91 Slide 69 / 129 Factors affecting Gravity Gravity is affected by both mass and distance. The greater the distance between two objects, the less the gravitational force between them. The greater the mass of the object, the greater the object's gravitational force. (mass: a measure of the amount of matter in an object. We will use kg as our unit of measure for mass.) Greater gravitational force exists between the objects of greater mass below...

92 Slide 70 / The force of gravitation between an object and a planet is increased as they move away from each other: False Answer True

93 Slide 70 (Answer) / The force of gravitation between an object and a planet is increased as they move away from each other: False Answer True False [This object is a pull tab]

94 Slide 71 / 129 Wait, so mass affects gravity? Then, what is weight? Weight is a measure of the gravitational force exerted on an object. Weight varies depending on gravitational force, but mass does not. Weight = mass x gravity Did you know that you would weigh # one sixth of your weight on the moon?

95 Slide 72 / 129 What is "g"? g = acceleration due to gravity. Near Earth's Surface, g = 9.8 m/s 2 Jupiter g = 26.1 m/s2 Earth's Moon g = 1.67 m/s2 On other planets, acceleration due to gravity will vary depending on the mass of the planet. In general, the bigger the planet, the bigger the value of g!

96 Slide 73 / A 50 kg kid is on planet Earth, where g = 9.8 m/s 2. What is the boy's weight? B 490 N C 490 kg D 5.1 N Answer A 5.1 m/s

97 Slide 73 (Answer) / A 50 kg kid is on planet Earth, where g = 9.8 m/s 2. What is the boy's weight? B 490 N C 490 kg D 5.1 N Answer A 5.1 m/s B [This object is a pull tab]

98 Slide 74 / 129 A 83.5 kg B 29.9 kg C 83.5 N D 29.9 N Answer 26A 50 kg kid is on the moon, where g = 1.67 m/s 2. What is the boy's weight?

99 Slide 74 (Answer) / 129 A 83.5 kg B 29.9 kg C 83.5 N D 29.9 N Answer 26A 50 kg kid is on the moon, where g = 1.67 m/s 2. What is the boy's weight? C [This object is a pull tab]

100 Slide 75 / 129 Gravity and Motion When an object is in free fall, it accelerates at 9.8 m/s 2 So, would a penny and an elephant that are dropped off the top of the Empire State Building accelerate at the same rate if they were in free fall? Yes!! free fall: gravity is the only force acting on the object air resistance: fluid friction experienced by objects falling through the air As objects fall through the air, they experience air resistance. This upward force exerted on falling objects increases with surface area and velocity.

101 Slide 76 / 129 Equilibrium As you know, many forces are acting on us and other objects. To determine the total force acting on an object, the forces are added and subtracted as appropriate to find the net force. When several forces are acting on the same object, the net force might be zero... 5N -5 N Net Force = 0 If the net force on an object is zero, then it is in equilibrium. When an object is at rest, the net force is zero.

102 Slide 77 / 129 Unbalanced Forces If the net force is not equal to zero, then there is a change in the motion of the object. 5N -12 N Net Force = -7 Unbalanced forces cause an object to Accelerate!

103 Slide 78 / 129 Unbalanced Forces 5N -12 N Net Force = -7 a In this case, the object will accelerate towards the left because the NET FORCE is toward the left.

104 Slide 79 / 129 Unbalanced Forces 5N -12 N Net Force = -7 a In this case, the object will accelerate towards the left because the NET FORCE is toward the left. On Earth, gravity and friction are two of the unbalanced forces that frequently change an object's motion.

105 Slide 80 / What is the net force acting on the object below? Is the object in equilibrium? Answer -10 N 7N -8 N

106 Slide 80 (Answer) / What is the net force acting on the object below? Is the object in equilibrium? 7N Answer -10 N -11 N [This object is a pull tab] -8 N

107 Slide 81 / What is the net force acting on the object below? Is the object in equilibrium? Answer -10 N 25 N -15N

108 Slide 81 (Answer) / What is the net force acting on the object below? Is the object in equilibrium? 25 N Answer -10 N 0N [This object is a pull tab] -15N

109 Slide 82 / 129 due to gravity on Jupiter is 26.1 m/s2. How much would a 60 kg person weigh on Jupiter? Answer 29Acceleration

