1. Chapter 11: Section 2
Acceleration

2. Acceleration and Motion
Recall that velocity has both a speed and a direction.
Like velocity, acceleration has a value and a direction.
When an object undergoes acceleration, its velocity changes.
acceleration: the rate at which velocity changes over time.

3. An object accelerates if its speed, direction, or both change.
Acceleration can be a change in speed.
An increase or decrease in speed is an acceleration.
Acceleration can also be a change in direction.
A motorcyclist who rides around the inside of a large barrel is constantly accelerating.
A person riding a Ferris wheel at an amusement park is accelerating.

4. Calculating Acceleration

5. Calculating Acceleration
For straight-line motion, a positive acceleration means that the object’s velocity is increasing—the object is speeding up.
Ex. 5.6 m/s2
Negative acceleration means that the object’s velocity is decreasing—the object is slowing down.
Ex m/s2
SI Units for Acceleration: m/s2

6. Let’s Try It!
A flowerpot falls off a second-story windowsill. The flowerpot starts from rest and hits the sidewalk 1.5 s later with a velocity of m/s. Find the average acceleration of the flowerpot.
Given?
Unknown?

7. You Try It!
A lizard accelerates from 2 m/s to 10 m/s in 4 seconds. What is the lizard’s average acceleration?
A runner covers the last straight stretch of a race in 4 s. During that time, he speeds up from 5 m/s to 9 m/s. What is the runner’s acceleration in this part of the race?

8. Graphing Acceleration
The slope of a straight line on a speed vs. time graph is equal to the acceleration.

9. Graphing Acceleration
Acceleration can also be seen on a distance vs. time graph.
The distance vs. time graph is not a straight line when the velocity is not constant.
This curved line indicates that the object is under acceleration.

10. Exit Slip
Identify the straight-line accelerations below as either speeding up or slowing down:
5.7 m/s/s
-29.8 m/s/s
-2.43 m/s/s
9.8 m/s/s