A student writes: “When I rub my dry hands together on a cold morning, they warm up. However, when I repeat this with soapy water my hands don’t warm up as much.” Explain these observations by considering the energy stores and transfers involved.

Which of the following correctly describes what happens when an atomic bomb explodes? small pieces of fissionable material are joined and form a body with a mass greater than the critical mass, the relative number of neutrons escaping decreases, and a chain reaction and explosion result. large pieces of fissionable matter are brought together quickly and form a body with a mass smaller than the critical mass, the relative number of escaping neutrons increases, and a chain reaction and explosion result.