Conservation of momentum

Discussion in 'Physics & Math' started by Adam, May 22, 2002.

  1. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    Can people please give me some clear examples of what conservation of momentum entails? I think the phrase is fairly descriptive, and I believe I have a good idea of what it's all about, but I'd like some people who have studied physics more extensively to describe it for me please.
     
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  3. Joeman Eviiiiiiiil Clown Registered Senior Member

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    momentum = mass x velocity.

    It is like doing free body diagram except replace force with momentum.

    Hope that helps.
     
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  5. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    What is a free body diagram?

    See, I dropped out of high school early to join the military, completed year 12 after that with no maths or science, and am only now getting into maths/science education.
     
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  7. thed IT Gopher Registered Senior Member

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    Adam

    What it basically means is that the total momentum, mass times velocity, is the same before and after a collision.

    If you have two masses m and m' with velocities v and v' their combined momentum is,

    p=mv+m'v'

    Let us say they hit each other so that they stick together. The new combined mass is m+m' but what is the new velocity v<sub>1</sub>, we have,

    p=mv+m'v'

    and after the collision

    p<sub>1</sub>=(m+m')v<sub>1</sub>

    From conservation of momentum

    (m+m')v<sub>1</sub> = mv+m'v'

    Hence

    v<sub>1</sub> = (mv+m'v') / (m+m')

    That is ignoring various things like elasticity which only adds a complicating factor or two.

    More practical offshoots of this, which you intuitively understand, would be car collision. Imagine two identical makes of cars, travelling in parallel at the same velocity. If they drive into each others sides, there is some damage but not much. Now have them drive at each other, the damage is considerable. What matters here is velovity. In the first case the velocities almost cancel. In the second, they add and the momentum goes way up.

    Another example is a collision with a 32 ton truck and a car. No matter what, the truck wins. He has the larger mass and larger momentum. Due to conservation of momentum the relatively small amount of velocty the truck looses transfers to a large momentum gain to you. End result, your car falls apart.

    Same for a warship Vs. sailing boat or Warship Vs. Lighthouse on a rock.

    Imagine also what happens if you tried to catch a canonball. It's momentum is so large that you gain lots of momentum and get thrown backwards, a lot.

    All examples of conservation of momentum.
     
  8. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    Good good. I figured it might be that simple, but wanted to make sure. Everything is balance, equilibrium, yin and yang... Good grief, soon I'll start talking like FoxMulder...
     
  9. thed IT Gopher Registered Senior Member

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    More like Truthseeker, momentum is not demonic.

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