33.2 The Four Basic Forces

Two intact (not ionized) hydrogen atoms are 10 cm apart. Which of the following are true?

1. Gravity, though very weak, is acting between them.
2. The neutral charge means the electromagnetic force between them can be ignored.
3. The range is too long for the strong force to be involved.
4. All of the above.

Consider four forces: the gravitational force between the Earth and the Sun; the electrostatic force between the Earth and the Sun; the gravitational force between the proton and electron in a hydrogen atom, and the electrostatic force between the proton and electron in a hydrogen atom. What is the proper ordering of the magnitude of these forces, from greatest to least?

1. gravity, Earth-Sun; elect…

Consider the Earth-Moon system. If we were to place equal charges on the Earth and the Moon, how large would they need to be for the electrostatic repulsion to counteract the gravitational attraction?

1. 5.1×10¹³ C
2. 5.7×10¹³ C
3. 6.7×10¹³ C
4. 3.3×10²⁷ C

An atomic nucleus consists of positively charged protons and neutral neutrons, so the electrostatic repulsion should destroy it by making the protons fly apart. This doesn't happen because:

1. The strong force is ~100 times stronger than electromagnetism.
2. The weak force generates massive particles that hold it together.
3. Electromagnetism is sometimes attractive.
4. Gravity is always attractive.

(a) Find the ratio of the strengths of the weak and electromagnetic forces under ordinary circumstances.

(b) What does that ratio become under circumstances in which the forces are unified?