How is energy conserved

Society has to get energy from somewhere, although there are many sneaky places to get it from some sources are primary fuels and some sources are primary energy flows. Early in the 20 th century, Einstein figured out that even mass is a form of energy this is called mass-energy equivalence.

The amount of mass directly relates to the amount of energy, as determined by the most famous formula in physics:. To learn more about the physics of the law of conservation of energy, please see hyperphysics or for how this relates to chemistry please see UC Davis's chem wiki.

Fossil Fuels. Nuclear Fuels. Nuclear energy is transformed into the energy of sunlight, into electrical energy in power plants, and into the energy of the heat transfer and blast in weapons.

Atoms and molecules inside all objects are in random motion. This internal mechanical energy from the random motions is called thermal energy , because it is related to the temperature of the object. These and all other forms of energy can be converted into one another and can do work. Table 1 gives the amount of energy stored, used, or released from various objects and in various phenomena. The range of energies and the variety of types and situations is impressive.

You will find the following problem-solving strategies useful whenever you deal with energy. The strategies help in organizing and reinforcing energy concepts. In fact, they are used in the examples presented in this chapter. The familiar general problem-solving strategies presented earlier—involving identifying physical principles, knowns, and unknowns, checking units, and so on—continue to be relevant here.

Step 1. Determine the system of interest and identify what information is given and what quantity is to be calculated.

A sketch will help. Step 2. Examine all the forces involved and determine whether you know or are given the potential energy from the work done by the forces.

Then use step 3 or step 4. Step 3. If you know the potential energies for the forces that enter into the problem, then forces are all conservative, and you can apply conservation of mechanical energy simply in terms of potential and kinetic energy. Step 4.

If you know the potential energy for only some of the forces, possibly because some of them are nonconservative and do not have a potential energy, or if there are other energies that are not easily treated in terms of force and work, then the conservation of energy law in its most general form must be used.

In most problems, one or more of the terms is zero, simplifying its solution. Do not calculate W c , the work done by conservative forces; it is already incorporated in the PE terms. Step 5. You have already identified the types of work and energy involved in step 2. Before solving for the unknown, eliminate terms wherever possible to simplify the algebra.

Then solve for the unknown in the customary manner. Step 6. Check the answer to see if it is reasonable. Once you have solved a problem, reexamine the forms of work and energy to see if you have set up the conservation of energy equation correctly. For example, work done against friction should be negative, potential energy at the bottom of a hill should be less than that at the top, and so on. Also check to see that the numerical value obtained is reasonable. Figure 1. Solar energy is converted into electrical energy by solar cells, which is used to run a motor in this solar-power aircraft.

The conservation of energy is an absolute law, and yet it seems to fly in the face of things we observe every day. A battery produces power. A nuclear bomb creates an explosion. Each of these situations, however, is simply a case of energy changing form. The law of conservation of energy , also known as the first law of thermodynamics, states that the energy of a closed system must remain constant—it can neither increase nor decrease without interference from outside.

The universe itself is a closed system, so the total amount of energy in existence has always been the same. The forms that energy takes, however, are constantly changing.

Potential and kinetic energy are two of the most basic forms, familiar from high school physics class: Gravitational potential is the stored energy of a boulder pushed up a hill, poised to roll down. Kinetic energy is the energy of its motion when it starts rolling. The sum of these is called mechanical energy. The heat in a hot object is the mechanical energy of its atoms and molecules in motion. Chemical energy is another form of potential energy stored in molecular chemical bonds.

It is this energy, stockpiled in your bodily cells, that allows you to run and jump. Other forms of energy include electromagnetic energy, or light, and nuclear energy—the potential energy of the nuclear forces in atoms. There are many more. Fire is a conversion of chemical energy into thermal and electromagnetic energy via a chemical reaction that combines the molecules in fuel wood, say with oxygen from the air to create water and carbon dioxide.

It releases energy in the form of heat and light.