Acceleration

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Acceleration
2
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.

3

• Acceleration final velocity- starting velocity
• time
• Change in velocity final
  starting velocity velocity
• Acceleration change in velocity
• time

4
A car traveling at 60 mph accelerates to 90 mph
in 3 seconds. What is the cars acceleration?
Velocity(final) - Velocity(original)

Acceleration
time
90 mph - 60 mph

3 seconds
30 mph

3 seconds

10 mph/second
5
Positive acceleration
Negative acceleration
6
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 cars acceleration?
Velocity(final) - Velocity(original)

Acceleration
time
0 mph - 60 mph

6 seconds
- 60 mph

6 seconds

- 10 miles per hour per second
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• - 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

8
Free fall

• 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
• Doesnt depend on mass
• After 1 second falling at 10 m/s
• After 2 seconds 20 m/s
• 3 seconds 30 m/s

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Galileo

• 1600s
• Studied how things fell
• Didnt have a good clock
• Rolled balls down an inclined plane
• Found that the speed increased as it rolled down
  the ramp

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Galileo
Acceleration change in velocity time
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Galileo

• Same things happen when things fall

• Didnt drop things from Tower of Pisa

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v2final 2gdy

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

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dy 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
14
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

• Equal forces, no acceleration

• constant velocity terminal velocity