Why do this problem?
This problem places units in an interesting context which can lead
on to other problems. It requires relatively little technical
skill, allowing students to focus solely on the process of changing
Discuss the problem as a class. Is everyone familiar with each of
the units mentioned? Throughout, encourage numerical order of
magnitude checks of the answers.
- Before changing units, do you expect the answer to be
numerically larger or smaller after the change?
- Relative to the natural scales of the universe are we small,
Consider the meaning of the statement 'the natural scales for the
universe'. Relate these units to everyday objects. Work out the
ratios for a person / a proton/ the sun / the galaxy / a neutron
star in the natural units. How do they compare G, c, and h?
You could treat this simply as a change of units question.