110 Slide 82 (Answer) / 129 due to gravity on Jupiter is 26.1 m/s2. How much would a 60 kg person weigh on Jupiter? Answer 29Acceleration 1566 N [This object is a pull tab]

111 Slide 83 / 129 due to gravity on Earth's Moon is 1.67 m/s2. How much would a 60 kg person weigh on Earth's Moon? Answer 30Acceleration

112 Slide 83 (Answer) / 129 due to gravity on Earth's Moon is 1.67 m/s2. How much would a 60 kg person weigh on Earth's Moon? Answer 30Acceleration N [This object is a pull tab]

113 Slide 84 / 129 Newton's Laws of Motion Return to Table of Contents

114 Slide 85 / 129 The History of the Laws of Motion Aristotle, a Greek philosopher, and Galileo Galilei, an Italian astronomer, may have been two of the first scientists to try to explain gravity and motion.

115 Slide 86 / 129 The History of the Laws of Motion In the late 1600s, Sir Isaac Newton used Galileo's ideas to create three basic laws of motion. Sir Isaac Newton contributed to advances in physics, mathematics, and astronomy.

116 Slide 87 / 129 Laws of Motion Newton may be one of the greatest scientists in history. The three laws of motion he created are three of the most used natural laws in science. These laws help us to make sense of the world around us!

117 Slide 88 / 129 Laws of Motion Newton was inspired by the apple falling from the tree and asked himself if gravity might also be the force holding the moon in orbit. Newton found that gravity plays a role in other orbital motions as well!

118 Slide 89 / 129 Newton's First Law of Motion The first law of motion tells us that an object at rest stays at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless acted on by an unbalanced force. On Earth, gravity and friction are two of the unbalanced forces that frequently change an object's motion.

119 Slide 90 / 129 Newton's First Law of Motion The first law of motion is sometimes referred to as the law of inertia. Inertia: the tendency of an object to resist a change in motion

120 Slide 91 / 129 The First Law of Motion The first law basically tells us that motion will not change without a net force. So, if an object stops moving or starts moving, you know there is a net force. If there is a net force, then the forces are unbalanced. As you know, unbalanced forces cause changes in motion! Click on image to the left to launch simulation Click on the motion tab, check speed to add speedometer, and place a person on the skateboard. Apply a force to the object and look at the speedometer. What happened? Stop applying the force. What happens?

121 Slide 92 / 129 Application of The First Law of Motion Have you ever wished that you could just tell your clothing to move itself to the closet? Unfortunately, we know that objects don't move on their own. An unbalanced force is required to make an object change its state of motion.

122 Slide 93 / 129 Application of The First Law of Motion Imagine you need to move a few pieces of furniture in your room. Would you rather move your dresser with everything in it or your dresser with nothing in it? The dresser that is filled has a greater mass, so it would have greater inertia meaning that it is more resistant to change.

123 Slide 94 / Inertia is the reluctance any material object has to change in its state of motion. False Answer True

124 Slide 94 (Answer) / Inertia is the reluctance any material object has to change in its state of motion. False Answer True True [This object is a pull tab]

125 Slide 95 / The law of inetria applies to: B nonmoving objects C both moving and nonmoving objects Answer A moving objects

126 Slide 95 (Answer) / The law of inetria applies to: A moving objects nonmoving objects C both moving and nonmoving objects Answer B C [This object is a pull tab]

127 Slide 96 / 129 Which has more Inertia? A Tennis Ball or a Bowling Ball? Why?

128 Slide 97 / Which object has the greatest inertia? Tennis B Ball C Freight Train Answer A Car

129 Slide 97 (Answer) / Which object has the greatest inertia? Tennis B Ball C Answer A Car C Freight Train [This object is a pull tab]

130 Slide 98 / A ball will accelerate and increase it's velocity when it feels a balanced force. False Answer True

131 Slide 98 (Answer) / A ball will accelerate and increase it's velocity when it feels a balanced force. False Answer True FALSE [This object is a pull tab]

132 Slide 99 / 129 Newton's Second Law Newton's second law states that acceleration is dependent on both force and mass. Unbalanced forces cause acceleration. Remember, acceleration is an increase in speed, a decrease in speed, or a change in direction. According to the second law... Unbalanced forces cause acceleration. Forces that cause a net force on an object are unbalanced. There is a direct relationship between force and acceleration. As force increases, acceleration increases. Mass and acceleration are inversely proportional. As mass increases, acceleration decreases.

