1. Describing Motion Ch. 3 & 4 Motion & Forces Motion & Speed (3.1)
Velocity (3.2)
Acceleration (3.2)

2. Newton’s First Law Newton’s First Law of Motion
An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force.
motion
constant velocity
net force

3. Motion 3.1 Problem: Is your desk moving? We need a reference point...
nonmoving point from which motion is measured

4. Motion Motion Change in position in relation to a reference point.

5. Motion
Problem:
You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward.
You have mistakenly set yourself as the reference point.

6. Speed
Speed
rate of motion
distance traveled per unit time

7. Speed
Instantaneous Speed
speed at a given instant
Average Speed

8. Calculations d = 100 m v = d ÷ t t = 20 s v = (100 m) ÷ (20 s) v = ?
Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster?
GIVEN:
d = 100 m
t = 20 s
v = ?
WORK:
v = d ÷ t
v = (100 m) ÷ (20 s)
v = 5 m/s
You skate faster!

9. Calculations
Florence Griffith Joyner set a world record by running 200 m in 21.34s. What was her average speed?
Answer: 9.37 m/s

10. Calculations v = 330 m/s t = d ÷ v d = 1km = 1000m
Sound travels 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for you to hear it?
GIVEN:
v = 330 m/s
d = 1km = 1000m
t = ?
WORK:
t = d ÷ v
t = (1000 m) ÷ (330 m/s)
t = 3.03 s

11. Work the practice problem p. 67
Answer: 21.9s

12. Graphing Motion slope = speed steeper slope = straight line =*
07/16/96
Graphing Motion
Distance-Time Graph A B
slope =
steeper slope =
straight line =
flat line =
speed
faster speed
constant speed
no motion *

13. Graphing Motion Who started out faster? A (steeper slope)
Distance-Time Graph A B
Who started out faster?
A (steeper slope)
Who had a constant speed? A
Describe B from min.
B stopped moving
Find their average speeds.
A = (2400m) ÷ (30min) A = 80 m/min
B = (1200m) ÷ (30min) B = 40 m/min

14. Design a Slow Flyer p. 70
You will be designing a paper air plane to fly as slow as possible
Form a hypothesis
What factors might contribute to a slow flying plane?
How will we calculate the speed?
Design a set of rules
Flight location, distance, launching method…

15. Velocity and Acceleration
p. 72

16. 3.2 Speed & Velocity Problem:
A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried?
It depends on the storm’s direction!

17. Speed & Velocity Velocity speed in a given direction
can change even when the speed is constant!

18. Acceleration Acceleration the rate of change of velocity
change in speed or direction
a: acceleration
vf: final velocity
vi: initial velocity
t: time

19. Acceleration Positive acceleration “speeding up” Negative acceleration
“slowing down”

20. Calculation s a = (vf - vi) ÷ t t = 3 s a = (32m/s - 10m/s) ÷ (3s)
A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration?
GIVEN:
vi = 10 m/s
t = 3 s
vf = 32 m/s
a = ?
WORK:
a = (vf - vi) ÷ t
a = (32m/s - 10m/s) ÷ (3s)
a = 22 m/s ÷ 3 s
a = 7.3 m/s2

21. Calculations t = ? t = (vf - vi) ÷ a t = (0m/s-30m/s)÷(-3m/s2)
How long will it take a car traveling 30 m/s to come to a stop if its acceleration is m/s2?
GIVEN:
t = ?
vi = 30 m/s
vf = 0 m/s
a = -3 m/s2
WORK:
t = (vf - vi) ÷ a
t = (0m/s-30m/s)÷(-3m/s2)
t = -30 m/s ÷ -3m/s2
t = 10 s

22. Graphing Motion
Distance-Time Graph
Acceleration is indicated by a curve on a Distance-Time graph.
Changing slope = changing velocity

23. Graphing Motion acceleration slope = + = speeds up - = slows down
Speed-Time Graph
acceleration
+ = speeds up
- = slows down
slope =
straight line =
flat line =
constant accel.
no accel. (constant velocity)

24. Graphing Motion Specify the time period when the object was...
Speed-Time Graph
Specify the time period when the object was...
slowing down
5 to 10 seconds
speeding up
0 to 3 seconds
moving at a constant speed
3 to 5 seconds
not moving
0 & 10 seconds

25. Defining Force (3.4) Forces Friction
Ch. 3.4 Motion & Forces
Defining Force (3.4)
Forces
Friction

26. Force Video Before the video: Complete the pretest During the video:*
07/16/96
Force Video
Before the video:
Complete the pretest
During the video:
Complete the video review
After the video:
Complete the post test
VL Force newton.pdf and video *

27. Force Video

28. Force Fkick Fgrav Force a push or pull that one body exerts on another
What forces are being exerted on the football?
Fkick
Fgrav

29. Force
Balanced Forces
forces acting on an object that are opposite in direction and equal in size
no change in velocity

30. Balanced Forces

31. Force Net Force unbalanced forces that are not opposite and equal
velocity changes (object accelerates)
Fnet
Ffriction
Fpull N W

32. 10N-7N = 3N causes change in velocity.
Net Force - Unbalanced
10 N
7 N
Net Force
10N-7N = 3N causes change in velocity.

33. Newton’s First Law Newton’s First Law of Motion
An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force.

34. Newton’s First Law Newton’s First Law of Motion “Law of Inertia”
tendency of an object to resist any change in its motion
increases as mass increases

35. Which has more inertia?

36. Friction Friction force that opposes motion between 2 surfaces
depends on the:
types of surfaces
force between the surfaces

37. Friction Friction is greater... between rough surfaces
when there’s a greater force between the surfaces (e.g. more weight)
Pros and Cons?

38. Gravity/Weight
3.5

39. Gravity
Gravity
force of attraction between any two objects in the universe
increases as...
mass increases
distance decreases

40. Gravity
Who experiences more gravity - the astronaut or the politician?
Which exerts more gravity - the Earth or the moon?
more mass
less distance

41. Weight The measure of the force of gravity on an object
Not the same as mass
Your mass would be the same on the moon but your weight would be less!

42. Weight Mass- the amount of matter in an object Measured in kg
Weight is a force
Measured in newtons (N)
1 kg of mass on earth’s surface weighs 9.8N

43. Gravity Would you weigh more on Earth or Jupiter? Jupiter because...
greater mass
greater gravity
greater weight