My book (Halliday, 6th ed: Section 20-4), uses the momentum of the individual molecules in a gas to derive the pressure of the gas. They imagine the molecules hitting a wall. I'm a little rusty on my memory of conservation of momentum, so this equation is confusing me a bit:(adsbygoogle = window.adsbygoogle || []).push({});

(delta)p_{x}= (-mv_{x}) - (mv_{x}) = -2mv_{x}

They then say that the molecule delivers +2mv_{x}of momentum to the wall.

Are they approximating the wall as much more massive than the molecule, so the molecule's speed is unchanged (velocity opposite)? So to get from +mv_{x}to -mv_{x}you would take

mv_{x}-mv_{x}-mv_{x}= -mv_{x}

to get the change in momentum?

I'm thinking I'm probably right, but I just feel a little queezy about it. Like there is something I'm not getting. I guess what I don't understand is the sentence: "the momentum (delta)p_{x}delivered to the wall by the molecule during the collision is +2mv_{x}."

Could someone possibly start from scratch and show how all this comes from the conservation of momentum?

I hope I made sense.

Thanks a lot.

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# Homework Help: Momentum and the pressure of an ideal gas. Easy Question.

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