1. Acceleration
Physical Science

2. What we are going to do?
For those classes that need to finish walking the graphs, you will do so
Questions about Homework handout #2
Formal introduction of acceleration
Questions about book homework

3. Acceleration
Anytime the velocity of an object changes, the object accelerates
If the motion of object changes direction

4. Velocity changes if…
Speeding up
Slowing down

5. Velocity changes if…
The direction of the motion changes, but the speed does not
This type of acceleration is call centripetal acceleration

6. Calculating acceleration
Use for only 1-dimensional acceleration
Acceleration = change in velocity / time
a = ∆v / t

7. ∆v ∆v = vf - vi The ∆ means the change in…
You find the change in a value by subtracting it initial value from its final value
∆v = final velocity – initial velocity
∆v = vf vi

8. Equation for average acceleration
a = (vf - vi) / t
vf = final velocity
vi = initial velocity
t = elapsed time
a = acceleration

9. Ex #1
A flowerpot falls off a second story windowsill. The flowerpot start from rest and hits the sidewalk 1.5 s later with a velocity of 14.7m/s. Find the average acceleration.

10. What information is given? Identify the information.
Is the time
14.7 m/s
is the final velocity
Starts from rest
Means that the initial velocity is zero (0)
“at rest” always means that vi = o

11. Answer #1 a = (14.7 – 0) / 1.5 = 9.8 What are the units?
(14.7 m/s – 0 m/s) 1.5 s = (m/s) / s
m / s2

12. Units
How do you simplify
(¾) / 9

13. answer

14. How we get m/s2 for units of acceleration

15. Ex #2
While driving at an average velocity of 15.6 m/s down the road, a driver slams on brakes to avoid hitting a squirrel. The car stops completely in 4.2 seconds. What is the acceleration of the car?

16. What you want to solve for
Givens
15.6 m/s = vi
4.2 s = t
0 = vf
What you want to solve for
acceleration

17. Solution
a = (0 – 15.6) / 4.2 = (-3.7) m/s2

18. Ex #3
If a bicycle has an average acceleration of m/s2, and its initial forward velocity is 8.2 m/s, how long will it take the cyclist to bring the bicycle to a complete stop?

19. Answer Givens: Solution: (-0.44m/s2) = a (8.2 m/s) = vi (0 m/s) = vf
( 8.2 – 0) / t = (-.44)  8.2 / t = (-.44) / 1
Cross multiply: 8.2 = (-.44) t
Divide: 8.2 / (-.44) = -19 s