Chapter 7 ENERGY

Potential Energy An object can store energy as the result of its position. For example, the heavy ball of a demolition machine is storing energy when it is held at an elevated position. This stored energy of position is referred to as potential energy. Similarly, a drawn bow is able to store energy as the result of its position. When assuming its usual position (i.e., when not drawn), there is no energy stored in the bow. Yet when its position is altered from its usual equilibrium position, the bow is able to store energy by virtue of its position. This stored energy of position is referred to as potential energy.

Potential energy is the stored energy of position possessed by an object.

KINETIC ENERGY Energy from moving objects Much of that kinetic energy goes to waste. All moving objects have energy due to their motion. The energy a body has due to its motion is called kinetic energy.

First Law of Energy Energy can not be created Energy can not be destroyed Energy can only change forms

To scientists, "conservation of energy" does not mean saving energy. Instead, the law of conservation of energy says that energy is neither created nor destroyed. When we use energy, it doesn't disappear. We change it from one form of energy into another.

During all this moving and transforming the total amount of energy never changes. That's it! I've done it! That's the first law of thermodynamics! Ta da! Energy changes form and moves from place to place but the total amount doesn't change. Simple, eh?

Other ways to say it: It's conservation of energy. Energy is conserved during any and every process or transformation or "happening". Energy doesn't pop into existence from nowhere. Energy doesn't pop out of existence into nowhere. Energy is neither created nor destroyed (the old fuddy duddy way of saying it). "Energy in" equals "energy stored" plus "energy out" (if no energy is stored, then "Energy in" equals "Energy out").

You may have already heard that the 1st Law says energy is "always conserved". So why are we always saying we need to conserve more energy if it is "always conserved" already? When we say energy is always conserved we mean the total amount of energy in any process or reaction never changes. When we tell ourselves to conserve energy we mean to use less of it by doing things like driving more fuel efficient cars, or insulating our houses better.

A car engine burns gasoline, converting the chemical energy in gasoline into mechanical energy. Solar cells change radiant energy into electrical energy. Energy changes form, but the total amount of energy in the universe stays the same.

Vibration Movement back and forth

2 nd Law of Energy "Energy efficiency" is the amount of useful energy you get from any type of system. A perfectly energy-efficient machine would change all the energy put in it into useful work. In reality, converting one form of energy into another form always involves a loss of useable energy.

Lost as Heat

In fact, most energy transformations are not very efficient. The human body is a good example. Your body is like a machine, and the fuel for your machine is food. Food gives you the energy to move, breathe, and think. But your body isn't very efficient at converting food into useful work. Your body is less than 5% efficient most of the time. The rest of the energy is lost as heat.

Nonrenewable Energy supplies are limited. Petroleum, for example, was formed millions of years ago from the remains of ancient sea plants and animals. We can't make more petroleum in a short time.

Nonrenwable About 93% of the energy consumed in the United States comes from non-renewable energy sources, which include uranium ore and the fossil fuels — Coal natural gas petroleum.

Petroleum

Ink Crayons bubble gum dishwashing liquids deodorant Eyeglasses records tires Ammonia heart valves.

Natural Gas

Coal

Renewable Energy Renewable energy sources can be replenished in a short period of time. The five renewable sources used most often are: Biomass — including wood and wood waste, municipal solid waste, landfill gas, and biogas, ethanol, and biodieselBiomassethanol biodiesel Water (hydropower)hydropower Geothermal Wind Solar Provide 7% of the energy used in the United States. Most renewable energy goes to producing electricity.

Renewable energy plays an important role in the supply of energy. When renewable energy sources are used, the demand for fossil fuels is reduced. Unlike fossil fuels, non-biomass renewable sources of energy (hydropower, geothermal, wind, and solar) do not directly emit greenhouse gases.

Why are we not using it? More expensive to produce and use than fossil fuels. Expensive to build power lines to the cities where the electricity they produce is needed. Limited by the fact that they are not always available — cloudy days reduce solar power; calm days reduce wind power; and droughts reduce the water available for hydropower.