Motion and Forces

1
Motion and Forces
2
MOTION
3
S8P3. Students will investigate relationship
between force, mass, and the motion of objects.
a. Determine the relationship between velocity
and acceleration.
4
How are forces and motion related?
5

• A force is a push or a pull that can result in
  motion.
• When a force has been applied to an object and
  the object moves, work is being done.

6
How can motion be described?
7

• By using a reference point A (usually)
  stationary object that helps you detect the
  motion of an object. (Ex. tree, house etc.)

8

• Once the reference point is determined you can
  define motion by speed, position, and direction.

9
What is speed?
10

• Speed refers to how fast an object travels. (Rate
  at which an object moves.)
• Depends on
• Distance
• Time

11

• Various forms of speed
• Instantaneous speed at a given moment
  (speedometer)
• Constant speed that doesnt change (cruise
  control)
• Changing speed that varies (running a mile)

12

• Average speed used when objects are not moving
  at a constant rate.
• Formula
• Speed distance
• time

13

• Ex. If you ran the distance of a football field
  (91 meters) in 30s, would you run the same speed
  from start to finish?
• No, you find the average speed you ran.

14

• s d/t
• s 91m
• 30s
• 3.03 m/s

15
How can you graph speed?
16
Make up a scenario about what's taking place for
each line on the graph
17
Two cars traveled at 50 km/h on the same highway.
After 2 hours the cars are 200 km away from each
other. How is this possible?
THEY HAVE DIFFERENT VELOCITIES
18
What is velocity?
Would you rather know the hurricanes speed or
velocity?
19

• Velocity speed of an object in a particular
  direction.
• Velocity changes when speed or direction of an
  object changes.
• Unit would look like 5 m/s NW

20
Can you have a constant speed but a changing
velocity?
21

• Yes, the Ferris wheel can be moving at a constant
  speed but its constantly changing direction!

22
How is acceleration related to velocity?
23

• Acceleration rate of change of speed (velocity)
• Occurs when an object changes
• Speed
• Direction
• Both

24
What are the types of acceleration?
25

• Positive Acceleration speeding up
• Negative Acceleration slowing down

26
How do you find acceleration?

• Formula
• a vf vi
• t

27
What are velocity/time graphs?

• Shows change in velocity over time (acceleration).

28

Moving at a constant velocity
29

Moving at a positive acceleration velocity
changing at constant rate.
30
Moving at a negative acceleration velocity
changing at constant rate.
31
What is centripetal acceleration?
32

• Acceleration that occurs in a circular motion
  object traveling in a circle is constantly
  changing directions so acceleration occurs
  continuously

33
FORCES
34

• S8P3. Students will investigate relationship
  between force, mass, and the motion of objects.
• b. Demonstrate the effect of balanced and
  unbalanced forces on an object in terms of
  gravity, inertia, and friction.

35
What is a force?
36

• A force is a push or pull that one body exerts on
  another.
• Ex. Friction, gravity, kicking a football.
• Unit Newton (N)

37
What is a net force?
38

• The sum of the forces acting on an object.

39
What is a balanced force?
40

• When the forces acting on the object are equal in
  size and opposite in direction.
• Net force 0 (forces cancel each other out)
• No change in motion occurs!!

41
What is an unbalanced force?
42

• Occurs when forces acting on the object are
  unequal.
• Net Force is in the direction of the larger
  force. (object will move in that direction)

43
What is the difference between balanced and
unbalanced forces?
44
(No Transcript)
45
What is Inertia?
46

• The tendency of an object to resist change.

47
Which has a greater inertia?
48

• Elephant inertia depends on mass!!

49
What is Newtons 1st Law of Motion state?
50

• An object in motion will stay in motion unless an
  outside force acts upon it.
• An object at rest will stay at rest unless an
  outside force acts upon it.

51
What is another name for the 1st Law?

• The Law of Inertia

52
What is the relationship between force, mass, and
acceleration?

53
Force and Acceleration

• The greater the force applied to an object the
  greater the acceleration will be.

54
Force and Mass

• Acceleration will be less on a object that is
  heavier.
• Ex. Softball v. Baseball

55
What does Newtons 2nd Law state?
56

• An object will accelerate in the direction of the
  net force.
• F m x a, a F/m,
• m F/a

57
What is the unit for force?

• Newton
• kg x m/s/s

58
Types of Forces
59
What is a force that opposes motion between 2
moving objects?
60

• FRICTION

61
What does the amount of friction depend on?
62

• 1.Kind of surface
• 2. Force pressing surfaces together.

63
What is static friction?

• Friction between two surfaces that are not moving
  past one another.

64
What is sliding friction?

• Force that opposes motion of 2 objects sliding
  past one another.

65
What is Rolling Friction?

• Opposing motion between two objects rolling past
  each other.

66
How is friction helpful?
67

• Without friction the tires could not push against
  the ground to move the car forward and brakes
  couldnt stop the car.

68
How can you reduce friction?
69

• Lubricants are used to reduce friction.
• Ex. Motor oil, wax, grease
• Switching from sliding to rolling friction
• Ex. Ball bearings between wheel axles

70

• S8P5. Students will recognize characteristics of
  gravity, electricity, and magnetism as major
  kinds of forces acting in nature.
• a. Recognize that every object exerts
  gravitational force on every other object and
  that the force exerted depends on how much mass
  the objects have and how far apart they are.

71
What is Gravity?
72

• A downward force
• Any 2 masses exert an attractive force on each
  other.
• Strength of gravitational force depend on
• 1.) Mass
• 2.) Distance

73
What is the law of universal gravitation?

• All objects are attracted to each by
  gravitational force.
• The larger the object The greater the force
• The closer together the object the greater the
  force.

74
Is weight a force?
75

• Weight is considered to be a gravitational force
  that decreases as you move from Earth.

76
How can you find weight?

• F m x a
• W m x 9.8 m/s/s

77
What is the difference between mass and weight?
78
(No Transcript)
79

• Mass how much matter makes up an object
• (Doesnt change as you move from the Earth to the
  moon.)
• Weight considered to be a gravitational force
• (Decreases as you move from the Earth to the
  moon.)

80
What is acceleration due to gravity?
81

• Anything that falls through the air falls at an
  acceleration of 9.8m/s/s.

82
What is Air Resistance?
83

• Effects anything that is in Earths atmosphere.
• Upward force that opposes gravity of anything
  falling through the air.

84
Air Resistance Depends on 3 things

• 1. SPEED
• 2. SIZE
• 3. SHAPE
• of an object.

85

• If there were no air resistance a hammer and
  feather would fall at the same time.

86
What is a projectile?
87

• Anything that is thrown or shot through the air.

88
Why do projectiles follow a curved path?
89

• They follow a curved path due to pull of gravity.
• Ex An arrow, Bullet, Basketball

90
What is Newtons 3rd Law of Motion?
91

• When one object exerts a force on a second
  object, the second one exerts a force that is
  equal and in size and opposite in direction.
• Action/Reaction Occurs

92
(No Transcript)
93
What is Momentum?
94

• Momentum is related to how much force is needed
  to change an objects motion.
• Momentum mass x velocity
• p m x v

95
What is the law of conservation of momentum?
96

• Momentum can be transferred from one object to
  another

97
What is the relationship between mass and
velocity?

• If two trucks have same velocity, but different
  masses then . . .
• the truck with the larger mass has more momentum