Gravity -- Looking for knowledgeable answers.?

Question

Here's a series of related questions...

Do forces only translate energy through acceleration?
If so, how can we feel the contact force of the chair pressing against our bodies while sitting motionless on the Earth? Where does the energy required for us to feel the contact force go?
Where does it come from for that matter?
And if an object was never raised above any other object, would it be capable of falling due to gravity?
If two forces are directly balanced, is any energy moved through the system due to those two forces?

That last question should read: "If two forces are equally balanced", in case that makes a difference.

Answer 1

Yes, forces manifest themselves in the form of an acceleration. But to have motion, one needs a net force, to get a net acceleration relative to a referential.

You feel the force of the chair pushing bach because it is there to exert a force as a reaction to you sitting on it. Earth's gravity attracts each of your individual atom, but only the few atoms that are actually in contact with the chair are taking all of the resistance force, and let it radiate back though your body.

Take it another way: imagine you are falling in a vacuum (so there is not air resistance). You do accelerate downward, but you do not feel gravity, since you are in free fall.

Force is not energy. Energy is force with motion. If there is no motion, then the force is not creating or expanding energy.

So, the sensation of pressure of you sitting on a chair is just a force, not an energy transfer.

Answer 2

Acceleration is the only way to create kinetic energy from gravitation, but gravitational potential energy is always there, and it depends on:

U = mgh, where:

U is potential energy
m is mass of the object
g is the force of gravity
h is the height of the object above the center of gravity of the object attracting it (like the earth)

So no, gravitational forces also create potential energy as well as kinetic energy/acceleration, and that potential energy is always there.

As for the "contact force", this is caused by potential energy. While in a chair, you have the *potential* to fall if the chair suddenly vanished for some reason. The energy required for you to feel the "contact force" comes from gravity. Additionally, the chair must puch up w/ an equal and opposite force, as stated in Newton's 3rd law. Otherwise, you'd fall right through it.

If an object were "never raised...", it would only NOT be capable of falling if it were at the earth's core, at the center of gravity, where it had zero potential energy.

If two forces are equally balanced, we nerds say they are in "equilibrium." This could be stable or unstable, but in equilibrium NO energy is transferred.

I am a HUGE nerd and believe my answers to be correct, but I cannot guarantee their accuracy.

Answer 3

1. No, forces are translated through acceleration, energy is translated through different things, velocity being a main one, but velocity can occur even with 0 acceleration.

2. We feel it because of the normal force pushing up on us to allow us to sit on the chair and not break it or fall through it. No energy is required to push back up, just a mass and an acceleration, in this case it is the Earth and gravity pulling you and the chair is pushing you up with exactly the same force. The other two questions for this are now unanswerable.

3. Any object that is lifted is able to fall due to gravity, regardless of how high it is or what objects it is above. Like I said, Force ONLY depends on mass and acceleration, energy plays no part in it until you get to work and power.

4. No, energy is present, but it is not moved. At equilibrium energy is present, but stored. It does not move until something moves, then an energy will be present, that specific one being kinetic. Potential energy is rest energy, which you see here by balancing forces.

Answer 4

First statement true.

The contact force (or normal force) is felt due to the pacinian corpuscle which sends long-term stimuli about static pressures to the brain. There is no force, but merely a static compression of the pacinian corpuscles in the skin which forces the nervous system to send signals to the brain. Your teacher is confused about this, clearly. S/he does not know enough to teach physics properly.

The energy required to feel the contact force comes ultimately from the food energy we ingest. This makes ATP which powers the nervous system, and allows static changes in the pacinian corpuscle to send information about static forces.

If an object was never raised above another object, it would be capable of falling due to gravity so long as the object is above the surface of the earth.

If two forces are balanced, there is no energy moving through the system (provided that there is no breakage or deformation of either object).

My own comment:

Your teacher is an idiot.

Answer 5

I think you are mixing up two concepts. Mass exerts a force through accleration. Energy is a concept whose dimensional units are Forcexdistance, such as a newton-meter. Thus, energy need not be "translated" through accleration. What you may be thinking of is impulse, another entity of units force-time, which occurs due to loss of momentum (mass-velocity).

As for the chair, there is no energy involved unless the chair is removed. Then you plop on the floor. The chair counterbalances your massx accleration, so that when the massxvelocity by virtue of gravity when the hit the floor is not converted to impulse when you come to a halt.

Answer 6

Gravity is created by gravitons. Gravitons exist on all matter however they have very low amounts of energy and can be only felt when with very massive objects (e.g. Earth).
Gravitons are also the weakest energy particle which explains why you can attract a piece of nail upwards to a magnet and as if that the nail is not affected by gravity; but is affected by gravity.