Is conservation of energy a myth?

Question

Consider three particles (say of mass 1Kg) such that to one of them the other two are travelling at 90ms-1 and 100 ms-1 in the same direction and the one travelling at 100ms-1 slows down to 90ms-1.

To an observer on the first particle the change in Kinetic Energy is 1/2 * 100^2 - 1/2 * 90^2 = 950J

To the observer on the particle travelling at 90ms-1 the change in Kinetic Energy is 1/2 * 10^2 - 1/2 * 0^2 = 50J

Obviously the change in energy could be used to, say heat water - so why would one observer see 19 times as much water heated as the other? This is not a specific relativity problem - the speeds are too low!

Anonymous · Accepted Answer

I have no idea what you're talking about I think.

Maybe this'll help:
With energy and stuff. There's no thing as perspective. It loses or gains one certain amount, no matter from where you look at it.

Bullet Magnet · Answer

There is a far greater difference between the energy of the stationary object and the second moving object than between the two moving objects. That extra energy you have observed is still in the form of kinetic energy, not heat.

Pointy · Answer

The kinetic energies of these 3 particles are independent of each other. They are moving independently of each other and so the kinetic energy (or change in kinetic energy) of one particle has no bearing whatsoever on what is happening to the other two.

Keith T · Answer

You are comparing things from two different reference frames.  The Kinetic energy of an object is directly dependant on what you define zero velocity to be.  

figure out what your exact reference frame is, then express each objects velocity in terms of the basis vectors of that reference frame, then calculate the changes in kinetic energy.  I assure you it works.

Energy can neither be created nor destroyed.  It can only change form.

As for heating water. remember that Temperature is a measure of the average kinetic energy of the particles of the object or fluid WITH RESPECT TO the reference frame of the center of mass of the object or fluid.  something striking it and conferring energy to it as thermal energy would have to have its kinetic energy expressed in terms of the reference frame of the object of fluid.  

I would study up on tranformation matrices.

ALAN B · Answer

Keith T:  Think on this. Energy cannot be destroyed, only change form, e.g. gas to heat, coal to gas to heat etc. On the theological theme, what happens to the body's energy when the living body dies? The body runs on electrical currents; when the body dies, does the energy stick around ( maybe why some folk can see apparitions) or does it dissipate ( the soul). This is a serious question and comment, and has been a puzzle to me for ever!!

zi_xin · Answer

Your method of calculating KE is derived from Netwonian Mechanic which only deals with non-moving reference frames.  The usage is correct in the first case but incorrect in the second.  That is reason for the difference.

Anonymous · Answer

yes, for every energy saving theory there is one to knock it down, but never mind it is another way for us to be taxed so be happy

ahnolds · Answer

Yes

Is conservation of energy a myth?

8 Answers