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Acceleration of an object - Help needed

  1. Oct 16, 2006 #1
    Hi, please help me settle a bet...

    When a pitcher throws a ball, can the ball accelerate after it leaves the pitchers hand? Same question with a bullet and a gun...

    I say that once the force of either the pitcher or the explosion of the gas in the gun stops, the ball or bullet won't accelerate any more but will start slowing down as drag and gravity start taking affect...

    Is that line of thought correct?
    Can someone please give me the science behind the answer?

    I am a physics amature with alot of discovery and science channel knowledge but no formal physics education and any help to prove an answer would be appreciated. Thanks
     
  2. jcsd
  3. Oct 16, 2006 #2
    Let's take the bullet as the example.

    1) The bullet will accelerate towards the centre of the earth due to gravity.
    2) The bullet will deccelerate due to air resistance, this is effectively the same thing as acceleration.
    3) The bullet will accelerate due to the Coriolis effect (unless the bullet is fired along the equator).

    In short, YES, the bullet will accelerate.
     
  4. Oct 16, 2006 #3
    But will the bullet accelerate towards the target in perspective to the shooter in an example of a shooting range? I mean, will it go faster towards the target once it leaves the gun?
     
  5. Oct 16, 2006 #4

    Doc Al

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    No. Your thinking is correct. (The myth is that the bullet keeps gaining speed for a while after it leaves the gun. Nope. Same for the tossed ball.)
     
  6. Oct 16, 2006 #5
    Can you please explain why? When I told him my thoughts, he said that he just "knows" that the object accelerates after the initial force stops. I agreed that with a gun, the expansion of gasses might still push the bullet a bit after it leaves the barrel, and his thought was that the bullet accelerates for a few hundred feet. Any scientific explanation would be appreciated. Thanks
     
  7. Oct 16, 2006 #6

    Doc Al

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    Acceleration requires a force. Ask your friend what provides the force. (Does he really think the gases still push the bullet after hundreds of feet? :rolleyes:) For the thrown ball, obviously the hand exerts a contact force against the ball--lose that contact, the force is gone.
     
  8. Oct 16, 2006 #7
    There actually is some additional acceleration a thrown ball experiences after leaving the pitcher's hand...it's known as the Magnus force and is due to the ball's spin. However, it cannot add any forward velocity to the ball, it can only exert a force tangential to the oncoming air.
     
  9. Oct 17, 2006 #8
    Does anyone have any science to back this theory up?
     
  10. Oct 17, 2006 #9

    ZapperZ

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    Er.. it's called Newton's 2nd Law! F=ma! If there's no force, there's no acceleration. It is that simple.

    Any intro physics text will have that.

    Zz.
     
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