Transcript Acceleration

Change in Velocity
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Each time you take a step you
are changing the velocity of
your body.
You are probably most familiar
with the velocity changes of a
moving bus or car.
The rate at which velocity
(speed or direction) changes
occur is called acceleration.
Acceleration= final velocity- starting velocity
time
Change in velocity = final
velocity
–
Acceleration= change in velocity
time
starting
velocity
A car traveling at 60 mph accelerates to
90 mph in 3 seconds. What is the
car’s acceleration?
Acceleration
=
Velocity(final) - Velocity(original)
time
=
=
90 mph - 60 mph
3 seconds
30 mph
3 seconds
= 10 mph/second
Positive
acceleration
Negative
acceleration
A car traveling at 60 mph slams on the breaks to
avoid hitting a deer. The car comes to a safe stop
6 seconds after applying the breaks. What is the
car’s acceleration?
Acceleration =
Velocity(final) - Velocity(original)
time
=
=
0 mph - 60 mph
6 seconds
- 60 mph
6 seconds
= - 10 miles per hour per second
- A constant acceleration
produces a straight line or
linear slope (rise/run).
- The slope of a nonlinear velocity-time graph
(rise/run) will predict an
objects instantaneous
acceleration.
a = v/t
Free fall
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The constant acceleration of an
object moving only under the
force of gravity is "g".
The acceleration caused by
gravity is 10 m/s2
If there was no air, all objects
would fall at the same speed
Doesn’t depend on mass
After 1 second falling at 10 m/s
After 2 seconds 20 m/s
3 seconds 30 m/s
Galileo
 1600’s
 Studied
how things fell
 Didn’t have a good clock
 Rolled balls down an
inclined plane
 Found that the speed
increased as it rolled
down the ramp
Galileo
Acceleration= change in velocity
time
t=0
t = 1 second
t = 2 seconds
t = 3 seconds
Galileo
Same
things happen when things fall
 Didn’t drop things from Tower
of Pisa
A
final velocity can be calculated
over a vertical displacement “dy"
during free fall using the equation:
2
v final
= 2gdy
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The vertical displacement “dy" that
occurs during a specific time of free fall
can be determined using the equation:
dy = 1/2

2
gt
Or a time interval can also be
determined over a specified distance
of freefall using the equation:
2
t =
2dy /g
Falling
Air resistance will
increase as it falls faster
 An upward force on the
object
 Eventually gravity will
balance with air
resistance
 Reaches terminal velocity
- highest speed reached
by a falling object.
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Terminal velocity
 Force
of gravity is constant
air resistance increases as
you speed up
 until the force is equal
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Equal forces, no
acceleration
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constant velocity
terminal velocity