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ACCELERATION: C10,S2
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ACCLELERATION
DEFINITION
the rate at which
velocity changes
(includes: speeding up,
slowing down, or
changing directions)
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POSITIVE ACCELERATION
Speeding up; also called
accelerating
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NEGATIVE ACCELERATION
Slowing down; also called
deccelerating
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CHANGE of DIRECTION
Turning, which is a change of
direction, is also acceleration
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FORCE of ACCELERATION
• Acceleration is
always caused by
a force (a push or
a pull on
something).
• For example:
A) What force causes a bicycle to stop?
o Friction caused by brakes pushing on tires
o Friction caused by tires pushing on road 6
FORCE of ACCELERATION,
continued…
B) What force causes a car to turn?
- Friction pushing against the
side of the tires.
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FORCE of ACCELERATION,
continued…
C) What force causes
a rocket to take
off?
- The force of
the exhaust gases
pushing out the
bottom of the
rocket.
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FORMULA of
ACCELERATION
SI Units of ACCELERATION
2
m/s
m/s/s or
or even… km/h/s
** This is because you are
dividing speed (m/s or km/h)
by time (s)
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EXAMPLE - #1
0 km/hr
0 sec
5 km/hr
10 km/hr
1 sec
2 sec
15 km/hr
3 sec
20 km/hr 25 km/hr
4 sec
5 sec
SOLVE FOR ACCELERATION:
The acceleration of a motorcycle is 5 km/hr/sec
(every second, the motorcycle will increase its
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speed by 5 km/hr)
EXAMPLE #2
A man jumps from a plane. His
beginning speed is 100 km/hr SE
(southeast), and his final speed
with his parachute is 10 km/hr SE
(southeast). This took 3 sec.
What was his acceleration?
SOLVE FOR ACCELERATION:
a = Sf – Ss
t
a=?
Sf= 10km/hr
Ss= 100km/hr
t = 3s
a = (10 km/hr – 100 km/hr) = -90km/hr = -30km/hr/s
3s
3s
The negative sign means that he was decelerating (slowing down).
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ACCELERATION REVIEW #1
1) A change in velocity (or
speed) divided by the time it
takes for the change to occur
equals the object’s _______.
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ACCELERATION REVIEW #2
2) Imagine yourself driving a
car down an empty stretch of
road. Describe 3 ways you could
you change your acceleration.
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ACCELERATION REVIEW #3
3) Calculate the acceleration
of a bus whose speed changes
from 6m/s to 12m/s over a
period of 3s.
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ACCELERATION REVIEW #1
ANSWER:
1) The answer is acceleration.
Remember that, like velocity, acceleration has
a direction. A car that takes a turn has
changed its acceleration, even if nothing else
changes.
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ACCELERATION REVIEW #2
ANSWER:
2) You could step on the gas;
you could also step on the brake;
you could turn the wheel, or do
any combination of these.
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ACCELERATION REVIEW #3
ANSWER:
Calculate the acceleration of a bus whose
speed changes from 6m/s to 12m/s over a
period of 3s.
a = Sf – Ss
t
a=?
Sf= 12m/s
Ss= 6m/s t = 3s
a = (12 m/s – 6 m/s)
3s
= 6m/s = 2 m/s/s
3s
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PART 2
Interpreting
Graphs
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Reading Graphs of Acceleration
• You can represent the acceleration of
an object with a speed-time graph
• speed is
plotted on the
vertical axis
(y)
• time is
plotted on the
horizontal
axis (x)
Reading Graphs of Acceleration
• An object
that is
speeding
up will
have a
line that
slopes
upward
(Ex. A)
Reading Graphs of Acceleration
• An object
that is
slowing
down will
have a
line that
slopes
downward
(Ex. C)
Reading Graphs of Acceleration
• A horizontal line represents an acceleration
of zero or constant speed (Ex. B)
Copy Graph Below and Label
ACCELERATION REVIEW #4
4) When reading an
acceleration graph, what
variable will you find on the yaxis? On the x-axis?
HINT: a = Sf – Ss
t
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ANSWER #4
SPEED (y-axis)
&
TIME (x-axis)
a = Sf – Ss
t
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ACCELERATION REVIEW #5
5) What is happening
at point A in this
speed-time graph?
A. the object is
speeding up
B. the object is
slowing down
C. the object is at
rest
D. the object has a
constant speed
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ANSWER #5
Point A =
object is
speeding up
LABEL THIS
ON YOUR
GRAPH
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ACCELERATION REVIEW #6
6) What is happening
at point B in this
speed-time graph?
A. the object is
speeding up
B. the object is
slowing down
C. the object is at
rest
D. the object has a
constant speed
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ANSWER #6
Point B =
object has a
constant
speed
LABEL THIS
ON YOUR
GRAPH
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ACCELERATION REVIEW #7
7) What is happening
at point C in this
speed-time graph?
A. the object is
speeding up
B. the object is
slowing down
C. the object is at
rest
D. the object has a
constant speed
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ANSWER #7
Point C =
object is
slowing down
LABEL THIS
ON YOUR
GRAPH
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