1. Motion
Chapter 11

2. Observing Motion How do you determine if something is moving?
Is a person sitting in a driving car moving?
If the earth is orbiting the sun, ARE YOU MOVING NOW?

3. Observing Motion
Motion: an object changes position with respect to a reference point
Frame of Reference: describes the motion of an object relative to reference points
An object is in motion if it changes position with respect to a reference point

4. Observing Motion
Motion can be described in terms of distance, position, displacement, speed, velocity, acceleration, and time
Scalar: Quantities that are described by a magnitude (numerical value) only
Speed, distance
Vector: Quantities that can be described by a magnitude (number) and direction
Displacement, velocity, acceleration

5. Observing Motion
Distance: scalar quantity that measures the path taken
Displacement: vector quantity that measures object’s overall change in position, how out of place it is, always includes direction

6. Speed
Speed: scalar, refers to how fast an object is moving – how fast it is covering distance
Constant Speed: equal distances in equal amounts of time
Instantaneous Speed: the speed at any given time
Average speed is calculated as total distance divided by total time  v = d/t
The SI unit for speed is meters per second (m/s) – smaller units = more precise!
You cannot have negative speed

7. Velocity
Velocity: vector, measures rate at which an object changes position AND in which direction (speed + direction!)
Velocity can be described as north, south, east, west, as positive/negative depending on the direction of the motion
Up, forward, and right are usually positive
Down, backwards, and left are usually negative
Zero velocity means the object is at rest

8. Velocity Constant Velocity: same displacement for each time interval
Instantaneous Velocity: velocity at any given time
Equation and units are the same as speed, however your final answer should include a direction!
If you take a step forward and then back, your velocity is 0 because the motion has no change in position

9. Intervals Interval: space between
Time (s)
Total distance (m)
Average speed (m/s)
1.0 4
2.0 10
3.0 18
4.0 27
5.0 37
6.0 48
7.0 59
8.0 71
9.0 83
10.0 96
10.3
100
Interval: space between
Speed and acceleration can be calculated from given intervals
How much time has passed between the first and second lines? How much distance was covered between these two times?
Between 1 and 2 = 1 second
Between 4 and 10 = 6 meters
6/1 = 6 m/s

10. Graphing Motion
Speed is shown with a position (distance) vs. time graph (p-t)
In a p-t graph, distance is a function of time – slope represents the speed

11. What object could have this type of motion?

12. What object could have this type of motion?

13. Acceleration
Acceleration: vector, measures how much an object’s velocity is changing during a given time (usually 1 second)
Change in speed, direction, or both
Acceleration can be positive or negative
High acceleration: Speeding up or slowing down very quickly, low acceleration: speeding up or slowing down slowly

15. Acceleration
If an object is still, or the object’s velocity is not changing, the object is not accelerating
If an object is moving at a constant speed in a circle, the speed is not changing, but direction (velocity) is, the object is accelerating
High Acceleration: Speeding up or slowing down, very quickly
Low Acceleration: Speeding up or slowing down, slowly

16. Acceleration
Centripetal Acceleration: acceleration that occurs in circular motion
Constant Acceleration: when an object’s velocity changes at a constant amount each second

17. Acceleration
To calculate acceleration, subtract the initial velocity (vi) from final velocity (vf) and divide by time
a = vf – vi or a = v
t t
 is called a delta, it means change
The SI unit for acceleration is m/s2 (m/s/s)

18. Graphing Motion
Acceleration is shown with a velocity vs. time graph (v-t)
In a v-t graph, velocity is a function of time – slope represents the acceleration
How to read and interpret graphs

19. Intervals
As before, you can use a motion graph to calculate speed or acceleration during a specific interval
What is the acceleration from points D to E?

20. What object could have this type of motion?

21. What object could have this type of motion?