1. Chp. 4: Speed, Velocity, and Acceleration
Study Guide

2. Average Speed
Total distance traveled divided the total time taken to travel that distance.
Speed=Distance/Time
Ex: A soccer ball takes 60 seconds to roll 30 meters.
Average speed=30 meters/60 sec=0.5 m/s

3. Practice Problem
The workers placed 125 meters of asphalt in 2.5 hours. What was their average speed?
 Answer: 50 m/hr
Formula: S = D  T
Equation: S = 125  2.5
S = 50 m/hr

4. Formula If you need to find speed (distance/time)
If you need to find time (distance/speed)
If you need to find distance (speed x time)
Formula Fact Triangle

5. Velocity The speed and direction of a moving object.
Ex. 200 m/s West (speed and direction)
There are 3 things that can change velocity
1. Change in speed
2. Change in direction
3. Change in both

6. Changes in Velocity
Ex. A car is on a curving road, so velocity is changing. As long as you’re turning, the velocity is changing.
Ex. A car is moving and then stops at a stop light. Because the car’s speed changed, the velocity changed.

7. Acceleration A change in velocity during a period of time.
Acceleration=change in speed/time= m/s2
When you’re speeding up your velocity and your acceleration move in the same direction
When you’re slowing down, your velocity and your acceleration move in opposite directions.

8. Acceleration cont.
If time and speed change you have to find the differences of highest data point and lowest data point of the two.
Ex. Times (sec)=1, 2, 3, 4, 5
Difference=5-1=4 sec
Velocity (m/sec, N)=2, 2.5, 3, 3.5, 4
Difference=4-2=2 m/s N
Acceleration=2/4=0.5m/s2

9. Practice Problem
During a bike race, a cyclist accelerates to the north from 8 meters per second to 10 meters per second in 5 seconds to finish the race. What is his acceleration?
Formula: final speed-initial speed
Time
10 m/s – 8 m/s = 2 m/s = 0.4 m/s2
5 seconds sec

10. Distance-Time Graphs A graph comparing distance and time.
X-axis=time, Y-axis=distance

11. Example of Distance-Time Graph
When speed is constant, distance and time are increasing at the same rate.

12. Example of Distance-Time Graph
When the graph line is flat (horizontal), the object is not moving. Time is going by, but distance is not increasing.

13. Example of Distance-Time Graph
When the graph line is curved upward, the object’s speed is increasing because distance is increasing faster than time.

14. Example of Distance-Time Graph
When the graph line is curved downward towards a flat line, the object’s speed is decreasing because time is increasing faster than distance.
Decreasing speed can also look like this

15. Example of Distance-Time Graph
The steeper the slope of the graph line, the faster the speed.
faster
slower