Cod

I cannot figure out this problem involving gravity that I've been thinking about all day. As I understand it, gravity the natural force attraction exerted celestial bodies on objects. Basically, this means objects are pulled to Earth (celestial body). What I cannot understand is, how do we grow? Don't all aspects of the growth defy the laws of gravity?

I was thinking it had to do with force. Like a space shuttle launching, our bones and muscles use so much force on our bodies which makes us grow. Kind of like "pushing" us up. Any truth to this?

If my little theory isn't right, can someone explain it to me?


Any help is appreciated.

Asha'man

I think defy the laws of gravity is a gross misunderstanding. By your usage, standing up would also defy the law of gravity. (It doesn’t.)

In reality (localized to the surface of the Earth), gravity simply exerts a pull on you. Other forces are free to push and pull on you as well. The ground pushes up on you, your car pushes forward on you, etc. When you add up all these pushes and pulls, you find a total net force. If that force is very small, you stay in place. If the total force is higher in one direction, you accelerate in that direction.

I don’t see how growth is tied into this at all. The body is constantly dealing with external forces, and generating forces of it’s own. When you grow, you get a little taller. You also have to stretch your skin a little tighter to fit around your new size. But the forces opposing this are tiny, and easily overcome by our bodies.

On the other hand, when you eat (gotta eat to grow!), you have to lift your hand towards your mouth. Gravity is pulling your arm towards the ground, but your muscles are exerting a stronger force, pulling your arm upwards. The total net force ends up being “up”, so your arm rises. Gravity is still working just fine, but the muscles in your arm are simply stronger.

deano

Gravity is essentialy the same as kinetic energy,thus when we exert a kinetic force of our own,we can act against gravity.

relativity states that gravity curves space time,some how objects with mass create this curve.And the greater the mass the faster you fall down into this curve.try thinking in 4D to imagine it!.

perhaps some physicist would like to enlighten us on gravitons,and wave mechanics etc,cos i just read physics passingly and dont know much beyond quantum!

Shadowy Man

Yes, you do have to fight against gravity when you stand up, jump, lift something off the ground, etc.

However, gravity is not a very strong force. So, it's pretty easy to overcome it.

Jesse

There are four fundamental forces, gravity, electromagnetism, the strong force, and the weak force. The strong and weak force are mostly just involved with stuff going on in the atom's nucleus, so they don't ordinarily concern us--all the forces we see in everyday life are ultimately either electromagnetic or gravitational. The electromagnetic force is responsible for bonds between atoms and the way they interact at close range, as well as all chemical reactions. So stuff like friction, the normal force of the ground pushing you up to balance out gravity's pulling you down, the internal chemical reactions which cause your muscles to expand and contract, etc., are all ultimately manifestations of the electromagnetic force. If you jump up in the air, that's the electromagnetic force pushing matter in the opposite direction as gravity. I believe a completely electromagnetically neutral particle like a neutron would fall right through solid matter, although it's possible it'd eventually come close enough to another particle for the strong or weak force to stop its fall, I'm not sure.

Shadowy Man

Well, the neutron does have a magnetic moment, so it will interact with charged particles (at least if they are moving).

Jesse

OK, forget that last comment then...does that mean a neutrino has no magnetic moment, since it does pass through solid matter so easily?

Shadowy Man

I think there are currently only upper limits on the magnetic moment of the neutrino.

If it has one, it is most likely very, very small. I don't know exactly what produces a magnetic moment in neutral particles, but if it is related to mass at all, then you'd expect it to be very small in the neutrino.

Jesse

Maybe the magnetic moment of a neutron has to do with the fact that it's composed of quarks which themselves have fractional charges--the magnetic moment could be a consequence of the arrangement and motion of these quarks. If that's true, I don't know where the magnetic moment of a neutrino would come from, since a neutrino is supposed to be a fundamental particle not composed of anything smaller.