碰撞小记(Collision notes)-其他

碰撞小记(Collision notes)

2022.5.15

2022.5.15

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Collision notes

2022.5.15

2022.5.15

Without special instructions, the two objects colliding have the same weight

Part I

I never found out what great use kinetic energy can do. Until I learned elastic collision in my sophomore year of senior high school, I found that I had always misunderstood collision. I always thought that two objects collided. The object with high speed exerted force on the object with low speed, decelerated the object with high speed, accelerated the object with low speed, and then reached the same speed. After the common speed, it is relatively stationary and has no force, so it always maintains the common speed.

Part II

But this is not the case. It’s amazing that two iron balls collide, and the speed is directly exchanged!

It’s really mysterious. What’s going on? According to the physics book, momentum and kinetic energy should be conserved after collision, because they are not converted into internal energy. Then the two equations are combined to solve the velocity. It’s mysterious.

As a person without kinetic energy in the mechanical system, I certainly can’t say it like this. First of all, even if I admit the conservation of kinetic energy, well, just like momentum, the conservation of kinetic energy is a result, not a cause. We know that momentum is conserved in the end, but we can’t infer speed from it, and the logical order can’t be reversed.

So the object is coming. Why not co velocity, but exchange? Both satisfy the conservation of momentum, but why the latter? Why does the common speed still play a powerful role? Is my mechanical system wrong? Kinetic energy is actually of great use?

Due to various things, I can’t think about this problem until today. But it must be clear that my system is absolutely correct! Absolutely right!

Part III

Is this a misunderstanding? But that’s what they did when I discussed it with them
Think so. Perhaps the teacher is wrong, or the teaching materials are fooling around. Anyway, it is a common misunderstanding: elastic collision occurs on a rigid body, that is, there is no deformation in the process of elastic collision. Later, I found that the so-called elastic collision, as long as the deformation of the colliding object can be completely restored. In fact, this is probably the official definition.

Part IV

Get to the point. In fact, the conclusion is very simple. After all, the problem lies in the problem itself.

The so-called elastic collision occurs simultaneously.

First, there is a force between the two objects, and the speed tends to balance until the common speed.
Second, the resulting deformation gradually recovers, and the resulting force is the same as the previous force.

Therefore, common speed.

Write this first and write it well next time.