# The Naked Scientists Forum

### Author Topic: From a physics perspective, what happens when two objects collide?  (Read 4048 times)

#### LetoII

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##### From a physics perspective, what happens when two objects collide?
« on: 02/06/2012 19:55:37 »
If 2 objects collide 1 moving at a relatively low speed and the other at a freaking high speed how does this affect the results on impact?

I heard you can use a banana to shoot through wooden sheds if you fire it with sufficiently high speed for example, and that would be under the condition where you'd have air resistance. Is there a limit to this except for maybe light speed?
« Last Edit: 14/06/2012 08:27:31 by chris »

#### RD

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##### Re: effect of highspeed on impacts
« Reply #1 on: 02/06/2012 20:35:29 »
... i heard you can use a banana to shoot through wooden sheds

or a chicken ... https://en.wikipedia.org/wiki/Chicken_gun

#### graham.d

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##### Re: effect of highspeed on impacts
« Reply #2 on: 02/06/2012 23:05:24 »
When two objects collide the effect on the objects is related to their elasticity. If both objects are perfectly elastic then no energy is dissipated in either object and they behave like perfect billiard balls. In practice objects are not perfectly elastic, or not even very elastic at all and so the kinetic energy of the objects is dissipated in the objects themselves. Generally the structurally weaker object comes off worst! However, this does not mean the seemingly strong object does not get damaged. As RD alludes to, dead chikens are fired into jet engines to test the capacity of the engine to withstand a bird-strike. Jet engines can be badly damaged if not strong enough to survive this but the chicken definitely comes off worse:-) The same would be true of a banana and a wooden shed, though I have never seen this demonstrated.

#### LetoII

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##### Re: effect of highspeed on impacts
« Reply #3 on: 03/06/2012 03:09:05 »
thanks, that chicken comparison makes things pretty clear :D
Does the LHC also test collisions by smashing particles into eachother at different speeds? If not, could it show different results if we did try it?

#### syhprum

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##### Re: effect of highspeed on impacts
« Reply #4 on: 03/06/2012 23:24:52 »
I believe at the LHC they perform experiments colliding heavy nuclei such as lead or gold with protons which would have similar energies but different speeds

#### LetoII

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##### Re: effect of highspeed on impacts
« Reply #5 on: 10/06/2012 00:42:32 »
i just thought of something that bugs me abit.
If in the LHC 2 particles are made to collide with eachother moving very much near the speed of light, can one say this impact of the 2 objects happens at almost double the speed of light?

#### Geezer

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##### Re: effect of highspeed on impacts
« Reply #6 on: 10/06/2012 01:24:29 »

dead chickens are fired into jet engines to test the capacity of the engine to withstand a bird-strike

The Snopes "Catapoultry" topic is worth a read.

http://www.snopes.com/science/cannon.asp
« Last Edit: 10/06/2012 01:26:04 by Geezer »

#### LetoII

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##### Re: effect of highspeed on impacts
« Reply #7 on: 10/06/2012 14:26:23 »
I guess it was a strong kitty

#### evan_au

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##### Re: effect of highspeed on impacts
« Reply #8 on: 10/06/2012 23:31:10 »
Energy is very important: E=1/2mv2. This means:
• If you double the mass of a projectile, the energy it carries goes up by a factor of 2.
• If you double the speed of a projectile, the energy it carries goes up by a factor of 4. 10x speed means 100x energy (and so on...).
It is energy that does much of the damage in a collision (and take materials beyond their elastic limit).

Momentum is also important: P=mv
This means that the fragments from the collision will generally continue in the direction of the object with the greater momentum.

The speed of light is a firm upper limit (as far as we know). Two objects traveling at 90% of the speed of light in opposite directions do not collide at 1.8 times the speed of light, but somewhere around 99.4% of the speed of light. This is a consequence of the special theory of relativity. http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_theory_of_relativity

#### The Naked Scientists Forum

##### Re: effect of highspeed on impacts
« Reply #8 on: 10/06/2012 23:31:10 »