Various Laws in engineering etc

[Softus]

The question is this: When the particles have all gone and the closed system contains pure energy, do the apples still fall towards it?

The answer is this: No.

I don't think there is any proof that inertia and gravity really have the same origin, ie mass.

I think there is lots of proof.

It is assumed that they do because all our experiments point that way but that's not proof.

In that case you must have redefined the meaning of the word "proof".

 

[Space cat]

The answer is this: No.

I'm inclined to agree; massless photons should not have a gravitational field. But, if that is true, in what sense is mass conserved in a closed system?

I think there is lots of proof.

There is lots of supporting evidence but no absolute proof.

In that case you must have redefined the meaning of the word "proof".

Not me; Karl Popper:

"Every genuine test of a theory is an attempt to falsify it, or to refute it."

Or, to put it another way, there are no proofs, only counter-examples. Newton's second law stood the test of centuries of experiments but is now known to be not quite right and his definition of momentum, namely mass x velocity, is not conserved. Einstein gave us the correct formula for momentum - or did he? There's another theory waiting for a counter-example.

 

[tim west]

The counter "proof" for momentum is the M25

 

[2scoops0406]

the angle of the dangle is equal to the throb of the knob.

As long as the effort remains constant !

 

[tim west]

And the applied force is adequate.

 

[Space cat]

massless photons should not have a gravitational field

Now I'm not so sure. Photons may not have mass but they do have momentum and this changes as they pass a massive object. If we are not to violate the law of conservation of momentum, the mass that deflects the photons must be pulled towards them as they pass. If the force responsible for this is not gravity then what is it?

One of the problems with gravity is that it's really difficult to make useful measurements. We cannot generate large gravitational fields in the laboratory and, even if we could, their effects upon small particles would still be negligible. Although gravity is often quoted as being the weakest force in nature, I suspect it will be the toughest nut to crack.

 

[tim west]

The scientists of the world musn't underestimate the gravity of the situation.

 

[Space cat]

The scientists of the world musn't underestimate the gravity of the situation.

Nice one!

We are always being told that gravity is the weakest force in nature but rarely by people who are falling aff ladders! Time to go --

 

[Richardp]

try making a decent cup of coffee without it