Energy

A.  Energy is the ability to do work (or cause change)

1.  Two categories for energy:

a.  Kinetic energy

1)  The energy of motion.

2)  Formula:  KE = 1/2 m v^2

b.  Potential energy

1)  Stored energy.

2)  Formula:  PE = m g h

2.  Work is the transfer of energy through motion.

a.  For work to take place, a force must be exerted through a distance.

b.  Formula:  W = f d

c.  Unit is a joule (newton meter)

3.  The law of conservation of energy states that energy may change forms, but it cannot be created or destroyed.

4.  Most energy is ultimately converted into heat.

B.  Temperature and Heat

1.  Temperature is a measure of the average kinetic energy of the particles in a sample of matter.

2.  Thermal energy is the total energy of the particles in a material.

3.  Example:

a.  Two samples of 5g at 20 C have the same temperature.

b.  Those same samples together have twice as much thermal energy as only one.

4.  Heat

a.  Heat is the energy that flows from an area of higher temperature to an area of lower temperature.

b.  It always flows from warmer to cooler material.

C.  Measuring Thermal Energy

1.  Units

a.  The old unit was the calorie (cal).

b.  The new unit is the joule (J).

2.  Specific heat

a.  The amount of energy it takes to raise the temperature of 1 kg of material 1 degree Kelvin.

b.  Measured in J / kg K

c.  Materials with high specific heats require a lot of energy to be heated up, but release their heat slowly.

d.  Calorimeters measure specific heat.

e.  Formula:  Q = m T C(p)