From post #2382 in the original thread -
Originally Posted by rwguinn View Post
Excuse me
I want to know more about the "Normal Force". What the heck are you talking about?
It cannot be significant, compared to g, since I have (a) never heard of it, and (b) never see a calcuation using it
I was using FF's term for the contact force between the building and the ground it was resting on. Because in the case under discussion the contact force is a normal force (as the building was vertical and the ground was horizontal) I didn't think the imprecision of terminology would do much harm.
How is this imprecise? Please explain how my example uses incorrect terminology. It doesn't. My example keeps things simple enough for anyone to understand, so they can see what is really happening. You are trying to take things to an unnecessary level in order to confuse the issue. There is no need for this.
I said that if a building rests on the surface of the earth it will exert a force on the earth. This force is from the gravitational pull of the earth, and the most common convention is to call this the force due to gravity. At the point of contact, the earth will exert an equal and opposite force on the building. This force is called the normal force, and this terminology is absolutely the most commonly used convention. If the building is not moving downwards or accelerating downwards, the force due to gravity and the normal force are equal and opposite to each other. Do I need to specifically state that the building is resting on a flat portion of the earth? If so, why are you trying to complicate things? There is nothing wrong with my statement. Nothing.
Edited after the entire text was posted - Oh, I get it, do I need to change my statement to the forces are equal in
magnitude and opposite to each other? Is that what you want me to do? If so, how does it make my original statement wrong? It doesn't. Just because you have a gravitational force and an electromagnetic force, my original statement is not wrong. You are nitpicking for no valid reason, and your nitpicking unnecessarily complicates things.
When the building is stationary with respect to the ground, the (upward) contact force of the ground upon the building balances the (downward) gravitational force of the earth upon the building.
We agree. The force due to gravity is equal and opposite to the normal force, based on a macro model and the most commonly used terminology.
But that does not make those two different forces
Why are you doing this? To keep things simple, we are looking at things on a macro level. That is all that is necessary to understand Newton's laws of motion.
Instead, you want to unnecessarily complicate things in a futile attempt to prove that I am wrong. This tactic, in the simplest terms possible, is lame.
You accuse me of being wrong because I don't take into account the microscopic nature of the forces involved. This does not make me wrong. It means I am trying to make the example easy to understand.
What you are doing is saying that the normal force, a contact force, is not gravitational. Your conclusion is that because the normal force is not gravitational, at a microscopic scale, the forces are therefore not equal and opposite. This is utter nonsense, and you are making things much more difficult than they need to be.
Watch this video.
https://www.khanacademy.org/science...ontact-force/v/normal-force-and-contact-force
The video clearly explains the force due to gravity and the normal force. He could have stopped there and been correct. Then, solely for the purpose of explaining things fully, he discusses things at a microscopic level and talks about electromagnetic forces, which are causing the atoms to repel each other.
His model is correct at the macro level. When he discusses things at a microscopic level, his macro model is still correct. He simply takes things to a level he doesn't need to.
How does unnecessarily taking things to a microscopic level prove I'm wrong? It doesn't.
How does your statement, "The contact forces are not gravitational forces, as they are electromagnetic in nature and act in the opposite direction to gravitation, holding the objects apart instead of drawing them together" prove I'm wrong?
Gravity is drawing the atoms towards each other. The electromagnetic repulsion of the electrons in the atoms is causing them to stay apart. I think you are assuming that these forces can not be equal and opposite because they are not the same type. If so,
this assumption is wrong.
Gravity is a force. Electromagnetism is a force. The magnitude of and direction of the forces due to gravity and due to electromagnetism can be equal and opposite to each other.
Watch this video -
https://www.youtube.com/watch?v=qt6MiLxeDv0
Once again, I have proven that I am not wrong. You have proven that you are unnecessarily trying to complicate things, and because I won't do this, you claim I am wrong. Why do you do this?
Everything I posted is correct. There are no statements that are wrong. Will you finally admit this?