1. Chapter 12
Forces and Motion

2. Force
Force is a push or a pull.

6. A resting object to move
Force
A force can cause:
A resting object to move
Accelerate a moving object By changing the object's
Speed
Direction

7. Measuring Force

8. lbs - Pound
N - Newton
Measuring Force

9. Connecting Motion and Forces
Force (newton, N): A push or pull one body exerts on another.
Earth

10. Balanced Forces
Balanced Forces: Forces on an object that are equal in size and opposite in direction.

11. Unbalanced Forces
Unbalanced Forces: Forces on an object are not equal resulting in a Net Force.
5 N
3 N

12. Unbalanced Forces
Unbalanced Forces: When an unbalanced force acts on an object, the object accelerates.
5 N
3 N

13. A Net Force on an object always changes the velocity of the object.

14. Balanced Forces
Balanced Forces: When the forces on an object are balanced, the net force is zero and there is no change in the object's motion.

15. Friction
Force that opposes the motion of objects that touch as they move past each other.

17. Static Friction
A friction force that acts on objects that are not moving.

18. Sliding Friction
A friction force that opposes the motion of an object as it slides over a surface.

19. Rolling Friction

20. Rolling Friction
A friction force that acts on rolling objects, caused by the change in shape at the point of rolling contact.

21. Fluid Friction
Air Resistance

22. Fluid Friction

23. A friction force that opposes the motion of an object through a fluid.
Fluid Friction
A friction force that opposes the motion of an object through a fluid.

24. Gravity
Gravity: Every object in the universe exerts a force on every other object. This force is Gravity!!!

25. Gravity
Gravity causes objects to accelerate downward, whereas air acts in the direction opposite to the motion and reduces acceleration.

26. Gravity
Air Resistance

27. Projectile Motion

28. Projectile Motion

29. Projectile Motion
Horizontal
Component
Vertical
Component

30. Projectile Motion
The combination of initial forward velocity and the downward vertical force of gravity causes the ball to follow a curved path.

31. Physical Science: 12-1
Worksheet: 12-1
Due:3/4/04

32. Force was required to keep an object moving at a constant speed.
Aristotle

33. Object will move indefinitely
Aristotle
Object will move indefinitely
if no force is applied.

34. Newton

35. Newton

36. Newton

37. Inertia
Inertia (mass): The tendency of an object to resist any change in its motion.
25 kg
1kg

38. The more mass an object has, the greater its inertia.

39. stay in motion at a constant velocity unless a net force acts on it.
Newton’s First Law
The Law of Inertia
An object in moving
tends to
stay in motion at a constant velocity
and
an object at rest
remain at rest
unless a net force acts on it.

40. Newton’s First Law

41. Newton’s Second Law of Motion
The Law of Acceleration
A net force acting on an object will accelerate that object in the direction of that force F a

42. FE FE - engine FNet FNet – net force FNet = FE - FF FF FF - friction
Net Force Accelerates
FNet FE FF
FE - engine
FF - friction
FNet – net force
FNet = FE - FF

43. FE=25N FN FN = FE - FF FN = 25N – 5N FN = 20N FF =5N
Net Force Accelerates FN
FE=25N
FF =5N
FN = FE - FF
FN = 25N – 5N
FN = 20N

44. Newton’s Second Law Acceleration
Force = mass x acceleration
F = ma

45. ma
F = F
F a m= m a
F m a=

46. (Assume that there is no friction against the car.)
Example #1
A car with a mass of 2000kg is parked on the side of the road. How much force is needed to accelerate the car at 3m/s²?
(Assume that there is no friction against the car.)

