/sci/ - Science & Math

is it to do with electrostatic attraction? They are stronger than gravity, so no net downward force. Doesn't need to be a constant outpouring of energy to keep it there.

>>2637910
Why would it have anything to do with electrostatics?

The man with the barbells is stronger than gravity too, but eventually he gets tired, because gravity is still exerting a force on his weights.

Gravity must be still exerting a force on the mass of the magnets, no?

>>2637926
>implying magnetism gets tired

>>2637943

Damn you, just because it doesn't get "tired" doesn't mean that it isn't defying the force of gravity.

Does a planet orbiting the sun need to be fed energy to keep orbiting? No. Matter bends space-time like a pool ball on a tarp.

In a similar way, magnetic and electric forces distort space around them.

>>2637951

gravity itself is a force that doesn't deplete, unlike muscles

>>2637926
hammer a nail into the side of a tree.

is the nail exerting energy because it is going against gravity? no.

same thing with the magnet. it becomes one with the metal like the nail with the tree.

>>2637951
You are still expending energy to hold the dumbbells up. You are pumping blood to your arms and your muscles are being constantly contracted to keep your arms stiff.

>>2637951
Is it so strange?
You have no trouble accepting gravity to be a constant force. Where does gravity come from? How come gravity defys the force of the man lifting weights?

It's odd you find the idea of gravity being a constant force perfectly natural, but then find it odd for magnetic force to behave in a similar manner

>>2637962

First of all, that's EXACTLY my point.

>>2637954

Bullshit.

>>2637959

That's not true.

>However, I assume that some energy must be expended to hold it there against gravity, just as in the case of the man holding up the barbells.

You assume wrong. This is only true for your muscles. Magnets don't get tired any more than tables or chairs do.

Muscles work differently. Your arm would use energy even if I was to move it back and forth for you.

Maybe the energy is expended as the magnets slowly get weaker over time? Eventually the magnet will drop because the attractive force won't be strong enough anymore?

>>2637962
you expend energy because you body is constantly moving, no matter how hard you try to keep still.

>>2637959

LOL

the nail is exerting force against the tree, that's what keeps it fixed in place

>>2637975
Whats your problem then? Forces are not a human body... You said it yourself there is no work done if there is no movement. There is movement in a human body, thus it is doing work. A magnet on a fridge is not moving thus it is not doing work.

>>2637996
it doesn't *create* the force, moron, because it has no source of energy and isn't moving.

your arms create the force when you hold them still because it has a moving source of energy (blood).

>>2637988
So if you were able to hold something perfectly still--say, to keep a rubber band stretched--your muscles would never get tired? I imagine (though I don't know) that to maintain tension in muscles expends energy regardless, because without that energy they would go slack.

>>2638014

It's your muscles fibers that are moving you twat

>>2637959
The nail becomes the part of the structure of the tree.

For instance if there's a trailer of chickens with a roof on top and they all flap upwards at the same time, the trailer still has the same mass. But then if the roof was taken off and the chickens flapped up all at once (presumably back down into the trailer) the trailer has a lesser mass when the chickens are outside of the 'structure'. But if the chickens are within the structure as they flap then the trailer is just as heavy. Just like the nail and the tree.

It's one of those crazy physics things

>>2637988
wrap your head around this:

someone tapes a small weight in your hand, then tapes you hand to the wall above your head. do your muscles get tired? no, or not as tired if you were to fight gravity by holding the weight without assistance.

>>2638021
yes, we are in agreement.

>>2638026
Why do the fibers have to move to remain perfectly still you tweet?

>>2638040

ask a physical therapist. Thats how muscles work. In order to apply a force, your muscles have to keep moving.

>>2638021
no, thats not true at all. Your mixing models and reality up. It doesn't become part of the tree, you model it as part of the tree.

>>2638037
I wanted to tell that little anecdote D: to support you even further, and it's rather memorable

You're over thinking it. The basic laws of motion state that an objects motion is based on the sum of the forces acting on it. In the case of the weight, your arm must continually exert force to counter act the force of gravity on the weight. Your muscles can only exert a force for so long before they wear out, thus the weight drops.

But, for the magnet on the fridge, there is a physical property of the magnet that causes it to stick to the metal. This sticking causes there to be friction between the magnet and the surface of the metal. In order to move the magnet, you must apply enough force to counteract this friction. The force of gravity doesn't change, so if it's not strong enough to move the magnet at the start, it never will be...

>>2638051
you got the idea, didn't you?

>>2638068
I got the idea yes, but I just had to point out how it's wrong. Because you could very easily model the nail not as part of the tree. You could very easily model the truck with chickens as the truck with chickens in regardless of the roof.

The way it was said made it appear like thats what actually happens in reality, when it really isn't. The forces are still acting on all the objects, we just simplify the model because we can. In the case of the nail because the forces on it are balanced, and in the case of the truck, because we don't where the mass is coming from.

if you havent taken a physics class dont fucking answer physics related questions. some of this shit is depressing to read. nail in a tree? magnet becoming one with the fridge? holy fuck.

No, no energy is expended to hold the magnet against gravity. You don't understand the concept of force fields and their associative vector fields. Don't be a cocky faggot and think otherwise. The force of the magnetic interaction between the magnet and the fridge is much greater than gravity, through a free body diagram and vector addition it should be obvious as to why the magnet remains against the fridges surface. If you have no idea what I'm talking about then just shut the fuck up and sift my response for the generic answer.

>>2638095
Hey tiger, if the side of the fridge were perfectly frictionless, would the magnet stay up? I don't think so (assuming the material of the fridge is identical along the path to the floor). So don't bullshit.

>>2638184
Although, the magnet will adhere even to the underside of a ferric surface, so maybe I was the one who was BSing.

>>2638184

No, it wouldn't stay up since the magnetism is only pulling it sideways, perpendicular to the pull of gravity. That really has little to do with OP's question, because when you lift a weight you are opposing gravity. The magnet example was made under the assumption that there would be friction to hold it up.

>>2638095
But why? That's what we're all discussing -_- and you've just came in an blabbed shit after you hadn't read any comments. Afterall i'm an A2 physics student >:( and i'm interested to know too

>>2638291

What do you mean but why? Did you read his post? He was pretty clear.