1. Physical Science Chapter 11
Motion
Physical Science
Chapter 11

2. Physical Science chapter 11
Motion
Can be described as a change in position.
Physical Science chapter 11

3. Distance vs. displacement
Distance is how far you traveled
What your odometer reads
Displacement is the distance between your starting point and your ending point, regardless of your path
As the crow flies
Physical Science chapter 11

4. Physical Science chapter 11
Speed
How fast something moves
The rate of change in position
The rate of motion
Rate means change over time
Physical Science chapter 11

5. Physical Science chapter 11
Velocity vs. speed
Velocity describes both speed and direction.
Both “how fast” and “which way” something is moving
Physical Science chapter 11

6. Physical Science chapter 11
Constant speed
Speed that does not vary
Cruise control
Physical Science chapter 11

7. Physical Science chapter 11
Average speed
Total distance traveled divided by total time of travel
Used when the object in motions makes changes in speed, including starts and stops.
Physical Science chapter 11

8. Physical Science chapter 11
Calculating speed
If you know distance and time, you can calculate average speed.
Physical Science chapter 11

9. Physical Science chapter 11
Example
You skate a distance of 100 m in s. What is your average speed?
Known:
d = 100 m
t = 67 s
Unknown
v = ?
Physical Science chapter 11

10. Physical Science chapter 11
Example continued
Physical Science chapter 11

11. Physical Science chapter 11
You try
Find the speed in meters per second of a baseball thrown 38 m from third base to first base in 1.7 s.
Physical Science chapter 11

12. Physical Science chapter 11
Example
Find the velocity in meters per second of a swimmer who swims 110 m toward the shore in 72 s.
Physical Science chapter 11

13. Physical Science chapter 11
You try
Calculate the displacement in meters that a cyclist would travel in h at an average velocity of 12.0 km/h to the southwest. Remember to include direction.
Physical Science chapter 11

14. Physical Science chapter 11
Instantaneous speed
The rate of motion at a given instant
Speedometer
Physical Science chapter 11

15. Physical Science chapter 11
Graphing speed
When distance is graphed on the y-axis and time is graphed on the x-axis, we call this a distance-time graph.
The slope of a distance-time graph is the speed.
See pages 370–371
Discuss the practice problems
Physical Science chapter 11

16. Physical Science chapter 11
Acceleration
The rate of change of velocity.
Acceleration occurs if either the speed or direction changes, or if both change.
“Slowing down” is a change in speed, so when something slows down, it is accelerating.
Physical Science chapter 11

17. Physical Science chapter 11
Acceleration
The size of acceleration depends on both the change in velocity and the time interval over which the change takes place
If the change in velocity is large, the acceleration will be large.
If the time interval is short, then acceleration will be large.
Physical Science chapter 11

18. Calculating acceleration
The triangle is the Greek letter delta, and stands for “change in”
Physical Science chapter 11

19. Physical Science chapter 11
Units on acceleration
Written as m/s2
Physical Science chapter 11

20. Physical Science chapter 11
Examples
Natalie accelerates her skateboard along a straight path from 0.0 m/s to 4.0 m/s in 2.5 s. Find her average acceleration.
Find the average acceleration of a northbound subway train that slows down from 12. m/s to 9.6 m/s in 0.8 s.
Physical Science chapter 11

21. Acceleration on graphs
On a speed vs. time graph (speed on the y-axis and time on the x-axis)
Acceleration is the slope
On a distance vs. time graph (distance on the y-axis and time on the x-axis)
A curved line indicates acceleration
A straight line indicates a constant velocity (no acceleration)
Physical Science chapter 11

22. Physical Science chapter 11
Discuss
Identify the straight-line accelerations below as either speeding up or slowing down
5.7 m/s2
-29.8 m/s2
-2.43 m/s2
9.8 m/s2
A turtle swimming in a straight line twoard shore ahs a speed of 0.50 m/s. After 4.0 s, its speed is 0.80 m/s. What is the turtle’s average acceleration?
Physical Science chapter 11

23. Physical Science chapter 11
Force
A push or a pull one object exerts on another
Physical Science chapter 11

24. Physical Science chapter 11
Fundamental forces
Gravity
Electromagnetic force
Like charges repel; opposite charges attract
Strong force
Holds nucleus together
Weak force
Involved with radioactivity
Physical Science chapter 11

25. Contact forces vs. field forces
Objects must be touching
Field forces
Don’t need to be touching
Gravity, magnets, electric charges
Physical Science chapter 11

26. Physical Science chapter 11
Balanced forces
Forces that are equal in size and opposite in direction are called balanced forces.
Tug-of-war tie
Physical Science chapter 11

27. Physical Science chapter 11
Net Force
When forces are unbalanced, there is a net force.
A net force always causes a change in velocity.
Could be a change is speed, a change in direction, or both.
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28. Physical Science chapter 11
Friction
The force that opposes motion between two surfaces that are touching each other.
Enables us to walk, hold things, etc.
Physical Science chapter 11

29. Physical Science chapter 11
Friction
The amount of friction depends on two things
The kinds of surfaces
The force pressing the surfaces together
More force  more friction
Physical Science chapter 11

30. Physical Science chapter 11
Static Friction
Between surfaces that aren’t moving
Largest frictional force between any two objects
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31. Physical Science chapter 11
Kinetic Friction
Friction between moving surfaces
Sliding friction
Rolling friction
Usually less than sliding friction
Physical Science chapter 11

32. Physical Science chapter 11
Discuss
What is a force?
What are balanced forces?
What is friction?
Does a net force of zero mean that there is no force at all?
Physical Science chapter 11