1. Acceleration

2. Bell Ringer
Sports announcers will occasionally say that a person is accelerating if he/she is moving fast. Why is this not an accurate description of what acceleration is?

3. Objectives Define acceleration in words and with an equation
Identify positive and negative acceleration by analyzing a graph
Calculate acceleration with the use of an equation and graph
Define and apply the force of gravity

4. Change in Velocity
Each time you take a step you are changing the velocity of your body.
You are probably most familiar with the velocity changes of a moving bus or car.
The rate at which velocity (speed or direction) changes occur is called acceleration.

5. Change in velocity = final – starting velocity velocity
Acceleration= final velocity- starting velocity
time
Change in velocity = final – starting velocity velocity
Acceleration= change in velocity

6. 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

7. Positive acceleration Negative acceleration

8. A car traveling at 60 mph slams on the breaks to
avoid hitting a deer. The car comes to a safe stop
6 seconds after applying the breaks. 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

9. Calculate the instantaneous acceleration of the graph:
- A constant acceleration produces a straight line or linear slope (rise/run). - The slope of a non-linear velocity-time graph (rise/run) will predict an objects instantaneous acceleration. a = v/t
Calculate the instantaneous acceleration of the graph:
a = v/t
a = 4m/s / 1s
a = 4m/s2

10. Free fall
The constant acceleration of an object moving only under the force of gravity is "g".
The acceleration caused by gravity is 10 m/s2
If there was no air, all objects would fall at the same speed
Doesn’t depend on mass
After 1 second falling at 10 m/s
After 2 seconds 20 m/s
3 seconds 30 m/s

11. Galileo 1600’s Studied how things fell Didn’t have a good clock
Rolled balls down an inclined plane
Found that the speed increased as it rolled down the ramp

12. Galileo Acceleration= change in velocity time t = 0 t = 1 second
t = 2 seconds
t = 3 seconds

13. Galileo Same things happen when things fall
Didn’t drop things from Tower of Pisa

14. Falling Air resistance will increase as it falls faster
An upward force on the object
Eventually gravity will balance with air resistance
Reaches terminal velocity - highest speed reached by a falling object.

15. Terminal velocity Force of gravity is constant
air resistance increases as you speed up
until the force is equal
Equal forces, no acceleration
constant velocity terminal velocity

17. Positive Velocity and Positive Acceleration

18. Positive Velocity and Negative Acceleration

19. Negative Velocity and Negative Acceleration

20. Negative Velocity and Positive Acceleration