Section 1.3

Acceleration measures how fast velocity changes.

Vocabulary

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

Is acceleration a vector?

YES – it has both size and direction!

Acceleration Rule #1

Acceleration in the same ___________ as motion.

direction

Acceleration Rule #2

Acceleration in the __________ direction of motion.

opposite

Acceleration #3

Acceleration at an ____________ to motion.

angle

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!

Thinking Question

Suppose velocity remains steady. Will there be any acceleration? Explain.

No – acceleration is a change in velocity.

Calculating Acceleration

a = v final – v initial

t

a = acceleration

V final = final velocity

V initial = initial velocity

t = time

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 sa = 2 m/s2

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

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

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 = -10 m/s

20 s

a = - 0.5 m/s2

What does a negative sign indicate?

Negative acceleration, otherwise known as slowing down!

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!

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.