1.1 The scope and scale of physics  (Page 7/12)

What is physics?

Some have described physics as a “search for simplicity.” Explain why this might be an appropriate description.

If two different theories describe experimental observations equally well, can one be said to be more valid than the other (assuming both use accepted rules of logic)?

What determines the validity of a theory?

Certain criteria must be satisfied if a measurement or observation is to be believed. Will the criteria necessarily be as strict for an expected result as for an unexpected result?

Can the validity of a model be limited or must it be universally valid? How does this compare with the required validity of a theory or a law?

Find the order of magnitude of the following physical quantities. (a) The mass of Earth’s atmosphere: $5.1\times {10}^{18}\text{kg;}$ (b) The mass of the Moon’s atmosphere: 25,000 kg; (c) The mass of Earth’s hydrosphere: $1.4\times {10}^{21}\text{kg;}$ (d) The mass of Earth: $5.97\times {10}^{24}\text{kg;}$ (e) The mass of the Moon: $7.34\times {10}^{22}\text{kg;}$ (f) The Earth–Moon distance (semimajor axis): $3.84\times {10}^8\text{m;}$ (g) The mean Earth–Sun distance: $1.5\times {10}^{11}\text{m;}$ (h) The equatorial radius of Earth: $6.38\times {10}^6\text{m;}$ (i) The mass of an electron: $9.11\times {10}^{\mathrm{-31}}\text{kg;}$ (j) The mass of a proton: $1.67\times {10}^{\mathrm{-27}}\text{kg;}$ (k) The mass of the Sun: $1.99\times {10}^{30}\text{kg.}$

Use the orders of magnitude you found in the previous problem to answer the following questions to within an order of magnitude. (a) How many electrons would it take to equal the mass of a proton? (b) How many Earths would it take to equal the mass of the Sun? (c) How many Earth–Moon distances would it take to cover the distance from Earth to the Sun? (d) How many Moon atmospheres would it take to equal the mass of Earth’s atmosphere? (e) How many moons would it take to equal the mass of Earth? (f) How many protons would it take to equal the mass of the Sun?

Roughly how many heartbeats are there in a lifetime?

A generation is about one-third of a lifetime. Approximately how many generations have passed since the year 0 AD?

Roughly how many times longer than the mean life of an extremely unstable atomic nucleus is the lifetime of a human?

Calculate the approximate number of atoms in a bacterium. Assume the average mass of an atom in the bacterium is 10 times the mass of a proton.

(a) Calculate the number of cells in a hummingbird assuming the mass of an average cell is 10 times the mass of a bacterium. (b) Making the same assumption, how many cells are there in a human?

Assuming one nerve impulse must end before another can begin, what is the maximum firing rate of a nerve in impulses per second?

About how many floating-point operations can a supercomputer perform each year?

Roughly how many floating-point operations can a supercomputer perform in a human lifetime?