# Newtons first law: implications on kinetic energy

## Main Question or Discussion Point

Newton's THIRD law: implications on kinetic energy

kmarinas86 said:
For every force, F, there is an equal and opposite force, -F. If the inertia of one object is greater than that of another object, the inertia of the greater object will do work on the smaller object, pushing it a distance, d.

Fd-Fd=0

If I jump forwards (due to the electromagnetic structure of the molecules of my body), the binding energy of my constituent molecules is increased, while I produce radiation as well as kinetic energy directed at the floor. Therefore, all other things equal, I add an impluse to the earth equal to the integral of (Force * time). Some of the kinetic energy impacts onto the earth becomes radiation. But the radiation has a (momentum*speed of light) which we can interpret as a radiative energy, as an analog to kinetic energy (since they are transformable to each other). The change in pressure*volume would therefore correspond to my change in kinetic energy+the change in my radiation + the change in the earth's kinetic energy + the change in earth's radiation... Would it not?

Would then change in pressure*volume correspond to 2*Fd, or while disregarding radiative loss, twice of the change in my kinetic energy, thus, mv^2?
edit: after thinking about it a little more, I realized something. After having landed, my kinetic energy becomes what it began as (practically zero). nvm then.

Last edited:

Related Classical Physics News on Phys.org
Andrew Mason
Homework Helper
I lost you when you started talking about pressure*volume. Are you talking about the atmosphere? How does kinetic energy and radiation affect PV?

Also, are you suggesting that the kinetic energy of the earth is equal to the kinetic energy of the person jumping?

AM

Last edited:
Title is wrong - I should have said Newton's THIRD Law

I lost you when you started talking about pressure*volume. Are you talking about the atmosphere? How does kinetic energy and radiation affect PV?
No, not the atmosphere.

Well, these may have common cause. In an engine, when fuel is burned, the molecules of the fuel increase in temperature. This affect the kinetic energy of the particles and also results in radiation. The change in pressure*volume is reflected by this (see P-V diagram).

Also, are you suggesting that the kinetic energy of the earth is equal to the kinetic energy of the person jumping?
Actually, now that I think about it, this isn't correct.

The forces on both objects may be the same at a given moment in time. But the displacement is different for each object if each object has a different mass. Therefore the change in kinetic energy will be inversely related to the mass of the particle of the two considered. If something weighs 100 more, the change in its kinetic energy over the course of the change forces will be 100 times less (due to having a equal but opposite force on it at all times but over 1% the distance... also: $\Delta x = .5at^2$).

Anyways....

Last edited: