When a rubber ball dropped from rest bounces off the floor, its direction of motion is reversed becaue (A) energy of the ball is conserved
(B) momentum of the ball
(C) the floor exerts a force on the ball that stops its fall and then drives it upward
(D) the floor is in the way and the ball has to keep moving
(E) none of the above

In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.[note 1] Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton.

Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.

Mass and energy are closely related. Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy. For example, after heating an object, its increase in energy could be measured as a small increase in mass, with a sensitive enough scale.

Living organisms require energy to stay alive, such as the energy humans get from food. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the sun and the geothermal energy contained within the earth.

Explanation:

Some forms of energy (that an object or system can have as a measurable property)

Type of energyDescription

Mechanicalthe sum of macroscopic translational and rotational kinetic and potential energies

Electricpotential energy due to or stored in electric fields

Magneticpotential energy due to or stored in magnetic fields

Gravitationalpotential energy due to or stored in gravitational fields

Chemicalpotential energy due to chemical bonds

Ionizationpotential energy that binds an electron to its atom or molecule

Nuclearpotential energy that binds nucleons to form the atomic nucleus (and nuclear reactions)

Chromodynamicpotential energy that binds quarks to form hadrons

Elasticpotential energy due to the deformation of a material (or its container) exhibiting a restorative force

Mechanical wavekinetic and potential energy in an elastic material due to a propagated deformational wave

Sound wavekinetic and potential energy in a fluid due to a sound propagated wave (a particular form of mechanical wave)

Radiantpotential energy stored in the fields of propagated by electromagnetic radiation, including light

Restpotential energy due to an object's rest mass

Thermalkinetic energy of the microscopic motion of particles, a form of disordered equivalent of mechanical energy

Main articles: History of energy and timeline of thermodynamics, statistical mechanics, and random processes

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