momentum and mass

[forufes]

this thing has been driving me crazy for some time and i can't figure it out..

 

is a projectile with a bigger mass better for absorbing as much momentum from a potential energy source (mechanical spring or chemical blast) or a lighter one?

[J.C.MacSwell]

this thing has been driving me crazy for some time and i can't figure it out..

 

is a projectile with a bigger mass better for absorbing as much momentum from a potential energy source (mechanical spring or chemical blast) or a lighter one?

 

All other things being equal twice the mass can absorb twice the momentum (or for that matter twice the energy) in the same way.

 

Normally a "projectile" would have it's momentum absorbed, rather than the other way around, but the principle still holds.

[forufes]

by projectile i meant launched thingie, didn't stress the "passing momentum" part yet:D..

 

the best example to give is a gun, either fiing real bullets "powered" by black powder, or a toy gun powered by a spring.

 

which will reach further and have a greater impact (meaning absorb more energy)? the one with mass X or 2X?

 

i THINK the heavier one will have more momentum, but less kinetic energy, = more impact, less range.

 

and vice versa..

 

but whether what i said is right or not, i still can't grasp the concept..i can't visualize it.

 

also, consider the potential energy source is SO big it can be considered infinity, like a nuclear bomb, does this extreme change anything? does the relation between them change here?

[timo]

I think that might depend on the constraints. I am not sure how to tackle your examples - I did not fully understand them. But imagine a pipe with some black powder in the middle and two bullets of equal mass on either side of the explosive. When the explosive explodes, there is some energy 2E released that (due to equal mass) spreads evenly over the two bullets - note that the energy E each bullet gets is independent of the mass of the bullets. Both bullets have opposite momentum of equal magnitude (so that the total of zero remains conserved). Since momentum and energy are related by [math] p = \sqrt{ 2mE} [/math] ( <- very simple rearrangement of classical physics formulas) you see that for the same explosion, i.e. the same energy released, using heavier bullets leads to the bullets having more momentum.

That is not really the scenario you sketched but hopefully a start for you to a) show you that you can actually calculate the answer to such questions and b) show how it's roughly done. For say real guns you could make one of the masses significantly larger (that mass being the rifle) and still assume a constant energy released (that seems to make sense to me). The energy does not spread equally over bullet and rifle but of course conservation of energy (Erifle + Ebullet = Eexplosion) and momentum (pBullet = -pRifle) still hold and should be sufficient to get pBullet as a function of the bullet's mass.

[JPGreco]

Well, it depends. Momentum is Mass * Velocity. A object with larger mass has the potential to have achieve greater momentum since it doesn't have to be traveling as fast as an object with less mass. However, an object with less mass has the potential to aquire more momentum depending on its velocity.

 

You're question about an energy source providing the velocity is also a little skewed. Since an energy source needs to do more work to impart its energy into the object, two identical energy sources acting on two objects of different mass will impart different amounts of energy into those objects. The object with the smaller mass will gain more energy, since less is used to overcome its inertia, and will achieve a higher velocity than the object with the larger mass.

So according to your question, a larger object is actually less accepting to energy to used as momentum since more energy is used to overcome inertia and other friction forces.

I guess the potential for maximum momentum is in favor of an object with more mass because as velocity would approach the speed of light, the momentum of the object would be greater of an object with less mass approaching the speed of light. So yes, larger objects have more potential in the grand scheme of things, but really, the potential of an object is based on parameters outside of its mass, namely the force being applied.