Simple 2D collision formula developments

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Discussion Overview

The discussion revolves around the development of formulas for predicting the new speeds and angles of two identical balls after an elastic collision in a two-dimensional space. Participants explore theoretical approaches and practical applications related to collision mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant, Adam, seeks assistance in deriving the new speeds and angles of two colliding balls based on their initial conditions.
  • Another participant suggests that a closed form expression exists and encourages searching through textbooks or online resources for the equations.
  • A different participant recommends transforming to the center of mass frame to simplify the analysis of the collision before converting back to the original frame to find the new velocities and angles.
  • Adam expresses difficulty in understanding momentum and requests a finished formula instead of a theoretical explanation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the specific formulas or methods to derive the new speeds and angles, and there are varying levels of understanding regarding the concepts of momentum and collision mechanics.

Contextual Notes

Some participants mention the need for algebraic manipulation to derive results, indicating that the discussion may involve unresolved mathematical steps and assumptions about the collision dynamics.

AdamAlon
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Hi everybody,
I am currently working on a small computer programming project, and was wondering if you could give me hand.

Say I have two simple, identical balls moving in different speeds and angles towards each other. They hit each other elastically, and weigh exactly the same.
The location of their centers is also a given (see diagram for further explanation).

http://img12.imageshack.us/img12/1108/question.png

All the data is according to the diagram (which is completely general).
Can I tell through some sort of formula developments what their new speeds (size+angle) will be, after they collide? (As in U1=?, U2=?, newA1=?, newA2=?)

I tried figuring it out myself but got mixed-up and lost. Hopefully you might be able to help me :-)

Thanks a lot,

Adam
 
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Oh sure. I actually had to do this myself for a computer game we made for a class project. I don't know the equations but you can get a simple closed form expression for it. I'm sure if you do enough searching on the web or through textbooks you will find out what it is. Of course in the end you could always derive it.
 
Born2bwire said:
Oh sure. I actually had to do this myself for a computer game we made for a class project. I don't know the equations but you can get a simple closed form expression for it. I'm sure if you do enough searching on the web or through textbooks you will find out what it is. Of course in the end you could always derive it.

Yeah, I figured it was rather simple, but I can't seem to find anything of that sort anywhere.
A closed form expression would be fantastic, but I am having a hard time deriving it myself. Thus, I turned to you guys for assistance :)
So, can any of you give me a hand?
 
Transform to the center of mass frame in which the total momentum is zero. Forget about the angles and velocities in the original frame for the moment. Just work out the most general case of a collision as seen in the center of mass frame (which is very simple).

Then transform this to a frame in which the initial velocities are arbitrary. You need to do a little algebra to find the angles in that other frame.
 
Count Iblis said:
Transform to the center of mass frame in which the total momentum is zero. Forget about the angles and velocities in the original frame for the moment. Just work out the most general case of a collision as seen in the center of mass frame (which is very simple).

Then transform this to a frame in which the initial velocities are arbitrary. You need to do a little algebra to find the angles in that other frame.

Sorry, I sort of lost you. I am yet to have studied momentum, and I tried to understand momentum from guides I have read.
Could you just give me a finished formula? I do not necessarily need to thoroughly understand the way...
 

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