# Momentum and Friction?

#1
Hi,

Friction decreases the velocity of objects right? So it would decrease the momenta of objects. In an inelastic collision, the kinetic energy of the system is lost to friction, yet conservation of momentum still applies. Why is that? Why do you lose kinetic energy to friction and not lose momentum?

Thanks.
0
7 years ago
#2
It's just a simplification. If there is friction, momentum after will be lower, but strictly speaking, it's conserved because the momentum of the earth and air particles will slightly increase. Total momentum in the universe is constant.
1
#3
But in calculations, we can see that the final kinetic energy of the system is not the same as the initial kinetic energy of the system. Yet we still apply the conservation of momentum?
0
7 years ago
#4
The Kinetic Energies are seen in Collisions and friction is usually negligible in them. If the initial and final K.E are same, the collision is elastic and if not, then inelastic.

The difference in K.E is not due to friction but due to the type of collision that happened.

P.S If someone can verify this please do. I hope I am right.
0
7 years ago
#5
Momentum and energy are both conserved in the collision.
In the case of energy there are different types. Kinetic, potential etc.
Kinetic energy is not conserved because this type of energy gets converted into another form in an inelastic collision. (Here maybe heat or sound or potential of deformation.)
The universal principle is conservation of energy. Energy and momentum are two quantities that happen to be conserved. In the case of momentum there is just momentum. No "other forms" for it to be converted into.

You may also like to consider the fact that momentum is a vector quantity while energy is not.
Apply this to the case of two cars which collide head on and both come to rest.
How does this affect the momentum and kinetic energy? Where has the energy gone? What about the momentum?
1
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