How does a floor know you're standing there in order to produce a response force to exactly support your...

Question

weight? What is the mechanism?

My teacher posed this question to the classroom, and I can't find the answer. I read about forces, but don't know how the floor "knows." Any help?

Answer 1

It's a trick question.

The floor doesn't "know" anything. The floor simply responds in accordance with the laws of physics (in this case, Newton's Third Law, action and reaction in equal and opposite amounts; that's your "mechanism", by the way).

When studying physics, it is important to be as objective as possible, to recognize that matter and energy are governed by laws that, once you understand the underlying dynamics, are quantifiable and reproducible. It is important to steer clear of distractions such as divine or inanimate will, popular opinion, and anthropomorphisms. Saying "The floor knows how to respond" is anthropomorphic. Bad physics. The floor does not "will itself to respond to your weight", any more than your weight "wills the floor to bend". Saying "The floor supports your weight with an equal and opposite force" is focused, descriptive, and to the extent that your floor doesn't wear out over time, reproducible. Good physics.

Your teacher knows the difference. He or she asked the question that way to start you on the road to breaking bad habits about how to think about physics, and to start focusing on what really matters. Were all physics students so lucky as to have a teacher as insightful as yours, we would not be suffering from a science gap in the USA. Show your appreciation by paying attention in class and completing your homework assignments.

Good luck, work hard, and stay away from drugs.

Answer 2

The floor doesn't "know" in a cognitive sense. Your foot is deforming the floor. You're compressing a spring. You're trying to force positively charged nucleii closer to each other. The structure of the floor prevents it from moving much in response to your force. You are trying to push your protons into a repulsive electric field. The field is repelling your protons, but the field from your protons is also repelling the protons in the floor.

Answer 3

you could say that mathematically it has to happen in order for Newton's equations to work like they do, but that's kind of a cheap answer. also, you could say that when your hand pushes down on a table-top, the electromagnetic forces between the atoms of your hand and the atoms of the table top are opposing each other, which is the force you're feeling...if you use that one, you may get some bonus points :)