General Physics II

Internal energy is the energy of the atoms and molecules -- translational energy, rotational energy, and vibrational energy.

Heat is internal energy that is exchanged between two objects due to their difference in temperature.

Heat always transfers, or flows, from a body at higher temperature to one at lower temperature.

Heat and internal energy are obviously connected or associated; but they are not the same thing. Heat is a transfer of internal energy due to a difference in temperature. This is analogous to the connection between work and energy. When you do work on a system you change its energy. Work is a transfer of energy.

UNITS

One calorie, cal, is the amount of heat necessary to raise the temperature of 1.0 g of water from 14.5^oC to 15.5^oC

Notice that one "food calorie", 1 Cal, is one thousand "heat calories"; that is,

1 Cal = 1000 cal = 1 kcal

One British thermal unit, BTU or btu, is the amount of heat necessary to raise the temperature of 1.0 pound (lb) of water from 63^oF to 64^oF

The Mechanical Equivalent of Heat

Work and energy are related. Work can raise the temperature of a system.

Joule -- after whom the SI unit of energy is named -- did early experiments showing the connection between heat and work. He found that direct connection to be

1 cal = 4.186 J

This is known as the Mechanical Equivalent of Heat. You will do a lab experiment later this semester in which you measure this for yourself.

Ch20; Heat and the First Law of Thermodynamics

Heat and Internal Energy