Question

What does strong force mean?

Answer 1

It is one of the four fundamental forces with a very short range.

Explanation:

There are `4` fundamental forces given below...
`color (green)(▪"Gravitational force")`
`color (green)(▪"Electromagnetic force")`
`color (green)(▪"Strong force")`
`color (green)(▪"Weak force")`

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As the name suggests strong force is really strong. It is more like a contact force because of its extremely short range.

We know that like charges repel each other and in a nucleus, there are a lot of it (except for hydrogen atom).

So, that means proton push each other away in a nucleus but yet protons somehow manage to keep themselves together.

It is clear that the force which holds the nucleus together is much stronger than the Electromagnetic repulsive force between protons.This force is strong nuclear force.

here, this force is carried by mesons.

Experiments show that strong force are about `100` times stronger than electromagnetic force.

This force holds the neighbouring protons together because of its short range.

This explains
`color (blue)(▪"why atoms are stable")`
`color (blue)(▪"short range of strong force"(10^-15m)`

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A simple experiment can demonstrate short range of strong force

Consider uranium atom (a heavy element), as the observations suggest it is unstable because of greater repulsive force, if strong force was stronger than electromagnetic force and with a good range as well then the atoms would have been even heavier and lot more stable but it isn't so.
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Consider 2 Protons separated by `1m` , they'll move apart from each other though force and velocity would be too less but yet observable. If strong force had a good range then those protons would have attracted further.

`--------------------`

Strong force also exists between quarks.
A proton & neutron are made up of smaller units called quarks

In a proton, there are 3 quarks (2 up and 1 down).
up quarks have a charge of `+2/3` and down with `-1/3`.
these quarks do repel each other as well but here gluon keeps bouncing between the quarks and hold them together. gluon actually glues sub-atomic particles. gluon is a massless particle so its speed is "c".

Watch these video about strong force