1. NEWTON’S LAWS OF MOTION

2. 1st Law Inertia
An object at rest will stay at rest.

3. 1st Law Inertia
An object in motion will stay in motion

4. 1st Law Inertia An object will stay in its current condition
until acted upon by another force.

5. Balanced Force
Equal forces in opposite
directions produce no motion

6. Unbalanced Forces Unequal opposing forces produce an unbalanced force
causing motion

7. If objects in motion tend to stay in motion, why don’t moving objects keep moving forever?
Things don’t keep moving forever because there’s almost always an unbalanced force acting upon them.
A book sliding across a table slows down and stops because of the force of friction.
If you throw a ball upwards it will eventually slow down and fall because of the force of gravity.

8. Newton’s First Law – Law of Inertia
Mass is the measure of the amount of matter in an object.
Inertia is a property of an object that describes how much it will resist change to the motion of the object
More mass = more Inertia

9. Newton’s First Law – Law of Inertia
Unless acted upon by an unbalanced force, this soccer ball would sit on the ground forever.

10. What is this unbalanced force that acts on an object in motion?
Friction!
There are four main types of friction:
Sliding friction: ice skating
Rolling friction: bowling
Fluid friction (air or liquid): air or water resistance
Static friction: initial friction when moving an object

11. Newton’s First Law – Law of Inertia
Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction) the soccer ball would never stop!

12. Inertia

13. How To Apply Newton’s 1st Law of Motion

14. How To Apply Newton’s 1st Law of Motion
Estimated 19 Miles/Gallon HWY
Estimated 9 Miles/Gallon City
WHY?????

15. Newton’s 2nd Law of Motion
Once an object is moving, it will move in a straight line until acted upon by another force.
Force = ma (F=ma)

16. Force = Mass x Acceleration (F=ma)
Newton’s Second Law
Force = Mass x Acceleration (F=ma)
ACCELERATION of GRAVITY (Earth) = 9.8 m/s2
Weight (force) = mass x gravity (Earth)
Moon’s gravity is 1/6 of the Earth’s
If you weigh 420 Newtons on earth, what will you weigh on the Moon?
70 Newtons

17. Newton’s Second Law
One rock weighs 5 Newtons. The other rock weighs 0.5 Newtons. How much more force will be required to accelerate the first rock at the same rate as the second rock?
Ten times as much

18. How To Apply Newton’s 2nd Law of Motion

19. How To Apply Newton’s 2nd Law of Motion

20. How to apply F=ma
Before…

21. How to apply F=ma
After!

22. Newton’s 3rd Law of Motion
For every action there is an EQUAL and OPPOSITE reaction.

23. Newton’s 3rd Law of Motion
Table to
book
Book to
earth

24. Action and Reaction on Different Masses
Action: earth pulls on you
Reaction: you pull on earth

25. Action: rocket pushes on gases
Reaction: gases push on rocket
Action: rocket pushes on gases

26. Think about it . . .
What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force.
Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).

27. Newton’s 3rd Law of Motion
A bug with a mass of 5 grams flies into the windshield of a moving 1000kg bus.
Which will have the most force?
The bug on the bus
The bus on the bug

28. Newton’s 3rd Law of Motion
Without the acceleration, it is impossible to know!
Force (bug)= m x a
Force (bus)= m x a

29. How To Apply Newton’s
3rd Law of Motion

30. How To Apply Newton’s
3rd Law of Motion

31. Consider hitting a baseball with a bat
Consider hitting a baseball with a bat. If we call the force applied to the ball by the bat the action force, identify the reaction force.
(a) the force applied to the bat by the hands
(b) the force applied to the bat by the ball
(c) the force the ball carries with it in flight
(d) the centrifugal force in the swing
(b)

32. Newton’s 3rd Law of Motion
A rich merchant finds himself stranded in the middle of a frozen lake. Don't ask how he got there. Think Twilight Zone... The surface is perfectly frictionless. All he has is his clothing and a large bag of gold coins. How can he save himself?

33. What Laws are represented?

34. Review Newton’s First Law:
Objects in motion tend to stay in motion and objects at rest tend to stay at rest unless acted upon by an unbalanced force.
Newton’s Second Law:
Force equals mass times acceleration (F = ma).
Newton’s Third Law:
For every action there is an equal and opposite reaction.

35. Newton's Laws
1stlaw: Homer is large and has much mass, therefore he has much inertia. Friction and gravity oppose his motion.
2nd law: Homer’s mass x 9.8 m/s/s equals his weight, which is a force.
3rd law: Homer pushes against the ground and it pushes back.

36. A person is traveling at 20 m/s in a car when the car hits a tree
A person is traveling at 20 m/s in a car when the car hits a tree. The person comes to a complete stop in 0.4 seconds. What was the person’s acceleration?

37. A person is traveling at 20 m/s in a car when the car hits a tree
A person is traveling at 20 m/s in a car when the car hits a tree. The person comes to a complete stop in 0.4 seconds. What was the person’s acceleration?
a = (0 m/s – 20 m/s)/0.4 s = –50 m/s2

38. You throw a ball to a friend. If the ball has a mass of0
You throw a ball to a friend. If the ball has a mass of0.15kg and it accelerates at 20m/s, what force did you exert on the ball.

39. You throw a ball to a friend. If the ball has a mass of0
You throw a ball to a friend. If the ball has a mass of0.15kg and it accelerates at 20m/s, what force did you exert on the ball.
F = m x a
F = 0.15 x 20 = 3N

40. You throw a 0. 5 kg ball with a force of 10N
You throw a 0.5 kg ball with a force of 10N. What is the ball’s acceleration?

