7. Trace the energy supply of the body back to the sun.

8. Why must both oxygen and food be introduced into the body in order to
supply it with energy?

9. How may overwork and overexercise diminish the energy supply of the
body?

10. How may one increase the amount of his energy?



PRACTICAL WORK


*Suggested Experiments.*—1. The change of kinetic into potential energy
may be shown by stretching a piece of rubber, by lifting a weight, and by
separating the armature from a magnet.

2. The change of potential into kinetic energy may be shown by letting
weights fall to the ground, by releasing the end of a piece of stretched
rubber, and by burning substances.

3. The change of one form of kinetic energy to another may be illustrated
by rubbing together two pieces of wood until they are heated, by ringing a
bell, and by causing motion in air or in water by heating them. If
suitable apparatus is at hand, the transformation of electrical energy
into heat, light, sound, and mechanical motion can easily be shown.

4. A weight connected by a cord with some small machine and made to run