There are two ways to increase the temperature of a body. One way is to put the body in contact with a hotter body, and the other way is to do work on the body. Work can be done on a body by compressing the body, as in the case of a gas, or by using the force of friction. By rubbing your hands together it is easy to see that friction generates heat, i.e., temperature changes. This raises the question: how many joules of mechanical energy are needed to produce 1 calorie of heat? Many experiments can be done to measure this quantity and the result is 4.18 joules. This is considered a fundamental constant, like the mass of an electron or the universal constant of gravity, G.

  1. What is mechanical energy? Name 4 forms of mechanical energy.
  2. Describe two experiments which will measure the so-called "mechanical equivalent of heat", 4.18 joules = 1 calorie.
  3. Before the development of theory of the conservation of energy and the molecular theory of matter, it was believed that all objects contain a weightless, invisible, odorless, substance called "caloric". When something burns the "caloric" is released. The hotter an object is the more "caloric" it contains. When a hot object comes in contact with a cold object "caloric" flows from the hot object to the cold object. Discuss the experimental facts that are consistent with and inconsistent with this theory.
  4. Suppose you add heat to one liter of water and the temperature rises 1 degree Celsius. If you add the same amount of heat to two liters of water, how much will the temperature rise?
  5. An average person will consume and expend 2000 kcal per day. How much heat is this in Joules? What is the rate at which heat is expended in watts?