[جنون الفزياء]

1. What types of natural phenomena could serve as time standards?
2. Suppose that the three fundamental standards of the
metric system were length, density, and time rather than
length, mass, and time. The standard of density in this
system is to be defined as that of water. What considerations
about water would you need to address to make
sure that the standard of density is as accurate as
possible?
3. The height of a horse is sometimes given in units of
“hands.” Why is this a poor standard of length?
4. Express the following quantities using the prefixes given in
Table 1.4: (a) 3 ! 10"4 m (b) 5 ! 10"5 s (c) 72 ! 102 g.
5. Suppose that two quantities A and B have different dimensions.
Determine which of the following arithmetic operations
could be physically meaningful: (a) A ' B (b) A/B
(c) B " A (d) AB.
6. If an equation is dimensionally correct, does this mean
that the equation must be true? If an equation is not dimensionally
correct, does this mean that the equation cannot
be true?
7. Do an order-of-magnitude calculation for an everyday situation
you encounter. For example, how far do you walk or
drive each day?
8. Find the order of magnitude of your age in seconds.
9. What level of precision is implied in an order-of-magnitude
calculation?
10. Estimate the mass of this textbook in kilograms. If a scale is
available, check your estimate.
11. In reply to a student’s question, a guard in a natural history
museum says of the fossils near his station, “When I
started work here twenty-four years ago, they were eighty
million years old, so you can add it up.” What should the
student conclude about the age of the fossils?
QUESTIONS