Energy and Society: Work, Power, and Conservation

Mechanical Work (W)

when you apply a force to an object that causes the object to displace in the direction of the force or a component of the force

Joule (J)

a unit of energy

Work Equation

W = F • d

Zero Work

occurs when the vertical component does no work because the angle is 90°

Generalized Work Equation

W = F cos(θ) where θ is the angle between the force and displacement

Positive Work

occurs when the force or component of force is in the same direction as displacement

Negative Work

occurs when the force or component of force is in the opposite direction as displacement

Work when Raising or Lowering Objects

the force is equal to the force of gravity

Force of Gravity

F₁ = F₂ = mg

Mechanical Energy

energy possessed by objects that are primarily affected by the force of gravity and frictional forces

Radiant Energy

energy possessed by oscillating electric and magnetic fields (waves)

Gravitational Energy

energy possessed by objects that are affected by the force of gravity; applies to all objects on Earth (and the Universe)

Electric Energy (static)

energy possessed by accumulated static charges

Electric Energy (current)

energy possessed by flowing charges

Thermal Energy

energy possessed by randomly moving atoms and molecules

Sound Energy

energy possessed by large groups of oscillating atoms and molecules (waves)

Nuclear Energy

energy possessed by protons and neutrons in atomic nuclei

Elastic Energy

energy possessed by materials that are stretched, compressed, or twisted and tend to return to their original shape

Chemical Energy

energy associated with bonds in molecules

Energy Transformation

the change of energy from one type to another

Law of Conservation of Energy

in energy transformations, the total amount of energy is constant; energy is neither created nor destroyed

Mechanical Energy Total Equation

E_total = E_g + E_k = m • g • h + 1/2 • m • v^2

Example of Diver

consider a 65 kg diver on a 10 m platform

Gravitational Energy

Energy possessed by an object due to its position in a gravitational field.

Kinetic Energy

Energy that an object possesses due to its motion.

Efficiency

The amount of useful energy produced in an energy transformation expressed as a percentage of the total amount of energy used.

Waste Energy

Energy that is not transformed into useful energy.

Thermal Energy

The most common form of waste energy.

Energy Resources

Energy-rich substances such as crude oil and natural gas.

Non-Renewable Energy Resource

A substance that cannot be replenished as it is used in energy-transforming processes.

Fossil Fuel

Fuel produced by the decayed and compressed remains of plants that lived hundreds of millions of years ago.

Nuclear Energy

Form of energy produced by interactions in the nucleus of atoms.

Nuclear Fission

The decomposition of large, unstable nuclei into smaller, more stable nuclei.

Nuclear Fusion

The combination of small atomic nuclei to form larger atomic nuclei.

Renewable Energy Resource

A substance with a limited supply or a supply that can be replenished as it is used in energy-transforming processes.

Solar Energy

Radiant energy from the Sun.

Passive Solar Design

Building design that uses the Sun's radiant energy directly for heating.

Photovoltaic Cell

A device that transforms radiant energy into electrical energy.

Hydroelectricity

Electricity produced by transforming the kinetic energy of rushing water into electrical energy.

Power

The rate at which energy is transformed, or the rate at which work is done.

Power Rating

The maximum power of an electrical device.

Kilowatt (kW)

A unit of power equal to 1000 watts.

Cost of Electricity

Determined by the devices being used, the power rating of each device, and the total amount of time each device is used.

Kilowatt Hours (kWh)

A unit of electricity use measured by the amount of energy consumed.