41. M = 0.5 F = 10 N Acceleration = a A = F/m 10 N / 0.5 kg = 20m/s2
You throw a 0.5 kg ball with a force of 10N. What is the ball’s acceleration?
M = 0.5
F = 10 N
Acceleration = a
A = F/m
10 N / 0.5 kg = 20m/s2

42. Force & Motion
Thinking Questions

43. Can an object’s acceleration be a negative number? Why or why not?

44. Can an object’s acceleration be a negative number? Why or why not?
Yes. When an object slows down and the final speed is less than the initial speed, the object’s acceleration will be a negative number.

45. If forces occur in equal but opposite pairs, how can anything ever move?

46. Read more about this here:
If forces occur in equal but opposite pairs, how can anything ever move?
According to Newton’s third law, the equal and opposite forces work on different objects.
Read more about this here:

47. Two crates, one heavy and one light, are at rest on a waxed floor
Two crates, one heavy and one light, are at rest on a waxed floor. Which crate will need a greater force to provide the same acceleration? Use the concept of inertia to explain your answer.

48. Two crates, one heavy and one light, are at rest on a waxed floor
Two crates, one heavy and one light, are at rest on a waxed floor. Which crate will need a greater force to provide the same acceleration? Use the concept of inertia to explain your answer.
The heavy crate has more inertia, so it requires more force to make it accelerate.

49. Explain the role of friction in walking on a sidewalk versus walking on a sidewalk covered with ice.

50. Explain the role of friction in walking on a sidewalk versus walking on a sidewalk covered with ice.
Friction between your shoe and the sidewalk allows you to push against the sidewalk. Ice decreases this friction.

51. You sit on a rock. Your weight is a force acting on the rock
You sit on a rock. Your weight is a force acting on the rock. What force acts on you?

52. You sit on a rock. Your weight is a force acting on the rock
You sit on a rock. Your weight is a force acting on the rock. What force acts on you?
The rock provides an upward force that is equal to your weight since you are not moving.

53. How is acceleration related to change in speed?

54. How is acceleration related to change in speed?
Acceleration is the change in velocity divided by the time needed for the change to occur, and velocity changes when speed changes.

55. Forces & Motion Review

56. Describe Acceleration

57. Describe Acceleration
A change in velocity – which may be:
A change in speed
Starting
Stopping
Speeding up
Slowing down
A change in direction
Acceleration is caused by unbalanced forces
More

58. Describe Acceleration
Deceleration is also called negative acceleration - it means an object is slowing down
When acceleration is calculated, it may be a negative number

59. Describe Speed

60. Describe Speed A way to describe motion
Average speed - Rate of motion calculated by dividing the distance traveled by the amount of time it takes to travel that distance
Constant speed - Speed that does not change
Instantaneous speed - Speed of an object at any given time

61. What is the formula used to calculate speed?

62. What is the formula for calculating speed?
Speed is calculated by dividing distance by time –

63. Calculate This Speed
A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running?

64. Remember to include the UNITS!!
Calculate this Speed:
A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running?
Speed = Distance ÷ Time
Speed = 100 m ÷ 20 s
Speed = 5m/s
Remember to include the UNITS!!

65. Explain Balanced Forces

66. Explain Balanced Forces
When all the forces acting on an object balance each other
Balanced forces do not cause a change in motion

67. Describe Friction

68. Describe Friction
Force that resists motion between two touching surfaces
Acts in the opposite direction of the object’s motion
Produces heat

69. Explain Inertia

70. Explain Inertia
Moving objects tend to continue moving unless acted upon by an unbalanced force
Objects at rest tend to stay at rest unless acted upon by an unbalanced force
The more mass an object has, the more inertia it has
More massive objects are harder to start moving and stop moving
Smaller objects are easier to start and stop moving
More

71. Explain Inertia
Newton’s First Law on Motion describes the idea of inertia
An object at rest or in constant motion is acted upon by balanced forces – an unbalanced force will change the motion
Acceleration of an object at rest or in constant motion is 0 m/s/s (no motion)

72. Explain Newton’s First Law of Motion

73. Explain Newton’s First Law of Motion
Describes the idea of inertia
Click the link below to observe the law
When you are finished, click the back button on your browser to return to this tutorial

74. Explain Newton’s Second Law of Motion

75. Explain Newton’s Second Law of Motion
Describes motion created by unbalanced forces
Mass and acceleration change in opposite ways
The more mass an object has, the more force it take to accelerate the object, the slower it accelerates
The less mass an object has, the less force it take to accelerate the object, the faster it accelerates
More

76. Explain Newton’s Second Law of Motion
Click on the link below to observe the law:
When you are finished, click the back button on your browser to return to this tutorial

77. Explain Newton’s Third Law of Motion

78. Explain Newton’s Third Law of Motion
Describes why forces act in pairs
For every action there is an equal and opposite reaction
Action and reaction forces are equal forces acting in opposite directions on different objects

79. Explain Newton’s Third Law of Motion
Click the link below to observe the law

80. Distinguish Between Speed & Velocity

81. Distinguish Between Speed and Velocity
Speed describes distance and time
Velocity describes distance, time, and direction

82. How Can Forces Affect Objects?

83. How Can Forces Affect Objects?
Slow them down
Speed them up
Stop them
Start them
Change their direction
Change their shape

84. Click here for more review: