It very simply states that there is an EQUAL and OPPOSITE reaction for every action, If I Punch a Wall and the Wall Punches me back, The reaction of my punch. If the wall punches me back with the same force does that mean that is has lost some energy? But in the process of me hitting that wall, I have also punched the air molecules with the same force, so how could there ever be motion? shouldn't the air molecules punch me back with the same force? Please don't tell me that they have really less mass therefore their force would be negligible, The Law clearly states that the Forces are always equal no matter the mass. If I hit my couch and then hit the wall why does it not hurt the same? I get that the couch absorbs the blow but the force I applied was the same, why is it that all motion exists if the direction of the reaction is opposite and it is equal hence the resultant force would always be zero due to the '-' sign of the reaction. It would be very kind of you to explain to me the answer if you have the knowledge, kindly keep in mind that I won't understand the strong Calculus that some of you may use to explain to me. Thank you!
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3Does this answer your question? Given Newton's third law, why are things capable of moving? – PM 2Ring Jan 01 '24 at 06:48
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1"if the direction of the reaction is opposite and it is equal hence the resultant force would always be zero due to the '-' sign of the reaction" - these two forces affect different objects and therefore don't add up. There is no resultant. – Filip Milovanović Jan 01 '24 at 12:45
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1Things don't work the way you think they do. When you throw a ball at a wall, you initially exert a force on the ball, but as the ball flies, the only forces on it are gravity and the forces exerted by the air molecules, and their resultant points down and backwards at all times - yet the ball is moving forwards nevertheless. There is no forward-propelling force on it. The force you threw the ball with is not "carried" by the ball. Similarly, if your muscles stop acting at any moment prior to contact, your fist will be carried forward by inertia and there will be no forward force on it. – Filip Milovanović Jan 01 '24 at 12:46
2 Answers
You don't punch the air molecules with the same force as you punch the wall. Think of a bulldozer and a party balloon. The bulldozer can push with a force of ten tons, say, but if it comes in contact with the balloon, the balloon moves out of its way at the slightest touch, so the bulldozer does not get to apply the ten tons of force to the balloon.
You need to consider what happens in slow motion and at a microscopic level. When you move your fist through the air, molecules in the air make contact with the outermost molecules of your skin, and they interact with tiny forces that are enough to cause the air molecules to move out of the way. It is only when you hit the wall that the molecules in the outer layer of your skin experience a bigger force that causes your skin and hand to compress, and it is only when that compression has built up and transmitted itself through your body to a sufficient extent that the full force of your punch can be applied. During the process of punching the wall, you and the wall both distort to some extent. At the very first contact, the distortion is small and the restoring force is small too- it is only as the distortion builds that the forces involved build. It happens very rapidly in the case of the wall, which brings your fist to a halt very quickly. When you hit your couch, the process of compressing the material in the couch takes much longer, so your punch is decelerated at a much slower rate, which is why it doesn't hurt to the same extent.
Remember that energy and momentum are conserved, so if you want to make a ball move by kicking it, you have to give up some of your momentum and energy to the ball. The amount of momentum the ball gets is the same as the amount you lose. The ball speeds up by getting the momentum from your leg, and your leg slows down. The ball speeds up as a result of a force applied by your kick, and your leg slows down as a result of the equal and opposite reaction from kicking the ball.
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Sir, I loved the explanation and you are by far the best "Teacher" I have learnt something from, but are you implying that during the process of punching the wall, there is a vacuum between my hand and the wall? Well it is true that if a bulldozer hits a bunch of balloons that are in the way of it hitting a wall, some of them will still remain the the but majority will fly out, similarly the air molecules due to less mass get accelerated to a high extent, there should be a pressure difference between me and the wall during the few seconds of the punch right? @Marco Ocram – gsdvgsdfgsf Jan 01 '24 at 12:49
how could there ever be motion?
This is by far the biggest misconception with this law. Simply put, in completely empty space if you push a box, the box feels a force and thus accelerates.
By Newton’s 3rd Law, you too feel a force which is equal to the force you exerted but in the opposite direction. That is it, that is the only force you feel. Thus, you too accelerate. The accelerations will be inversely proportional to the masses.
This is a statement of conservation of momentum.
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Sir, you cannot "That's It" a doubt. You have to explain why "That's It". – gsdvgsdfgsf Jan 01 '24 at 12:42
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That’s it as in that is the only force you would feel. That is what the law says. The explanation (derivation if one can call it that) is also included, it’s conservation of momentum, any textbook will do a better job reproducing why conservation of momentum leads to this law and also why we think conservation of momentum is a feature of the universe. I recommend you read the linked posts at the top from here on. Best of luck! – JohnA. Jan 01 '24 at 14:31