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Question

A ) what is meaning of gravity and define gravitation.

B) why is gravity have a value 9.8 ms^{-2 }but not Some 5 or 6 and write its derivevation.

C) write its uses and why is it weaker force than others.

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Solution

Gravity

2.

It means, if you let a body fall freely (on earth), then this is the rate at which it will gain in speed towards the ground. It's called the

after 1 sec - 9.81 m/s

after 2 secs - 19.62 m/s

after 3 secs - 29.43 m/s

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.

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In newtonian gravitation, the force of gravity between two bodies is given by Fm1m2=Gm1m2r2Fm1m2=Gm1m2r2, where m1m1 and m2m2 are the masses, r is the separation between them, and G is a constant. Since the radius of the earth is a pretty large value, we may safely ignore the effect of changes in r when performing our experiments close to the surface of the earth. So, g = 9.81 m/s is an accurate enough value for most numerical problems.

Personally, I use g = 10 m/s because 9.81 is just makes the calculations too involved.

3.

Because there’s no ‘anti gravity’ and because the range of gravity is infinite.

The weak force and the strong force are a lot stronger than gravity, but they are mediated in such a way that they don’t reach very far. To them, most of the universe is opaque: they will react with something before they get very far (like light would react with the electrons in opaque material).

Electromagnetism has the same range as gravity though, but while it’s stronger than gravity, it comes in two species minus and plus (for electrical charge) and north and south (for magnetic charge) and these two variants tend to negate eachother.

To give an example, let’s look at the field of different multipole.

A single charged particle gives a force that’s proportional to 1r2 1r2

An electrical dipole will give a force that’s proportional to 1r3 1r3 (this is an approximation that only works from a large distance, but note that it does not go as 1r21r2)

An electrical quadrupole will have an order lower as the dominant term: 1r4 1r4.

Etcetera.

So the attractive force of the one charged particle will almost completely be negated by the repulsive force of the opposite charged particle. Most objects tend to be neutral from the outside, but made up out of billions of particles, which means the electromagnetic field outside of it is very very small.

Conversely, all particles have only 1 gravitational charge (let’s call it positive). The charge for gravity is mass, and as far as we know, objects with negative mass don’t exist. As a result, an object is made up out of only positive charges, and these all stack.

So the electromagnetic field, due to the fact there’s 2 different charges, tends to be negated. The strong and the weak force simply don’t reach all that far.

As a side note. There’s another large difference between gravity and electromagnetism. For gravity, two equal charges (and all charges are equal), have an attractive force. For electrogmagnetism, two equal charges have a repulsive force.

As a result, electromagnetic-wise, matter tends to group together: it’s very energy efficient to have equal amounts of positive and negative charge, making the total object neutral. Objects of just one charge are almost impossible, because it would push itself apart.

Gravity wise, matter tends to group together as well, because the force is attractive. If there were such a thing as negative mass, then this would (probably) be repulsive to positive mass. One could imagine that if both negative and positive mass existed, it would just clump together in one large clump positive, and one large clump negative. Which might very well be a reason why we’ve never seen anything like negative mass in the first place.

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