133 Slide 100 / 129 Newton's Second Law Unbalanced forces cause acceleration, so unbalanced forces cause an increase in speed, a decrease in speed, and/or a change in direction. The second law relates force, mass, and acceleration. Acceleration (m/s2) = Force (N) / Mass (kg) Therefore, Force = mass x acceleration F = ma

134 Slide 101 / 129 Newton's Second Law The formula for Newton's Second Law is: F = ma We can rearrange this to solve for the other variables. You do not need to know how to rearrange it, but you do have to be able to select the right formula for solving your problem. a= F m m= a F

135 Slide 102 / 129 Application of Newton's Second Law The second law states that if force is increased, acceleration will increase. Have you ever played with toy cars? Did you notice that the harder you push the car, the faster the car speeds up?

136 Slide 103 / 129 Newton's 2nd Law Simulation Click on the image to the left to download the Simulation. Click the Acceleration Lab Tab Check show Forces, masses, acceleration, and turn gravity to none. Place 1 crate onto the surface and apply a 500 N force, note the acceleration. Stack 2 crates onto the surface and apply a 500 N force,note the acceleration. What was the effect of adding mass to the simulation on the resulting acceleration produced?

137 Slide 104 / 129 Application of Newton's Second Law The second law also tells us that the greater the mass, the less the acceleration (if the force is constant). Have you ever pulled your brothers and sisters in a red wagon? The more mass in the wagon, the slower the wagon speeds up!

138 Slide 105 / When the force acting on an object increases, the resulting acceleration will: B increase C decrease Answer A remain constant

139 Slide 105 (Answer) / When the force acting on an object increases, the resulting acceleration will: B increase C decrease Answer A remain constant B [This object is a pull tab]

140 Slide 106 / When the objects mass is increased but the applied force stays the same, the resulting acceleration will: B increase C decrease Answer A remain constant

141 Slide 106 (Answer) / When the objects mass is increased but the applied force stays the same, the resulting acceleration will: B increase C decrease Answer A remain constant C [This object is a pull tab]

142 Slide 107 / You are riding your bicycle to the park to meet a few friends. As you ride, you apply a force of 30 N and accelerate at a rate of 0.4 m/s2. What is the total mass of the bicycle and you? B 12 kg C 120 kg Answer A 75 kg

143 Slide 107 (Answer) / You are riding your bicycle to the park to meet a few friends. As you ride, you apply a force of 30 N and accelerate at a rate of 0.4 m/s2. What is the total mass of the bicycle and you? B 12 kg C 120 kg Answer A 75 kg A [This object is a pull tab]

144 Slide 108 / 129 Newton's 3rd Law of Motion Return to Table of Contents

145 Slide 109 / 129 Newton's Third Law of Motion Newton's third law of motion differs from the first and second because it pertains to forces between interacting objects. When you kick a soccer ball, do you feel the force of the ball against your foot? Newton's third law explains this occurrence.

146 Slide 110 / 129 Newton's Third Law of Motion Have you ever jumped off the side of a boat and noticed that the boat travels away from you? This is Newton's third law of motion at work! You applied a force to the boat and the boat applied an equal and opposite force on you.

147 Slide 111 / When you sit on a chair, the chair pushes back with more force than your weight. False Answer True

148 Slide 111 (Answer) / When you sit on a chair, the chair pushes back with more force than your weight. False Answer True False [This object is a pull tab]

149 Slide 112 / Action-Reaction forces are always found in pairs that are equal and opposite. False Answer True

150 Slide 112 (Answer) / Action-Reaction forces are always found in pairs that are equal and opposite. False Answer True True [This object is a pull tab]

151 Slide 113 / 129 Newton's Third Law of Motion As you may remember from before, forces always exist in pairs! Newton's third law defines these action and reaction forces. Click here to see how Newton's Third Law applies to the physics of a rocket.

