Hey it's Professor Dave, let's learn about collisions. He knows a lot about the science stuff, Professor Dave explains. Whenever an object in motion comes into contact with another object, we can call this event a collision, and this concept applies to balls on a pool table just as it does to tiny molecules or huge celestial objects like asteroids and planets.
As we just learned, in any collision there must be a conservation of linear momentum. but this can manifest itself in different ways depending on the type of collision that is occurring, so let's go over these varieties now. First we will discuss elastic collisions. These resemble collisions between balls on a pool table where the objects involved remain separate after the collision occurs.
With elastic collisions, total kinetic energy will be conserved as well as the total momentum of the system, so the objects will bounce off of one another with no energy lost whatsoever as a result of the collision. We approximate collisions between atoms and molecules as being elastic when we refer to an ideal gas, just the way we do with billiard balls. There are many other examples of collisions that aren't completely elastic, but we can treat them that way like when a soccer player kicks a ball, since the player's foot and the ball do indeed remain completely separate after the collision.
We would refer to all of these scenarios as examples of nearly elastic collisions, since some kinetic energy is lost to heat and sound in each case. Perfectly inelastic collisions are those in which two separate objects collide, after which they move together as one mass. Sometimes when celestial bodies collide like two asteroids, the collision is inelastic and they fuse together to form a larger body.
In fact, This is how all planets begin to form, including the Earth, over the course of millions of such collisions. When we examine perfectly inelastic collisions, it is easy to analyze momentum, because we can treat the two objects as a single object after the collision, with a momentum equal to the sum of the two individual momenta. This is illustrated by the following expression, where m1 v1 plus m2 v2 equal to the sum of the masses times V final, which will depend on the magnitudes and directions of the two initial velocities. This approach can also be used to model car collisions, whether the two cars were moving in the same direction or opposite directions. Adding the masses of the cars and combining the velocity vectors will tell us what will happen after the collision.
We should note that during inelastic collisions like car crashes, total momentum is conserved. but total kinetic energy is not conserved. Much of the kinetic energy is converted into sound energy, which we hear as the sound of the crash, as well as heat energy and the internal energy of the new system, which allows the bodies to deform as a result of the collision.
That's why we call it an inelastic collision. An elastic band always returns to its original condition after being stretched, but with an inelastic collision, things are very different before and after the collision. The amount of kinetic energy lost during an inelastic collision will depend largely on what the objects are, and a variety of other factors. In reality, no collision is completely elastic or perfectly inelastic, but is somewhere in between, which we can simply label inelastic, implying that some kinetic energy is lost due to the collision, even if just a little bit.
So we can usually approximate a collision as being one of the two extremes. which will simplify the math that must be done in order to make predictions about systems that end up being extremely accurate. This concludes our study of linear motion, which from kinematics and dynamics to harmonic motion and momentum has been quite extensive.
But before we move on to circular motion, let's check comprehension. Thanks for watching, guys. Subscribe to my channel for more tutorials, support me on patreon so I can keep making content, and as always feel free to email me professordaveexplains at gmail.com