47. Example #1 F

48. Given: m = 2000kg
a = 3m/s²
Find: F = ?
Equation: F = ma
F = (2000kg) x (3m/s²)
F = 15,000N

50. Weight
Weight: The measure of the force of gravity on an object.

51. Mass
Mass: The amount of matter making up an object.

52. Weight
Moon Earth Jupiter
(16.7 lb) (100 lb) (254 lb)

53. Falling

54. { Falling All objects fall at the same rate!! 9.8m/s² Acceleration
due to
Gravity!!! g
32ft/s²
22mph/s

55. W = mg Acceleration due to gravity. g Force due to gravity. W (weight)
Falling
Acceleration
due to
gravity. g
Force
due to
gravity.
W (weight)
W = mg

56. Falling W
W = Fair
Terminal
Velocity
Fair

57. Homework: 12-2
Worksheet: 12-2
Due: 3/10/09

58. Math Practice Page: 367, 1-4 Due: 3/10/09
Homework: 12-3
Math Practice Page: 367, 1-4
Due: 3/10/09

59. A boy pushes forward a cart of groceries with a total mass of 40. 0 kg
A boy pushes forward a cart of groceries with a total mass of 40.0 kg. What is the acceleration of the cart if the net force on the cart is 60.0 N?
Given:
Find:
Equation:
Solve:

60. What is the upward acceleration of a helicopter with a mass of 5000 kg if a force of 10,000 N acts on it in an upward direction?
Given:
Find:
Equation:
Solve:

61. Given: Find: Equation: Solve:
An automobile with a mass of 1200 kg accelerates at a rate of 3.0 m/s2 in the forward direction. What is the net force acting on the automobile? (Hint: Solve the acceleration formula for force.)
Given:
Find:
Equation:
Solve:

62. Given: Find: Equation: Solve:
A 25-N force accelerates a boy in a wheelchair at 0.5 m/s2 What is the mass of the boy and the wheelchair? (Hint: Solve Newton's second law for mass.)
Given:
Find:
Equation:
Solve:

66. Newton’s Third Law Action and Reaction
When one object exerts a force on a second object, the second one exerts a force on the first that is equal in size and opposite in direction.

67. For every action there is an equal and
Action and Reaction
For every action there is an equal and
opposite reaction.

68. Action - Reaction Pair

69. Rocket Propulsion Reaction Force Rocket Accelerates Action Force
Escaping Gases

70. Momentum - Mass on the Move
Momentum ( p unit:kg•m/s )
A property a moving object has because of mass
and velocity.

71. v v

72. momentum = mass X velocity
Momentum Equation
momentum = mass X velocity
p = m x v

73. Example: A car with a mass of 2000 kg is moving with a velocity of 40 m/s. What is its’ momentum?
Given: m = 2000 kg
v = 40 m/s
Find: p = ?
Equation: p = m x v
Solve: p = 2000 kg x 40 m/s
p = 80,000 kg•m/s

74. Conservation of Momentum
The total momentum of a group of
objects does not change unless
outside forces act on the objects.
The momentum before a collision
is equal to the momentum
after the collision.

75. Total Momentum Before = Total Momentum After

76. Total Momentum Before = Total Momentum After

77. Momentum

78. Homework: 12-3
Worksheet: 12-3
Due: 3/12/08

79. Universal Forces d

80. Electromagnetic Forces
Electromagnetic forces are associated with charged particles.

81. Electric Forces

85. Magnetic Force
Magnetic Poles

86. Unlike Poles (North-South)
Attract!!!

87. Like Poles (North-North South-South)
Repel!!!

88. Two forces that act in the nucleus to hold it together.
Nuclear Force
Two forces that act in the nucleus to hold it together.
Strong Nuclear Force
Weak Nuclear Force

89. Strong Nuclear Force Strongest Force Holds the nucleus together
Short Range

90. Weak Nuclear Force
Weaker than the Strong Force
Short Range

91. Gravitational Forces

92. Any object with mass exerts a gravitation force. Long Range
Gravitational Forces
Any object with mass exerts a gravitation force.
Long Range

93. Gravitational Forces

94. Tides

95. Tides

96. Circular Motion

97. Circular Motion V - Velocity Direction of Motion Centripetal Force (g)
Acceleration

98. Sending up Satellites
V = 29,000km/h
(18,000mph)

99. Sending up Satellites
Geostationary

100. Homework: 12-4
Worksheet: 12-4
Due: 3/13/09