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Normal force in space

by shreder
Tags: force, normal, space
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Travis_King
#19
Mar27-14, 01:04 PM
P: 841
If we are assuming that there are zero gravitational affects on the ball and table besides their own gravitational attraction (either they're reaaaallly deep into space, or they're in free fall / orbit), if you were to place the ball on the table and they then both remain at rest, there will be no measurable "normal force". However, if you were to place your right hand on the ball, and your left hand beneath it, under the table, and squeeze, you'll create a normal force.

She's right, the normal force is not restricted to gravitational situations, it's just that that's what tends to happen hear on earth in basic situations.

Think of brake pads on a rotor. When the pedal is depressed and the pads squeeze, there is little to no force produced by gravity, it's all hydraulic pressure causing the forces, yet there will be a normal force on the surface of the rotor.
Travis_King
#20
Mar27-14, 01:09 PM
P: 841
Quote Quote by sophiecentaur View Post
She is correct about the fact that there will be electric forces between the molecules in contact between ball and table. These forces will be much greater than the gravitational ones.
In the vacuum of space, these forces can cause substances to weld together so they are difficult to separate. The effect was a surprise for early Space Engineers.
Though...the electric forces wouldn't act on the CoM of the ball, so there wouldn't be a "normal force", no? Perhaps momentarily as the two objects fused together.

OP, as far as this is concerned though, I imagine we're assuming that the table and the ball are both non-metallic or that they were brought up to space from our atmosphere, where they've already got a nice protective oxidation layer.
craigi
#21
Mar27-14, 01:14 PM
P: 421
Quote Quote by shreder View Post
all i wanted to know was if without weight there still would be a normal force
this all started because my physics teacher that has only a degree in chemistry thinks she is smart "the normal force has nothing to do with gravity"
well thank you all for posting your answers
Although you are correct that in the absence of other forces, setting the gravitational force to zero results in no normal force, that does not prove that the normal force is a result of gravity. The normal force is just a force perpendicular to the surface of contact that prevents interpenetration. The action of gravity is only one of many ways that contact can occur, so your teacher is completely correct.

Keep up the skepticism, but don't be so quick to give your teacher a hard time either. You don't need a degree is physics to understand this level of mechanics.
dipole
#22
Mar27-14, 01:27 PM
P: 440
If people really want to be nit-picky, the true origin of the "normal force" is due to Van der Waals forces and electron degenceracy pressure. Both of which are far beyond the scope of the OP and most people who would have questions about this, so I think the thread is pretty moot at this point.


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