Why do things fall?

Question

Is there like some force or something? could you build a machine to stop it happening? then you could float and stuff, like the aliens :-)

Well my question was a little bit tongue-in- cheek. I mean it was kind of pretending that there is an easy answer. And of course there isn't.

Answer 1

Gravity slows time. So as an object enters a region of lower time, it loses potential energy. It must increase kinetic energy to maintain a balance of energies. This explains why things accelerate when they fall.

What I do not yet understand is why something falls when you first release it. If it is in motion in any direction, then it will be directed down (towards the center of gravity of the greater mass). But when you first release an object, if there was no motion to send it off in some direction, it ought to simply float. I am not satisfied with this yet--although every time I have released something (not filled with helium), no matter how carefully, it does always fall.

Gravity bends space, which may be the same thing as slowing time. If there were some way of increasing "temporal friction," to keep objects from sliding down space/time gravity wells, that might work.

I have not seen your floating aliens. But I hope I may have given you an idea for an antigravity machine. I want to ride your prototype when you have most of the bugs worked out.

Answer 2

Newton's gravitational law specifies there is a force F between any two masses m and M that is = GmM/R^2 G is a constant of proportionality that is supposedly the same for all masses and R is the center to center distance between the two masses.

The direction of that force vector (F) is along the line that connects the centers of the two masses. Thus, for us on surface Earth, the force is pulling us with mass m towards the center of Earth with mass M.

That force vector is always on us and anything else that has mass. So, even when we are standing up straight, F is trying to pull us into the center of the Earth.

Because F comes from gravity, we have a special name for it...we call it weight. So, that's why things fall...they have weight. And they have weight because gravity tugs at their respective masses.

Now we know not everything falls to the Earth. Satellites orbiting around our planet do not fall and crash into the surface for example. Why is that?

Well, turns out their net weight is zero; so they do not fall. Net weight is w = W - F; where W is the weight of the satillite due to gravity and F is a force that offsets W so that w = 0 and the satellite stays up there in orbit. That force F is called centrifugal force. You may know centrifugal force as that tug you feel when going over the top on a roller coaster for example.

The same type of thing happens with satellites, but instead of going over the top on a roller coaster, they speed around the Earth in an orbit. And just like in the roller coaster, going around in circles like the satellite does creates that F, that centrifugal force. And, again, when W - F = w = 0 the net weight is zero and the satellite stays up there in orbit.

So, yes, we can build a machine that stops things from falling...satellites are examples of such machines. But we can't get rid of the force of gravity. It's always there where there is mass. So we create a counterforce, like centrifugal force, to balance out the weight of a mass; so that the net weight is zero.

There are other counterforces we can use. Magnetic forces have been used successfully to counteract the force of gravity for instance. Perhaps you've seen the floating ball novelty item in Brookstone or the Discovery stores. The balls are held up by magnetism so they don't fall. There are also experimental trains that ride in the air because they are held aloft by magnetic rails that counter the force of gravity on the trains.

Of course, the most popular counter force of all is simply some physical thing to keep you from falling. For example, you don't fall into the center of the Earth, where gravity is trying to pull you, simply because the surface of the Earth prevents it. It prevents it because it pushes back against your weight with a counter force F. As consequence, the net weight w = 0 = W - F.

You probably find these answers uninteresting. I suspect you were looking for some sort of antigravity answer. That is still scifi stuff. Although antigravitons have been theorectically described, they've never been detected. And for that matter, gravitons, the theorectical messenger quanta that some theories propose have never been detected either. So a machine you can turn off and on like a light bulb to make it float or fall is still science fiction, with the emphasis on fiction.

Answer 3

Surely you already know that things fall down because of gravity. But, are you also aware that things fall up because of gravity?

It's true. According to Newton’s third law every force has an equal and opposite force. So, if the earth exerts an unbalanced force, called gravity on the object in your hand, then that object also exerts an equal unbalanced force on the earth.

The object that you drop accelerates to the earth because unbalanced forces, in this case, gravity, always cause accelerated motion. That equal and opposite force that the object exerts on the earth causes the earth to accelerate upwards towards the object.

I know that this sounds really stupid! No one has ever seen the earth accelerate upwards towards an object that they have dropped. But, according to Newton’s third law, this must happen.

We do not see this because the acceleration of the earth upwards is, of course, very, very, very, very small! So small that it is on the order of 0.000,000,000,000,000,000,000,000,1m/s^2. So, while it is not a measurable quantity, it is a quantity that can be calculated. (F = ma, so a =F/m. The mass I used is one kilogram; the mass of the earth is on the order of 10^24kg!)

One of the answers spoke of trying to let go of something such that it might stay hovering in place! How interesting. It’s as if the object falls only because in the act of letting go a tiny push is given and the object accelerates as it falls, but, if it could be let go without that initial tiny push it might stay there in midair.

The truth is, that even as you hold the object in your hand it has weight. It has weight because the earth is pulling it downward even as you hand prevents it from falling. (This, by the way, is why weight is really the result of an upward push rather than a downward force!) So, the unbalanced force of gravity is always acting on the object whether you are holding it or not. It is even acting on the object when it is firmly on the ground!

But, do not forget, the object is also exerting an equal force (a force equal to its weight) on the earth pulling it upward. So, keep in mind that things fall because of gravity (The question of what gravity actually is can be addressed another day.) and they can fall up as well as fall down.

Answer 4

I think you have probably heard of the gravitational force, what pulls objects to the center of the earth. It was first studied by Newton, then Einstein. There are other theories, such as the string theory as to why atoms are attracted to each other. No one has fully discovered how and why gravity works the way it does. Until then, we will probably not be able to manipulate it, such as being able to float stuff.

Answer 5

I think stuffing something while floating is problematic. I know from personal experience that it is much easier with a turkey, for instance, if it and I and the stuffing are all firmly supported by horizontal surfaces and feeling at least moderately weighty. Aliens may not like turkey, I suppose.

Answer 6

Things fall because of matter warping spacetime into a low energy state. Objects want to move to this low energy state, which we see as attraction (gravity). I doubt you could build an antigravity machine because that would requre harnessing dark energy (a form of energy that acts as antigravity), which can't be physically done.

Answer 7

Yes, that force is Gravity...
A machine to stop gravity is called a vacuum...astronauts practice in a vacuum before going into space, where there is no gravity.

Answer 8

That was a question which Sir Isaac Newton used to ask...but only when he was a child...

Answer 9

GRAVITY!!!