1. Describing Motion
Words
Drawings
Graphs
Equations

2. Distance or Displacement?
Distance – how much ground the object has covered (what would the odometer say?)
Distance = 12 m
Displacement – how far out of place the object is (how far are you from home?)
Displacement = 0 m

3. Ticker Tape Diagrams (a.k.a. Car with oil leak)
Distance between dots represents the object's
position change during that time interval
Time interval is the same, but the distance traveled may change
Why?

4. Water Drop Demo

5. Fast or Slow?
A large distance between dots indicates that the object was moving fast during that time interval.
A small distance between dots means the object was moving slowly during that time interval.

6. Speed vs. Velocity
Speed: the rate of change of position, the rate at which an object moves.
Velocity: the speed in a certain direction

7. Acceleration Acceleration: the rate of change of velocity.
An object accelerates if its speed changes or if its direction changes
For the examples in this ppt, we assume that there is no change in direction.

8. Constant Velocity or Acceleration?
The same distance between dots means that the velocity is constant (not changing)
A changing distance between dots means that the object is accelerating (changing velocity)

9. What’s happening with velocity and acceleration?
1) ) ) )

10. Constant Velocity Constant Velocity – How do we know?
Same distance between cars for each time interval
How fast is the car going?
v = d/t = 10 m / 1 s = 10 m/s

11. Constant Velocity / P-t Graph
Now, let’s put the time data on the x-axis of an x-y graph and move the position data to the y-axis.
Constant Velocity
Line on position time graph is straight with a constant slope

12. Changing Velocity
Consider a car moving right with a changing velocity.
Is the velocity increasing or decreasing?
Increasing
Is the car accelerating?
Yes
Now, put the data on an x-y graph

13. Changing Velocity/ P-t Graph
Increasing velocity
Acceleration
Line on the position time graph is curved
The line is getting steeper (slope is increasing)

14. Slope of P-t Graph = Velocity
Constant Velocity
No acceleration
Changing Velocity
+Acceleration

15. Using Slope to Describe Motion

16. Calculating Velocity v = d/t (this can be rearranged d=vt, t=d/v)
Since velocity = slope of P-t Graph, we can calculate velocity using:
velocity = slope = rise = Δdistance
run Δtime
v = d/t (this can be rearranged d=vt, t=d/v)
If a car goes 50 meters in 10 seconds, than v = 50 m/10 s = 5 m/s

17. Velocity Practice Problems
A boy runs a 5 km race in 25 minutes. What is his velocity?
A bird flew for 60 seconds at 3 m/s. How far did it fly?
A car drove 200 km at 30 km/hour. How long was the car driving?

18. Velocity and Acceleration
Constant velocity
No Acceleration
Acceleration = Slope of v-t graph = 0

19. Velocity and Acceleration
Changing velocity
Accelerating
Acceleration = slope of v-t graph

20. Calculating Acceleration
Since acceleration is the slope of the v-t Graph, we can calculate acceleration using:
a = slope = rise = Δv = vf – vi
run Δt t
a = vf – vi where vf = final velocity
t and vi = initial velocity
and t = time

21. Calculating Acceleration

22. Comparing Velocity and Acceleration
Constant Velocity
Changing Velocity

23. Motion 3-2-1 Review 3 Things you learned about motion
2 Things you already knew about motion
1 Question you have about motion