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Why there is no force acting in an object with constant velocity?

  1. Jun 21, 2013 #1
    According to my level of knowledge,my point of view regarding an object moving with constant velocity is that there should be a force acting on it for its continuous motion(eg:when riding bicycle we give a force continuously).But the theory says it is not.can anyone explain???
  2. jcsd
  3. Jun 21, 2013 #2
    On a bicycle, if you stop pedaling, you don't immediately stop. You keep moving with the same velocity you had just before you stopped pedaling, and then you gradually slow down. Slowing down is due to forces acting on your bicycle--wind resistance, friction in the wheels, etc. But if there were no force acting on your bicycle to slow you down, you would continue to coast at a constant velocity once you stop pedaling. But since there are forces acting to slow you down such as wind resistance, maintaining a constant speed requires you to pedal just enough to cancel the resistance force--when one force cancels the other, you are left with zero net force and thus remain at a constant velocity.
  4. Jun 21, 2013 #3


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    But there are forces acting on a material point moving with constant velocity. It's just that their resultant is 0. The second postulate of mechanics only speaks about the resultant force, not on individual components.
  5. Jun 22, 2013 #4
    So the bicycle doesn't move due the force given by me.But the force I gave only cancel out the air resistant and frictonal force.I am I right?
  6. Jun 23, 2013 #5


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    That's correct. Velocity is not related to currently acting forces. Only acceleration is related to currently acting forces. constant velocity = no acceleration = sum of forces is zero.
  7. Jun 23, 2013 #6


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    Obviously I need more clarity to understand that one

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