# Tag Info

18

Let's talk about what the normal force is. First of all, it is a feature of solids, which is to say materials that resist penetration by other materials. When two solids are in contact they resist interpenetration; they resist occupying the same space. Now, if something (be it gravity, your own hands, or simple motion) brings two solids toward one another ...

14

The normal reaction force is not necessarily equal to weight. When you jump, you push down on the ground. That pushing force plus your weight result in a normal reaction force larger than your weight, which is why you are propelled off the ground. For astronauts in a space ship, they can push against a wall to generate the normal force necessary for ...

6

Newton's third law: when two bodies interact, they apply equal but opposite forces on one another. Whenever you go to apply this, you have to be really careful that you're consistent about which two bodies you're talking about. The weight is the force that the Earth as a whole applies to the box. It has nothing to do with the ramp. By Newton's 3rd law, the ...

4

Friction exists in space, just that not in the most familiar cases. Walking or rolling are not normally possible without gravity pushing both bodies in contact with a normal force. However the normal force does not have to be only gravity, it could be caused by pressure or some other force (thrusters, magnetism etc). Fluid flowing through a pipe in space ...

3

Friction occurs only when a body starts or tries to start its motion in contact with another body. In space if two seperate bodies can stay in contact then friction must occur there. Here nothing to do with gravity.

3

This isn't surprising. Remember, $\oint$ means that you're integrating around a closed path. Without that requirement you can't use Stokes's Theorem to get a curl. All you've shown is that a constant vector does no work if you go in a big loop. This is the situation with, for instance, gravity close to Earth's surface. You throw a ball in the air, and when ...

3

It's perfectly possible, because it's not just any work; it's the work done around a closed curve. If you have a uniform force field (which is a special case of a conservative force field) and you move an object around in a closed curve you won't get any net work out of the force field. A good example is gravity close to the Earth's surface.

3

Physics is not mathematics. It is an observational discipline that uses mathematical formulations to fit observations and predict the behavior of new set ups. Experimental observations can be fitted very accurately by defining four fundamental forces and the way elementary particles interact under these forces, weak, electromagnetic, strong and ...

2

What I have done is to add the $569\;\mathrm{N}$ vector with $μ_kn$ and finding the horizontal component of that resultant vector. Something's wrong here. The resultant force vector should not have any other components than the horizontal one - otherwise the object should be moving vertically also, which it doesn't. In the sentence here it seems that ...

2

If your ramp has friction holding the block in place, then you could talk about the total force the ramp applies to the block, and this total force would point directly opposite the force of gravity, and it would have the same magnitude, giving a net force of 0. It might be more useful to consider the case where there is no friction whatsoever. In that case, ...

2

"Normal" is a mathematical synonym for "perpendicular" addendum after comment Yes, I read the question too fast. The normal force is caused by very small compressions of the intermolecular bonds connecting the first layer of molecules to the second. If those bonds are perpendicular to the surface, it's clear that the force will be perpendicular. ...

1

At first approximation, the mass cancels out. This is because the force to accellerate a object to a specific speed is inversely proportional to mass, but the friction force is proportional to weight, which in steady gravity is proportional to mass.

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When calculating the gravitational field of extended objects we typically break them up into infinitesimal masses then integrate to sum up the effect of all these masses. As it happens this process is described for a disk in the answers to the question The potential and the intensity of the gravitational field in the axis of a circular plate. The advantage ...

1

Yes there is friction in space. Friction and gravity are two different concepts. On earth mostly we experience friction because we are always in contact with earth surface due to gravity and whenever anything is in contact with other surface frictional force will come into picture(static of dynamic friction). I have done some quick research for you who ...

1

You are correct that you need three equations for three unknowns. In addition to the total thrust equaling the vehicle weight, you need to establish horizontal axes at right angles to each other and calculate the net moment of the three thrusters about each axis. The net moment about each axis must equal the moment of the vehicle weight about those axes. So ...

1

Mass is a constant that relates how momentum and energy are balanced. In prerelativistic physics, energy is $mc^2+p^2/2m$ and in relativistic physics energy satisfies $E=\sqrt{(cp)^2+(mc^2)^2}$ and the former is approximately equal to the latter when $|pc|<<mc^2.$

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The relation is empirically observed across a wide range of materials and conditions. But it is not exact. Attempting to derive a similar equation just from lower-level physics such as solid surface molecular interactions would be horribly complex.

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Check out the solution in the image. It will be dependent on the inclination of the plane. Here, a is the horizontal acceleration of the inclined plane.

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If people are not exactly synchronous, the first person that wants to release the stick loses contact and thus can't. The problem is that people are not pushing (with just extra pressure if not succeeding in moving), but must "pull without attachment". So just by gravity it would keep balanced on all contact points only for no more that 2 people for a stick, ...

1

Any basic course in statistical mechanics can potentially cover Fermi-Dirac and Bose-Einstein statistics; see for example this introductory course that Google brought up, which begins defining things at a relatively low-level. If you are at an advanced level and have already had a basic course in statistical mechanics but want to quickly brush up and tackle ...

1

You also need the total thrust to balance the weight of the ship. That is your third equation. You have guaranteed that the ship does not rotate, but it could accelerate vertically (either up or down).

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From your geometry, I would solve it this way. Based on symmetry, your front thruster has no roll authority. So in hover, the left rear and right rear must be equal. (1) Use the lever arm front and rear of the front thruster by itself and the rear thruster pair to eliminate any pitch moments. (2) Total thrust to match weight. (3) Since they're all ...

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