So, from what I understand, Newton’s third law says that for every action, there is an equal and opposite reaction.
I’m having a very hard time wrapping my head around it, as it seems as though if his law worked the way I interprete it to, pushing an object or denting an object would be impossible.
For example,
If someone were to push a book on a table, the force they applied on the book to push it, should be countered by an equal and opposite reaction force, therefore not allowing them to move the book.
In another example, if someone were to push a piece of metal, there should be an equal and opposite reaction force (normal contact force?) which would not allow the person to move the metal (can’t dent it), no matter how much force they use.
I guess what I would like to know would be why this is not the case in the two above examples, and what is it that I am not interpreting correctly with Newton’s third law.
Thank you!!
In: Physics
When you push a book with your hand, you feel pressure on your hand. That pressure is the equal and opposite force in Newton’s third law. The force deforms your hand a little but otherwise doesn’t do anything noticeable, because it’s not a very strong force. The force you apply to the book moves the book because the book is light and has little friction with the table. The force of the book pushing on you does very little because you are much heavier than it and you have plenty of friction between your feet and the ground. But, importantly: if there was no equal and opposite force at all, then you wouldn’t feel anything while pushing the book (no pressure against your hand).
If you push against something heavier, you may notice that you have to brace yourself. Maybe you have to lean in a little or position your feet so you have more grip on the ground. Now the opposite force is more noticeable. If you do this on a slippery surface (e.g a well-polished floor) the opposing force may be enough to push you back a little.
If you push against something in space, the opposite force is totally obvious. If you pushed against a book in space, the book would go flying in one direction quite fast, and you would drift off in the opposite direction much more slowly. If you push against something that’s the same weight (or *mass*, to be more precise) as you, then you both go flying off in opposite directions at the same speed.
So in short: yes, the opposite force is always there as Newton said. If there is a force from A to B, then there is the same force from B to A. But what these forces do to A and B depends on their properties (mostly their mass). The same force acting on a light thing may cause it to shoot away at speed, while it doesn’t even budge a heavy thing, because it’s not enough to overcome the friction between the heavy thing and the surface it sits on.
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