Energy conservation in collisions

In summary, the difference between elastic and perfectly inelastic collisions lies in the conservation of kinetic energy. In elastic collisions, the two objects involved are perfectly rigid and do not generate any sound, heat, or other forms of energy, thus conserving kinetic energy. On the other hand, in perfectly inelastic collisions, the two objects deform upon impact and dissipate energy in the form of sound, heat, and friction, resulting in the non-conservation of kinetic energy. This concept is often simplified for introductory levels, but it should be noted that perfectly elastic collisions only occur between atoms and molecules.
  • #1
member 392791
I was curious, why is energy conserved in elastic collision but not in perfectly inelastic collision? It said this in my textbook without giving any reason why.
 
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  • #2
Umm, isn't this the DEFINITION of elastic and inelastic collisions?

If you want a physical intuition beyond that, we think of elastic collisions as those where the two balls colliding are perfectly rigid. So when they hit each other, they just immediately start moving in a different direction, their accelerations being instantaneous. In an inelastic collision, as the balls hit they deform each other before moving off in different directions. This deformation leads to the generation of sound, heat, and frictional forces between the two, all of which dissipate energy. Being perfectly rigid, the hard-sphere collision does not suffer from this.
 
  • #3
'Energy' is always conserved, it is 'Kinetic energy' that is not conserved in inelastic collisions because of the generation of heat, sound and permanent deformation.
 
  • #4
ok well elastic collisions generate sound too...I didn't realize this was the definition, the book didn't make it seem like those were the definitions, they just stated that one conserves kinetic energy and the other doesn't, while both conserve momentum, without explaining it, leaving me confused.
 
  • #5
You are correct to say that momentum is conserved in all collisions. Kinetic energy is only conserved in perfectly elastic collisions. If any other kind of energy is generated then it is not perfectly elastic.
If sound is produced the collision is not perfectly elastic.
I think it is fair to say that perfectly elastic collisions only occur between atoms and molecules.
 
  • #6
Oh ok, so it's that a ''perfectly elastic'' collision has no sound, heat, or anything else. I think this is a simplification made for intro level, because we are having perfectly elastic collisions applying to more than atoms. I was thinking elastic, didn't realize there was perfectly elastic. It said elastic and perfectly inelastic without mention of perfectly elastic, but I think they mean to say perfectly elastic.
 

Related to Energy conservation in collisions

What is energy conservation in collisions?

Energy conservation in collisions refers to the principle that energy cannot be created or destroyed, but can only be transferred or transformed. In a collision, the total amount of energy before and after the collision remains constant.

Why is energy conservation important in collisions?

Energy conservation is important in collisions because it helps us understand and predict the outcome of a collision. Without energy conservation, we would not be able to accurately determine the speed, direction, and other properties of objects involved in a collision.

What types of collisions conserve energy?

All types of collisions, whether they are elastic or inelastic, conserve energy. In an elastic collision, the objects bounce off each other without any loss of energy, while in an inelastic collision, some of the energy is converted into other forms such as heat or sound. However, the total amount of energy before and after the collision remains the same.

How is kinetic energy conserved in collisions?

In a collision, kinetic energy is conserved because the total amount of energy before and after the collision remains the same. This means that the sum of the kinetic energies of the objects involved in the collision is equal before and after the collision.

What factors can affect energy conservation in collisions?

The main factor that can affect energy conservation in collisions is external forces, such as friction or air resistance. These forces can cause a loss of kinetic energy during a collision, making it not fully conserved. Other factors, such as the elasticity of the objects and the type of collision, can also play a role in the conservation of energy in collisions.

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