33.2 The Four Basic Forces
Two intact (not ionized) hydrogen atoms are 10 cm apart. Which of the following are true?
- Gravity, though very weak, is acting between them.
- The neutral charge means the electromagnetic force between them can be ignored.
- The range is too long for the strong force to be involved.
- All of the above.
Explain why we only need to concern ourselves with gravitational force to describe the orbit of the Earth around the Sun.
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?
- gravity, Earth-Sun; electrostatic, Earth-Sun; gravity, hydrogen; electrostatic, hydrogen
- electrostatic, Earth-Sun; gravity, Earth-Sun; electrostatic, hydrogen; gravity, hydrogen
- gravity, Earth-Sun; gravity, hydrogen; electrostatic, hydrogen; electrostatic, Earth-Sun
- gravity, Earth-Sun; electrostatic, hydrogen; gravity, hydrogen; electrostatic, Earth-Sun
Deep within a nucleon, which is the stronger force between two quarks, gravity or the weak force? Why do you think so?
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?
- 5.1×1013 C
- 5.7×1013 C
- 6.7×1013 C
- 3.3×1027 C
What is the strength of the magnetic field created by the orbiting Moon, at the center of the orbit, in the system in the previous problem? (Treat the charge going around in orbit as a current loop.) How does this compare with the strength of the Earth's intrinsic magnetic field?
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:
- The strong force is ~100 times stronger than electromagnetism.
- The weak force generates massive particles that hold it together.
- Electromagnetism is sometimes attractive.
- Gravity is always attractive.
The atomic number of an atom is the number of protons in that atom's nucleus. Make a prediction as to what happens to electromagnetic repulsion as the atomic number gets larger. Then, make a further prediction about what this implies about the number of neutrons in heavy nuclei.
33.3 Accelerators Create Matter from Energy
Which of the below was the first hint that conservation of mass and conservation of energy might need to be combined into one concept?
- The Van de Graaff generator.
- New particles showing up in accelerators.
- Yukawa's theory.
- They were always related.
How fast would two 7.0-kg bowling balls each have to be going in a collision to have enough spare energy to create a 0.10-kg tennis ball? (Ignore relativistic effects.) Can you explain why we don't see this in daily situations?
Using only energy-mass considerations, how many K0 could a Z boson decay into? How many electrons and positrons could be produced this way?
A π+ and a π- are moving toward each other extremely slowly. When they collide, two π0 are produced. How fast are they going? (Ignore relativistic effects.)
- Barely moving
- 1.0×107 m/s
- 2.0×107 m/s
- 7.8×107 m/s
Assume that when a free neutron decays, it transforms into a proton and an electron. Calculate the kinetic energy of the electron.
33.4 Particles, Patterns, and Conservation Laws
When a π- decays, the products may include:
- A positron.
- A muon.
- A proton.
- All of the above.
Notice in Table 33.2 that the neutron has a half-life of 882 seconds. This is only for a free neutron, not bound with other neutrons and protons in a nucleus. Given the other particles in the table, and using both their charge and masses, what do you think the most likely decay products for a neutron are? Justify your answer.
33.5 Quarks: Is That All There Is?
How many pointlike particles would an experiment scattering high energy electrons from any meson discover within the meson?
In this figure, a K- initially hits a proton, and creates three new particles. Identify them, and explain how quark flavors are conserved.