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Horizontal forces

  1. Dec 9, 2013 #1
    I have a surface that has minimal to no friction and I have used an elastic band to set my disc off from one end of the surface to the other. It crashes into the wall the other side and rebounds. How can I work out the acceleration. Am I right in assuming that at first the disc travels at a constant velocity because of minimal friction and then crashes into the wall and this is the first time it experiences acceleration in the form of deceleration to be brought to a halt. So am I able therefore to simply work out the distance travelled before it comes to a halt and the time taken?

    Many thanks in advance guys :D
     
  2. jcsd
  3. Dec 9, 2013 #2

    sophiecentaur

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    In an ideal situation like this, simple Newton rules and the velocity is constant. You will need more information to decide what happens during and after the collision.
     
  4. Dec 9, 2013 #3
    What sort of information would I need to determine how deceleration works to bring it to a halt?
     
  5. Dec 9, 2013 #4
    PS Am I able to simple assume constant velocity as the disc approaches the wall, ie distance of the surface/time taken to travel from one end to the other?
     
  6. Dec 10, 2013 #5

    sophiecentaur

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    Which bit of the experiment are you considering? You have not made it clear. Are the start and final conditions relevant to your question (apart from launch velocity and zero final velocity)?
    In the drift phase, there is no acceleration so time = distance / velocity. At the start, you would need to estimate the energy stored in the band and assumed that all goes to KE of the disc. The impact phase is anyone's guess until you specify something about the nature of the wall it hits.
     
  7. Dec 11, 2013 #6
    Thank you. Well I intend to work out initial velocity by working out how long it take to get from one wall to the other. However, after impact I know it will deceleration but by how much I'm not sure. The wall is a hard surface.
     
  8. Dec 11, 2013 #7

    sophiecentaur

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    ?? You still don't make it clear which order you are doing things. Have you measured something or are you trying to predict something? Some more background might be helpful (as ever) if you want useful responses. You can't tell what the acceleration was unless you know the distance or the time taken to get to speed. Even them, a rubber band has an odd force / extension characteristic (not like a Hooke's Law spring) so it would only be an estimate. If you actually want to find the launch speed then you could. perhaps, work that out by finding the force from the band over the range of stretched lengths and calculate the stored energy - and hence, the Kinetic Energy of the launched disc.
     
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