1. Acceleration measures how fast velocity changes.
Section 1.3
Acceleration measures how fast velocity changes.

2. Vocabulary
The rate at which velocity changes with time is called _______________.
acceleration

3. Is acceleration a vector?
YES – it has both size and direction!

4. Acceleration Rule #1 Acceleration in the same ___________ as motion.
direction

5. Acceleration Rule #2
Acceleration in the __________ direction of motion.
opposite

6. Acceleration #3
Acceleration at an ____________ to motion.
angle

7. Am I acceleration?
a. a car slowing down from 50 miles per hour to 40 miles per hour.
b. a car turning a corner.
c. a car starting up again after stopping
YES!
YES!
YES!

8. Thinking Question
Suppose velocity remains steady. Will there be any acceleration? Explain.
No – acceleration is a change in velocity.

9. Calculating Acceleration
a = v final – v initial t
a = acceleration
V initial = initial velocity
V final = final velocity
t = time

10. Class Problem
Mike starts sliding with a velocity of 1 m/s. After 3 seconds, his velocity is 7 m/s. What is his acceleration?
a = 7 m/s – 1 m/s
3 s
a = 6 m/s
3 s
a = 2 m/s2

11. Practice Problem #1
A man walking at 0.5 m/s accelerates to a velocity of 0.6 m/s in 1 second. What is his acceleration?
a = 0.6 m/s – 0.5 m/s
1 s
a = 0.1 m/s
1 s
a = 0.1 m/s2

12. Practice Problem #2
A lady accelerates from a stopped position to 6 m/s in 2 seconds. What is her acceleration?
a = 6 m/s – 0 m/s
2 s
a = 6 m/s
2 s
a = 3 m/s2

13. Bonus Practice Problem
A train traveling at 10 m/s slows down to a complete stop in 20 seconds. What is the acceleration of the train?
a = 0 m/s – 10 m/s
20 s
a = m/s
20 s
a = m/s2
What does a negative sign indicate?
Negative acceleration, otherwise known as slowing down!

14. Thinking Question Which scenario demonstrates negative acceleration?
a. a bird shifts direction in flight
b. an arrow shoots out of a bow
c. an out-of-gas car rolls to a stop
C – because velocity is decreasing!

15. Thinking Question
Suppose you know the initial velocity of a toy airplane taking off and the final velocity when it is cruising high up in the air. Could you calculate the acceleration? Why or why not?
NO – you also need the time interval during which the airplane changed velocity.