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# Acceleration - PowerPoint PPT Presentation

Acceleration. Change in Velocity. 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.

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Presentation Transcript

• 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 – starting velocity velocity

Acceleration= change in velocity

time

90 mph in 3 seconds. What is the

car’s acceleration?

Velocity(final) - Velocity(original)

=

Acceleration

time

90 mph - 60 mph

=

3 seconds

30 mph

=

3 seconds

=

10 mph/second

Positive acceleration

Negative acceleration

avoid hitting a deer. The car comes to a safe stop

6 seconds after applying the breaks. What is the

car’s acceleration?

Velocity(final) - Velocity(original)

=

Acceleration

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 non-linear velocity-time graph (rise/run) will predict an objects instantaneous acceleration. a = v/t

Free fall linear slope (rise/run).

• 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 linear slope (rise/run).

• 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

t = 0 linear slope (rise/run).

t = 1 second

t = 2 seconds

t = 3 seconds

Galileo

Acceleration= change in velocity

time

Galileo linear slope (rise/run).

• Same things happen when things fall

• Didn’t drop things from Tower of Pisa

v linear slope (rise/run). 2final = 2gdy

• A final velocity can be calculated over a vertical displacement “dy" during free fall using the equation:

d linear slope (rise/run). y = 1/2 gt2

• The vertical displacement “dy" that occurs during a specific time of free fall can be determined using the equation:

• Or a time interval can also be determined over a specified distance of freefall using the equation:

t2 = 2dy /g

Falling linear slope (rise/run).

• 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.

Terminal velocity linear slope (rise/run).

• Force of gravity is constant

• air resistance increases as you speed up

• until the force is equal

• Equal forces, no acceleration

• constant velocity terminal velocity