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Question about physics

Discussion in 'Off Topic [BG]' started by Bardolph, Nov 5, 2004.

  1. Bardolph


    Jul 28, 2002
    Grand Rapids, MI
    So let's say you're standing on a linoleum floor and you have a basketball and a golf ball. You drop the golf ball from a height of 6 feet and because of the conservation of momentum, it bounces back up a distance X. You do the same with the basketball and it bounces back up a distance of Y. So then you make the assumption that if you drop the two balls together with the golf ball sitting on top of the basketball, the two momentums will add together and the golf ball will bounce back a distance of X + Y. But in actuality, the distance bounced is far greater. Why does this happen?
  2. Mike N

    Mike N Missing the old TB Supporting Member

    Jan 28, 2001
    Spencerport, New York
    When you drop the two together the golf ball will bounce off the basketball, which is moving, and that would help to project it further than if it bounced off the floor, which is stationary.
  3. Bardolph


    Jul 28, 2002
    Grand Rapids, MI
    We already know it's going to be a larger bounce. The distance wrongfully predicted is that the sum of the two individual bounces will equal the distance of the "team bounce," but it exceeds even that.
  4. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    I don't feel like figuring out the math, but the conservation of momentum says that mass times velocity will be the same before and after the impact. After the impact, the balls will decelerate at a rate determined by gravity. Deceleration is not linear, therefore the distance travelled is not a linear function of the starting velocity.

    I'll leave the detailed calculations to someone else. At the age of 40, I don't feel like doing your homework for you.
  5. Petebass


    Dec 22, 2002
    QLD Australia
    Because the basket ball acts like a trampoline.
  6. The basket ball acts as a cusion and therefore absorbs the force.
  7. As Pete said, the ball acts as a trampoline, and there is also a transference of energy to the golf ball from the bounce of the basketball. Hence, the basketball most likely won't go quite as high as it should. Instead, some of that energy will be transfered to the lighter golf ball, sending it higher.

  8. Selta


    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
  9. Eskimo, of course adding the heights issn't the way to do it.

    The way to do it is to add the forces. The basketball has a much higher mass, and therefore a much higher force than the golfball. It's mass times acceleration you need to be concerned about, not height.
  10. You're delving into elasticity, which is VERY hard to calculate.

    Given that the golf ball is lighter, and is landing not upon a hard surface but on a moving elastic surface, not oly does it not hit that surface as hard (because the surface itself is moving away from the golf ball) but it gets a little shove when the basket ball returns to it's nominal shape and rebounds from the floor. So your equation should not be X+Y, but X+Yx3/4Z (or something like that, where Z is the amoun of energy released from the elastic reshaping of the basketball.)

    I could be very wrong. If you want to go weirder, though, put the golf ball on the bottom.:D

    Rock on
  11. Now combine Davidoc's comment about force and the other comments about the basketball acting as a trampoline and you have the right answer.
  12. Oh, and you can also add air resistance into this one, which makes it even more of a mess. But let's just assume that we're not including that either.
  13. What is that supposed to mean? If you really want a perfect answer, shall I go and get my dad who is a physics teacher? :p
  14. P+M*V

    So momentum is equal to mass times velocity.

    The Basketball has much more mass than the golf ball.

    Then there's the Conservation of Momentum, Very involved equation dealing with vector changes, Pressure changes, mass, area blah blah blah.

    So just like in that clicking ball game ,5 balls on strings set the 1st ball in motion and and only the last ball gets pushed away, Thats due to the conservation of momentum. If the first ball had the mass of a basketball and the others a golf ball, you would see that once set in motion the energy would be more than sufficient to push off the last ball, all the balls and the basketball would continue.

    So the basketball has more mass than the golf ball and ergo greater potential enegy, when the balls "transfer energy" afer being droped and then rebounded. the greater mass of the basket ball propels the golf ball "with less mass" to a faster velocity. But momentum is conservered!!! P=M*V
  15. Selta


    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    Read the other explanations as to how the system works with elasticity, and you'll see how totally wrong you were, and I knew this, being a 4th year Physics student, an Engineering Physics and an Aerospace Engineering major at Embry-Riddle. Your dad may be a physics professor, but that does not make you one.

  16. dave_clark69

    dave_clark69 Guest

    Jan 17, 2003
    The basketball has a greater mass. Weighs more. Falls to the floor quicker, so it is bouncing back up while the golf ball is falling down. The golf ball will have a +ve momentum, and the basketball will have a -ve momentum. When they collide, the momentums are exchanged. example:
    Golf ball: 1kg 1m/s = 1Kgm/s
    Basketball 3kg 3m/s = 9Kgm/s

    Then think of it as the objects travelling towards each other.
    the golf ball will accelerate. The actual result will be greater because the basketball will absorb energy and bounce the ball back even further

    But, that is only the theoretical idea. You should have stated if it was an elastic collision.

    If not, tough, the maths behind it will be too hard
  17. Uhoh!!!! :meh: :rollno:
  18. Selta


    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    wrong wrong wrong. The balls will hit at the same time.

  19. dave_clark69

    dave_clark69 Guest

    Jan 17, 2003
    What do you mean uhoh?
    Are you using galileo's theory?
  20. +1 They fall to the floor at the same speed, if I do believe.

    EDIT: You guys beat me to it. :crying: