Transcript Section 1.3

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

direction
Acceleration in the same ___________
as motion.
Acceleration Rule #2

opposite
Acceleration in the __________
direction
of motion.
Acceleration #3

angle
Acceleration at an ____________
to
motion.
Am I acceleration?
a. a car slowing down from 50 miles per
hour to 40 miles per hour. YES!
b. a car turning a corner. YES!
c. a car starting up again after stopping
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
3s
a = 6 m/s
3s
a = 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
1s
a = 0.1 m/s
1s
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
a = 6 m/s
2s
2s
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
a = -10 m/s
20 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?
– you also need the time interval
during which the airplane changed velocity.
NO