Nuclear Size, Density, and Forces
Why nuclei are so compact
Nuclear size
A nucleus is extremely small, with a radius roughly given by , where is about and .
High density
Because nearly all the atom's mass is packed into such a tiny volume, nuclei are incredibly dense. This is one reason nuclear matter is physically very different from ordinary matter.
The strong nuclear force
Protons repel each other electrically, but inside the nucleus an attractive force called the strong nuclear force binds nucleons together. It is very strong at short distances but acts only over a very small range.
Important idea
The strong nuclear force can overcome the electric repulsion between protons, but only when nucleons are very close together.
Electrical force vs strong nuclear force
Electrical force
- Acts between charged particles
- Can be long-range
- Protons repel each other
Strong nuclear force
- Acts between nucleons at very short range
- Is attractive in the nucleus
- Helps bind nuclei
Why don't all protons in a nucleus fly apart?
The attractive strong nuclear force overcomes proton-proton electric repulsion at nuclear distances.
Correct answer: Because the strong nuclear force binds nucleons together
What is the approximate unit often used for nuclear distances?
Nuclear sizes are commonly measured in femtometers, where .
Correct answer: femtometer
The strong nuclear force is most important at what kind of distance?
The strong force is a short-range force that acts within the nucleus.
Correct answer: Short distances inside the nucleus