Course title

Energy

Dr. Walt Volland, revised March 25, 2005 all rights reserved 1997-2005

 

 

Energy is one of the most important concepts in science. Physical and chemical changes naturally occur to produce a condition of lowest or minimum energy. Water runs down hill because it is moving to minimum energy. Water flows down hill because it is flowing to a lower energy position. Gravity determines the potential energy of the water. Water at higher elevations has higher potential energy. When the water flows down hill the potential energy decreases as the water reaches lower and lower elevations.

Energy units are calories, Kilocalories, and Joules. One calorie is the amount of heat needed to warm 1 gram of water by one degree Celsius.

There are two classes of energy, kinetic energy and potential energy. The total energy of anything is the sum of these two. Thermal energy, electrical energy, sound energy, light energy, etc are all different ways we observe kinetic and potential energy.
Total energy = kinetic energy + potential energy

A descriptive definition for kinetic energy is "Energy due to motion". Something has kinetic energy because it has mass and it is moving. The mathematical definition for kinetic energy is shown here. The formula shows that high kinetic energy goes with high speeds and masses. Of course if an object is not moving it has no kinetic energy. The formula also shows that if there are two vehicles, one large and one small, both moving at 60 miles per hour the large one will have more kinetic energy.

A descriptive definition for potential energy is "Energy due to position". Potential energy exists because of the location of an object in a force field such as a gravitation, magnetic, or electric field.

The formula here shows the potential energy for an object with mass "m" in the earth's gravitational field. The force of the earth's gravitation acts on an object through the "g" term. Maybe you have heard of "g's" when people describe accelerating, racing, or flying. The "h" represents the height above a reference level. A book sitting on a table has less potential energy than a book on the ledge of an overhead shelf. Similar formulas exist for determining the potential energy for magnets in magnetic fields and charges in electric fields.

An ove riding energy concept is that energy is conserved. The law of conservation of energy says "Energy is neither created nor destroyed". This means energy is only transferred and dissipated. High concentrations of energy are useful. Low concentrations of energy are less useful. Flames for example are concentrated spaces of high energy concentration. Flames are able to make reactions occur because flames can transfer energy to cooler objects.
Practice exercises are on the next page.