91Ó°ÊÓ

Astronomers sometimes measure distances in astronomical units, where \(1 \mathrm{AU}=1.496 \times 10^{11} \mathrm{~m},\) the mean distance from Earth to Sun. Why is this useful for distances within our solar system?

Describe a situation in which you might find it practical to use a non-SI unit

What are the disadvantages of using a prototype (a piece of metal) for the standard kilogram?

Nanotechnology (which includes building small-scale machines and the electronic circuit boards inside computers) has gained a lot of attention recently. Why do you think the word "nanotechnology" was chosen?

Explain the difference between dimensions and units.

Radio signals used to communicate with spacecraft travel at the speed of light. What problems do you think might arise if scientists want to send a series of signals to maneuver a spacecraft into orbit around Saturn?

Can you add or subtract quantities with different units? Can you multiply or divide quantities with different units?

Ten million \(\mathrm{kg}\) can be written as (a) \(10^{13} \mathrm{~g}\); (b) \(10^{10} \mathrm{~g}\); (c) \(10^{7} \mathrm{~g}\); (d) \(10^{6} \mathrm{~g}\).

(b) \(\mathrm{km} / \mathrm{h} ;\) (c) \(\mathrm{km} / \mathrm{s} ;\) (d) \(\mathrm{m} / \mathrm{s}\). The SI unit of speed is (a) \(\mathrm{mi} / \mathrm{h}\)

The age of the universe is approximately 13.7 Gy. This is approximately (a) \(4.3 \times 10^{11} \mathrm{~s} ;\) (b) \(4.3 \times 10^{14} \mathrm{~s}\) (c) \(4.3 \times 10^{17} \mathrm{~s}\) (d) \(4.3 \times 10^{20} \mathrm{~s}\)