Physics 169 Midterm 1

How much weaker is gravity compared to the other 3 forces?

10^33 times weaker than the weakest force

What are the 4 forces?

Gravity, electromagnetism, strong force, and weak force.

What is the source of gravity?

Mass.

Why is gravity the weakest force in theory but still strong in the context of our universe?

1) Mass can only be positive, and thus so is gravity. Its pull can weaken indefinitely but never reach 0. 2) Gravity is long-range.

What is the formula for gravity/what does each symbol mean?

What is G in the context of gravity?

The gravitational constant. It is equal to 6.67×10^-8 in cgs units.

Source of electromagnetism?

Charges.

How is electromagnetism similar to gravity?

• It has a universal constant.

• It depends on the distance b/w 2 bodies

How is electromagnetism different from gravity?

• It can be either attractive or repulsive due to positive / negative charges

• It is 10^ 36 times stronger

What kind of field do stationary charges produce? (non-moving protons/electrons)

Electric field.

What kind of field do moving charges produce?

Magnetic field.

Why is electromagnetism useful?

• creates electromagnetic radiation (light from the sun (visible light), x-rays, gamma rays, microwaves, etc.)

• Shapes smaller bodies (terrestrial planets, asteroids, comets, etc.). Though gravity holds these things together.

• Responsible for chemical processes and basically all of biology because it drives chemical reactions.

What does the strong force do?

• binds matter together with gluons (quarks combine into protons and neutrons)

• Allows for transmutation. (turning hydrogen into heavier elements at the beginning of the universe)

What property do particles have that lets them experience strong force?

The color charge. What has it?

YES: quarks, protons, neutrons, atomic nuclei

NO: electrons, photons, neutrinos

How much stronger is the strong force compared to electromagnetism and gravity?

10² (100 times) stronger than electromagnetism and 10^ 38 times stronger than gravity. This means that nuclear reactions are much more powerful than chemical reactions, hence atomic warfare, etc.

What is the source of the strong force?

Gluons. Specifically, gluons let the quarks combine to create protons, neutrons and atomic nuclei

What does the weak force do?

• it is kind of obscure

• 10^5 (100,000 times weaker than than the strong force

• Helps with specific transmutations/radioactive decay (neutrons emit protons and electrons in beta decay)

• It is one of the two forces that can interact w dark matter (the other one is gravity)

Order of strength: 4 forces

1. Strong force

2. Electromagnetism

3. Weak force

4. Gravity

What are the carrying particles for each force?

• Strong force: gluons (cause quarks to bind)

• Electromagnetism: photons (massless, basic unit of light and all other electromagnetic radiation)

• Weak force: W and Z bosons (have mass, cause radioactive decay and can work over small distances)

• Gravity: gravitons, just a theoretical concept

Speed Formula