# Newtons's third law violation

1. Jul 8, 2009

### htg

Consider a toroidal solenoid powered by a sinusoidal voltage. This will lead to appearance of sourceless electric field, also sinusoidally varying with time. Now consider a conductive ball in the center of the system. Let the electric charge on the ball vary in phase with the voltage applied to the toroidal solenoid. Then there will be force acting on the ball, due to the E field, but no force acting on the solenoid - the net charge on the solenoid is zero, there are no sources of the field E produced by the solenoid. This violates Newton's third law (action and reaction).

Last edited by a moderator: Jul 8, 2009
2. Jul 8, 2009

### Staff: Mentor

Newton's third law is a statement of the conservation of momentum, and momentum is provably conserved in Maxwell's equations: http://farside.ph.utexas.edu/teaching/em/lectures/node91.html

The details of the scenario are irrelevant. If you get that momentum is not conserved then you have necessarily violated Maxwell's laws.

3. Jul 8, 2009

### htg

Just think about the presented example - it clearly shows that Newton's third law is violated (in agreement with Maxwell's equations).

4. Jul 8, 2009

### ZapperZ

Staff Emeritus
The "oscillating" charge on the ball creates its OWN changing E and B field which interact with the solenoid!

Zz.

5. Jul 8, 2009

### Staff: Mentor

Hi htg, ZapperZ just gave you the key, but really the details of your example are completely irrelevant momentum is always conserved regardless of the details.

Did you even read the link I posted? If so, what part did you not understand? I would be glad to help you learn the principles involved and understand the derivation.

6. Jul 8, 2009

### htg

The link you provided makes use of the idea that an EM wave carries momentum.
Even if we assume that it is true, we can see that the total momentum carried out by the EM wave is ZERO because of the symmetry of the system.

7. Jul 8, 2009

### ZapperZ

Staff Emeritus
This is getting sillier. EM waves carrying momentum isn't just an "idea", it is a FACT of experimental observation! The fault in your "thought experiment" has already been shown.

If you think that you have found a valid experiment that violates the 3rd law, then please publish it. Till then, this is unfounded speculation that violates the https://www.physicsforums.com/showthread.php?t=5374" that you had agreed to.

Zz.

Last edited by a moderator: Apr 24, 2017