1. 12.1 Acceleration

2. Acceleration Acceleration
A vector that changes speed or direction or both.
When a object changes velocity
Measured in m/s2
Acceleration may be positive, negative or zero.
Positive acceleration causes an object to speed up
Negative acceleration causes an object to slow down
Zero acceleration is an object is at rest or moving with constant speed or velocity

3. Acceleration Acceleration
Acceleration may be positive, negative or zero
Positive acceleration causes an object to speed up
Negative acceleration causes an object to slow down
Zero acceleration is an object is at rest or moving with constant speed or velocity

4. How is acceleration occurring??

5. Calculating Acceleration
Acceleration = Change in velocity Total Time Acceleration = (vf – vi) t Vf = final velocity Vi = initial velocity t = time

6. Acceleration
Example #1 A ball at rest, on the top of a ramp, starts rolling down the ramp. After 2 seconds, its velocity is 6 m/s. What is the acceleration of the ball?

7. Acceleration
Example #2 While traveling along a highway a driver slows from 24 m/s to 15 m/s in 12 seconds. What is the automobile’s acceleration?

8. Acceleration
Example #3 A parachute on a race car opens and changes the speed of the car from 50 m/s to 15 m/s in a period of 7.3 seconds. What is the acceleration of the car?

9. Free Fall 1600’s Studied how things fell Didn’t have a good clock
Galilei 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
1st person to explain acceleration of moving objects and falling bodies.

10. Free Fall Acceleration Due to the Earth’s Gravity
Galileo
When dropped, these two different masses will fall with the same acceleration!

11. Free Fall - Falling Objects
When gravity is the only force acting on an object (free fall acceleration) is directed toward the center of the earth.
For free fall, it is customary to use the letter g to represent the acceleration because the acceleration is due to gravity.
Although g varies slightly in different parts of the world, its average value is nearly 9.8 m/s2 (This number is VERY important, remember it!!)

12. Free Fall – All objects fall at the same rate
If you drop a coin and a feather at the same time you will notice that the coin reaches the ground way before the feather. Why???
However, if you were to take the air out of the container (vacuum) you would find that the coin and feather fall together and hit the bottom at the same time!

13. Free Fall – Air Resistance
In Air:
A stone falls faster than a feather
Air resistance affects stone less
In a Vacuum:
A stone and a feather will fall at the same speed.
Thinker:
What does it means if you were on the moon and the acceleration due to gravity is 1.62 m/s2?

14. Videos

15. Free Fall
The constant acceleration of an object moving only under the force of gravity is "g".
The acceleration caused by gravity is 9.8 m/s2
If there was no air (Vacuum), all objects would fall at the same speed
Doesn’t depend on mass

16. Speed-Time Graph
The slope of a speed-time graph equals the acceleration of the object

17. Speed-Time Graph What is the acceleration of A?
What is the acceleration of B?
What is the acceleration of C?

18. 11.6 Assessment
Question #1 Describe three types of changes in velocity which creates acceleration.

19. 11.6 Assessment
Question #2 What is the equation for acceleration?

20. 11.6 Assessment
Question #3 What shows acceleration on a speed-time graph?

21. 11.6 Assessment
Question #4 What is the acceleration of an object moving at a constant speed?