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Acceleration After Applied Force is Stopped?

  1. May 16, 2014 #1


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    I have a question that has been puzzling me for a while.

    When I drive my truck and accelerate hard until 25 mph then put the clutch in to roll freely, the truck will climb a few more mph before beginning to slow down. This is on flat ground or even a slight uphill.

    The way I see it is as follows. Say acceleration of the truck is 5 ft/s2 (random number). Once the clutch is in the force from the engine is now 0, and therefore acceleration should be 0 unless there is another force pushing the truck forward. However in order to be continuous, acceleration cannot jump from 5 to 0, and will have to decrease continuously. While it is decreasing it is still positive and will cause velocity to climb slowly.

    Can anyone explain the physics behind this?
  2. jcsd
  3. May 16, 2014 #2


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    Science Advisor

    I assume that you are watching the speedometer to determine whether you are speeding up or slowing down.

    In order to smooth out the readings so that the needle (or the digits) do not vary wildly, the number that is displayed will be some kind of decaying average of the most recent measured values.

    As long as your current speed is still higher than the currently displayed average, that average will still be going up.
  4. May 16, 2014 #3


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    So its is not continuing to accelerate. Thanks for the answer that has bothered me for a while now!
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