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Collisions

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Numsgil:

--- Quote ---it worx coz momentum cant be converted to any energy form. its kenetic energy that can. if I throw something in space at one direction, my body gets movementum in the other direction, which would be - compared to the thing I throw. if it have 5 as momentum, then I get 5 momentum in the other direction. so it becomes like 5-5=0. still 0 momentum. no matter what you do, it will always be 0
and PY, ure 42, right?, you should know better than thinking momentum and kenetic energy are the same, its completly different thing
--- End quote ---
Uh, Zelos, I think you're a little confused.

Momentum is mass times velocity.  In your example, you're assuming you started with 0 velocity, so when you throw the end system still has 0 momentum.

But if you throw something when you're already going 3 m/s then the end momentum and the beginning momentum aren't 0.

I don't think PY was saying that momentum and KE are the same thing.  Just that sometimes KE (and thus momentum) are converted into heat, light, explosions, etc. in some collisions.

That is, not all collisions conserve KE perfectly.

Botsareus:
I did not say I want no energy loss during movment. Friction etc. is all good ideas, thats why I voted for choise 4

Botsareus:
But if the new legues will use this new , slow , collisions ,then I have no choise , I will use them too.

Numsgil:
What do you mean by 'slow' collisions.  Mostly what happens now is that bots won't bounce off each other.  They'll either kind of stick together or do this:

O>.....0   -> O0 -> O.... 0>

Where > denotes motion.

PurpleYouko:

--- Quote ---and PY, ure 42, right?, you should know better than thinking momentum and kenetic energy are the same, its completly different thing
--- End quote ---

Where did I say they were the same thing?

Momentum is Mass times velocity
Kinetic Energy is 1/2 MV squared

Whoopdy bloody do!

What I said was

--- Quote ---(For simplicity's sake momentum and kinetic energy are assumed to be the same)
--- End quote ---
That just means that is a shit load easier to discuss and explain things in terms of conservation of momentum that it is to bring KE into the conversation.

And NO! Momentum most certainly does not alway equal zero!
Try throwing a ball at a wall covered in soft plaster.

Try this calculation for size!

Before collision
Ball velocity = 20
Ball mass = 10
Ball Momentum = MV = 200

Wall mass = about 20,000
Wall velocity = 0
Wall momentum = 0

Collision!!!!!!!!!
!!!!!!SPLAT!!!!!!!
Ball sticks in soggy plaster

Ball velocity now zero
Ball momentum now zero
Wall velocity OOH Look It's still ZERO
Wall momentum is STILL ZERO

Where did your momentum go?

Well neither the wall or the ball are moving any more so IT ISN'T THERE ANY MORE

Why?

Because the kinetic energy of the ball was absorbed by the plaster and used up completely in reshaping it from a nice flat surface into a big sodding dent!

KE and momentum may not use the same calculation but they are very similar in nature. Both can be imparted or absorbed by other features in any system and DO NOT ALWAYS EQUAL ZERO. In fact the only time when momentum in a system can actually be zero is when that entire system has reached maximum entropy.

That is just basic physics.

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