152 Slide 114 / 129 Newton's Third Law of Motion As you kick the soccer ball, you apply an action force to the ball, and the ball applies a reaction force on your foot. These forces are equal in strength and opposite in direction. Since you have a greater mass than the ball, the ball accelerates more quickly. Just like when you jump off a boat, you accelerate more quickly than the boat because you have less mass!

153 Slide 115 / 129 Newton's Third Law of Motion n t io ac re ac t io n The third law states that for every action force, there is an equal, but opposite reaction force. This means that if one object applies a force to another object, then the other object exerts an equal and opposite force on the first object.

154 Slide 116 / 129 So, why don't these forces cancel each other out? They are not acting on the same object!! Each force is acting on a different object. The bat applies force to the ball that changes the direction of the ball, and the ball applies an equal and opposite force on the bat.

155 Slide 117 / 129 The Truth about Action Reaction Forces If a force occurs, there are action reaction forces! Action Reaction forces can cause changes in motion. Action Reaction forces are equal in strength, yet opposite in direction. The Action force never acts on the same object as the Reaction force.

156 Slide 118 / 129 Which of the following statements pertains to the third law of motion? Action and Reaction pairs always A act on the same object. B Mass is indirectly proportional to acceleration. C An object at rest will remain at rest unless acted on by an unbalanced force. D If a force occurs, action reaction forces are present. Answer 40

157 Slide 118 (Answer) / 129 Which of the following statements pertains to the third law of motion? Action and Reaction pairs always A act on the same object. B Mass is indirectly proportional to D acceleration. C An object at rest will remain at rest unless acted on by an unbalanced force. D If a force occurs, action reaction forces are present. Answer 40 [This object is a pull tab]

158 Slide 119 / 129 Momentum Newton's third law tells us that action reaction forces are equal and opposite, but that does not mean that the effects of those forces are equal. The forces might cause different changes in motion on the objects!

159 Slide 120 / 129 Momentum Think about two sumo wrestlers running into each other. If one has a greater mass, when they collide, one will experience a greater change in motion even though the force on each other is the same.

160 Slide 121 / 129 Momentum If we understand Newton's third law and momentum, we can predict how the motion of colliding objects will change. Momentum is the result of the mass of the object times the object's velocity. momentum (kg-m/s) = mass (kg) x velocity (m/s)

161 Slide 122 / 129 Momentum Find the momentum of a skateboarder with a mass of 50 kg traveling at a velocity of 4 m/s west. p = mv p = (50 kg)(4 m/s) p = 200 kg m/s

162 Slide 123 / How can a small insect have the same momentum as a large car? B both car and insect are at rest C insect has no mass D A&B Answer A insect has large speed

163 Slide 123 (Answer) / How can a small insect have the same momentum as a large car? A insect has large speed both car and insect are at rest C insect has no mass D A&B Answer B D [This object is a pull tab]

164 Slide 124 / If a 2 kg toy truck is moving at 4 m/s, what is the toy's momentum? B 2 kgm/s C 8 kgm/s D 8 m/s Answer A 3 m/s

165 Slide 124 (Answer) / If a 2 kg toy truck is moving at 4 m/s, what is the toy's momentum? B 2 kgm/s C 8 kgm/s D 8 m/s Answer A 3 m/s C [This object is a pull tab]

166 Slide 125 / 129 Law of Conservation of Momentum Momentum is conserved (remains the same) during an interaction as long as the objects are not affected by outside forces. This means that the total momentum of objects prior to an interaction will equal the total momentum of the objects after the interaction. Any momentum lost by one object is gained by the other!

167 Slide 126 / 129 Momentum Simulation Click on the image to the left to launch and download the simulation. Make each object the same mass by moving sliders (1 kg each works best). Click show values. Compare the total momentum of the balls added before and after the collision. What happens to the total amount of momentum before and after the collision?

168 Slide 127 / What two factors does momentum depend on? A mass and volume C mass and velocity D mass and force Answer B mass and acceleration

169 Slide 127 (Answer) / What two factors does momentum depend on? A mass and volume C mass and velocity D mass and force Answer B mass and acceleration C [This object is a pull tab]

170 Slide 128 / The total amount of momentum before and after a collision may vary. True Answer False

171 Slide 128 (Answer) / The total amount of momentum before and after a collision may vary. True Answer False FALSE [This object is a pull tab]

172 Slide 129 / 129