How can Newtons third law be disproven?

Question

third law- Every action has an equal and opposite reaction

Answer 1

They don't call it a Law for nothing you know.
Wherever you look, you will always see an action-reaction paired up. Newton's 3rd Law fits nicely in with another law which we know holds true in all cases...the Law of conservation of momentum.

Answer 2

This is easy.
Rig up a device which causes an action. Lets say the device is someone sitting on a really good skateboard who will throw a bowling ball along the axis of the wheels. Measure how fast the bowling ball travels, and measure how fast the person travels in the opposite direction.

You could instead put a wedge shaped track on the skateboard that will guide the ball from the front of the board to the back if you carefully put the ball straight down on the top of the track. The track must line up with the wheels, and the wheels must turn easily for this to be valid. Carefully measure the velocity of the bowling ball once it leaves the skateboard. Measure the velocity of the skateboard contraption also. multiply each mass by the respective velocity. Newton's law says that the mass times velocity of each will be equal.

Now comes the fun part. Show that there is no explanation for the discrepancy. Once you have eliminated all sources of error from your experiement, the difference is how wrong Newton was.

Answer 3

The speed of light trick is interesting. I have a feeling that it would be hard to test though ; )

Newton's laws have been shown to actually be very good approximations of fundamental laws of physics for those times when things are larger than atoms, but smaller than super-massive stars. Newton's law of gravity was refined significantly by Eistien's thoery of general relativity.

The third law is an immensely useful approximation of the macrospoic effects of the electromagnetic force. In fact, the forces aren't "exactly oppostite and equal", a tiny ammount of energy is always lost to heat in any collision. The total ammount of energy is unchanged, but the sum of the resultant momentum's need not be equal to those before the collision.

So Newton's third law is actually disproven as a hard and fast rule by the laws of thermodynamics. That dosn't mean that it isn't useful for analysis, though.

Edit - Mj, you mean Hiesenburg's uncertainty principal. Pauli is famous for his exclusion principal.

Also edit - on further review, the speed of light solution isn't going to disprove newton's third law. If you hit something that's moving at near the speed of light with another object (which will have to be a massless particle, like a photon), that object will indeed impart a force on the fast-moving -thing-, but the force simply will not accelerate the thing to an appreciable degree.

Answer 4

Newton's third law is on very solid ground when you are talking about forces between objects that are touching so that the action and reaction forces are applied at the same point in space. But the third law can get into trouble when you are talking about action at a distance forces.

David Griffiths shows how the third law is violated in section 8.2 of his Introduction to Electrodynamics book. He shows that two electric charges approaching each other, one moving vertically down and the other moving to the left, exert magnetic forces on each other that are NOT in opposite directions. Therefore Newton's third law is violated.

Answer 5

The only way you can disprove the third law of Newton is when you travel at the speed of light. At this speed no matter how much action you put in, no reaction can be observed. According to Einstein all three Laws of Newton cannot apply and can be proven wrong when you travel with the speed of light.

Answer 6

By having an action that doesn't have a reaction, or one measurably less than it should be. That would be a sign that Newton's third law needs correction.

Not that anyone has found such a thing to happen as of yet.

Answer 7

1- physics laws can be broken. if not , why we think now that earth is moving around the sun. before it was the sun moving around the earth..

2- gravity has nothing to do with it. gravity or not still applies. if not then how the rockets and space shuttle move in the outer space.

3- all newton laws is classical physic that means . it doesn't apply when we talk about "speed of light" or "Atomic" that's modern physics. its already proved that it doesn't work perfectly under that environment

Answer 8

The snide, cynical part of me says: "Figure out some way to factor it into evolution, and you'll hear hundreds of ways."

Another part of me says "Go watch a hollywood movie where a guy gets thrown back 50 feet after being shot by a bullet. Yeah, there's good physics."

That said, unless there's a radical redefinition of physics, I don't see how that theory's going to be disproven any time soon.

Answer 9

there is no way to disprove. cause it is proven that it is right. but as a matter of fact when you travell at the speed of light all three laws can be disproven. more over those laws just don't work.

Answer 10

Physics Laws are universal truths. They cannot be disproven. It applies even to Aliens.