# Can someone explain the action-reaction in physics to me?

If I push on a refrigerator, it pushes back on me. This is in Newton's third law. Every action has an equal and opposite reaction.

However, refrigerators aren't living. So how can they push back on me? Like, "I'm a refrigerator. A human is pushing on me. I'll push back on them." That doesn't happen, right?

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• does it move when you try to push it?

Do you feel a lot of resistance in your hand when you try to push it?

THAT is the refrigerator "pushing back" against your hand

If it didnt then it would move and your hand would not feel any resistance

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• in structural engineering beams are loaded with weight , what hold up the beam is called reactions and there are two reaction to hold the weights on top of the beam. Thus the reactions balance the beam. Hence to have stability  in a system it must be in equilibrium.

To every energy there is an equal and opposite reactive energy.

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• Anonymous
9 months ago

You don't need to be alive to exert a force.

Imagine 2 negative charges. They repel, it's called electrostatic repulsion. Each exerts a force on the other. The 2 forces are (badly named) the action and the reaction.

The electrons in the atoms on the surface of your hand and the electrons in the atoms on the surface of the fridge repel.

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• Another way to think about it is when you push on the refrigerator, it doesn't move. Nevertheless you ARE pushing on it meaning the net force Fnet = 0. That means there must be an equal and opposite force canceling the applied force.

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• This is the least well understood principle of all Newton's works.

Action and reaction only applies to two forces AT A POINT.

Your idea of a "push" is to do with ENERGY. But Newton's laws are to do with FORCE.

A very different thing.

Now at some point you attempt to provide a force on one side of that point.

But the mass of a point is zero. ( a point is an infinitesmally small portion of space.).

So it would instantly accelerate out of the way of your hand.

UNLESS there is something in the way.

So as the atoms that you start pushing move away they get closer to other atoms that are stationary.

This gives rise to electrostatic forces that exactly equal the force you are applying until the other parts can move out of the way.

Now consider other ways of viewing the situation.

You hit a solid lump of rock. Hard. Does it hurt? Yes. Why? because the rock resisted moving.

Now TRY to apply a force to the air in front of your hand. You can't. Why? Because the air just gets out of the way.

And as every action has an equal and opposite reaction you cannot apply a force BECAUSE the air cannot give a reaction force.

The rock CAN AND DOES give a reaction force. So you can apply a force to the rock and the rock can apply a reaction ( and break your hand as it does so. )

No force can be made unless something is able to oppose that force.

Every action always has an equal and opposite reaction force AT THAT POINT.

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• Anonymous
9 months ago

action reaction

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• Yes, I can explain it. No the refrigerator is not a living thing. That's totally irrelevant. You have two forces AND inertia, Newton's first law of motion. Thou are pushing the refrigerator and the equal but opposite force is PRESSURE. The refrigerator is not going to move, because it is at rest and has mass and the force of gravity acting on that mass, until the force of your push is greater than the pressure and friction of the refrigerator.

Forces are vectors. They have DIRECTIONS as well as magnitude. You have 3 forces forces here, the force of your push, the pressure, and the acceleration of gravity at right angles to the other 2 forces.

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• It has nothing to do with living or non living. When no force is applied momentum remains a constant. mv= constant.

Here m= your mass+mass of the fridge. Assume only two are involved. Assume at t =0, v=0. Then constant is 0. Suppose you push tht fridge with a velocity v. You give the fridge this moment. the fridge will move with negative velocity or move in the opposite direction or push you back with the same momentum. This is the action and reaction principle. the push is internally generated.

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• We start with the sum of all forces acting on that immobile refrigerator is zero. In math talk that SUM(f) = 0. How do we know it's zero? Because it isn't accelerating and from F = ma we know that if a = 0, then F = SUM(f) must also be 0.

OK then, if you're pushing against that fridge door with a push P and the sum of forces at that point on the door is zero then P + F = 0 must be true.

Which means that F = - P or, ta da, the reaction force F must be equal to but opposite direction of the push. (The minus sign is the opposite direction indicator.) So by direct substitution we have P + F = P + (-P) = P - P = 0 QED.

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• You might have a breakthrough reading quantum phyzicz (excuze the z`..zorreeee:)

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