1. Chapter 9 Section 3 Acceleration

2. Acceleration Acceleration = speeding up or slowing down
Acceleration – the rate at which velocity changes
Can be an:
Increase in speed
Decrease in speed
Change in direction

3. Calculating Acceleration
If an object is moving in a straight line
Acceleration (A) = the change in velocity divided by the change in time Or A= v t
Units of acceleration:
m/s2 or mph/s

4. Question
A skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration?

5. A car traveling at 60 mph accelerates to
90 mph in 3 seconds. What is the
car’s acceleration?
Velocity(final) - Velocity(original)
Acceleration =
time
90 mph - 60 mph =
3 seconds
30 mph =
3 seconds =
10 mph/second

6. A car traveling at 60 mph slams on the brakes to
avoid hitting a deer. The car comes to a safe stop
6 seconds after applying the brakes. What is the
car’s acceleration?
Velocity(final) - Velocity(original)
Acceleration =
time
0 mph - 60 mph =
6 seconds
- 60 mph =
6 seconds =
- 10 miles per hour per second

7. Advanced only
Solving for distance when given acceleration and time use the equation: D=(1/2A)(T2) A car advertisement states that a certain car can accelerate from rest to 80 m/s in 8 seconds. Find the car’s average acceleration. What distance did the car travel during this time?

8. Advanced only
When solving for final velocity use the following equation: Vf= AT+Vi Using info from the previous example. If I were to accelerate at this rate for another 60 seconds, how fast would I be going?

9. Graphing Acceleration
Can use 2 kinds of graphs
Speed vs. time
Distance vs. time

10. Graphing Acceleration: Speed vs. Time Graphs
Speed is increasing with time = accelerating
Line is straight = acceleration is constant

11. Graphing Acceleration: Speed vs. Time Graphs
Rise = 4 m/s
Run = 2 s
In Speed vs. Time graphs:
Acceleration = Rise/Run
= 4 m/s ÷ 2 s = 2 m/s2

12. Graphing Acceleration: Distance vs. Time Graphs
On Distance vs. Time graphs a curved line means the object is accelerating.
Curved line also means your speed is increasing. Remember slope = speed.

13. Question Run = 3 s Rise = -6 m/s
Above is a graph showing the speed of a car over time.
1) How is the speed of the car changing (speeding up,
Slowing down, or staying the same)?
2) What is this car’s acceleration?
The car is slowing down
Acceleration = rise/run = -6m/s ÷3s = -2 m/s2

14. curved line = accelerating, flat line = constant speed
Question:
The black and red lines represent a objects that are accelerating. Black is going a greater distance each second, so it must be speeding up. Red is going less each second, so must be slowing down
Remember: in distance vs. time graphs:
curved line = accelerating, flat line = constant speed
Which line represents an object that is accelerating?

15. Question: Hard one
Above is a graph showing the speed of a car over time.
1)What would a distance vs. time graph for this
look like?