In physics, why do we have both energy and momentum of a moving object?

Question

Why is that a thrown baseball, for example, have "energy" and "momentum", both of which are conserved? What's the point of having both of them?

Originally, Newton only proposed a "quantity of motion", which is momentum. HIs works did not include kinetic energy. Kinetic energy was theorized by others, such as Galileo, Leibniz, Young, and it was even pointed out by Playfair that it may not be necessarily conserved!

If we have momentum, what's energy, then?

Please, don't just give me the formulas. I know already that p = mv, and E = 1/'2 mv² in classical mechanics.

Answer 1

Both are made up concepts that physists find useful when dealing with objects. One key reason why they are different is that momentum is _not_ always conserved--in an inelastic collision, for example. Additionally, they are useful for different reasons. Energy helps us understand the relatinoship between different types of energy--for example, how gravitational potential energy (being up high) translates equally (sans air resistance, etc.) into kinetic energy. Momentum helps us understand other thing, like collisions--for example, why, in space, it's much easier to move a very heavy object, but it will still hurt if that really heavy object hits you.

Answer 2

energy is stored in an object and changes from kinetic to potential energy and vesa versa , while the momentum is the rate of force to make the object move ( without fromula).

Answer 3

It takes energy to get an object to move and energy to get it to stop. While the object is in motion, it has energy that it is taking along with itself. To stop it you have to take its energy away from it unless the energy is taken away by something (somebody) else.