Energy

Racing car on dirt track

Energy

Energy is the "stuff" that allows things to happen or change. It's like the fuel in a car that makes it go or the electricity that powers your phone. In physics, we use the term "energy" to describe this ability to make things happen or do work.

Equations on this page:
Kinetic Energy, Gravitational Potential Energy, Power with Work Done, and Efficiency.




What is an energy store?

Apple falling from a treeAn energy store is a way of talking about the different types of energy something can have. It helps us understand how energy is kept in objects or systems. For instance, something can have energy because it's moving, or because it's up high, or even because it's hot. There are 8 types of energy stores these are:

  • Thermal Energy: Energy is associated with the motion of particles in matter, and is also known as heat energy.
  • Kinetic Energy: Energy associated with the motion of an object.
  • Gravitational Potential Energy: Energy stored in an object due to its position in a gravitational field.
  • Elastic Potential Energy: Energy stored in an object when it is stretched or compressed.
  • Chemical Energy: Energy stored in the bonds between atoms and molecules.
  • Nuclear Energy: Energy stored in the nucleus of an atom, and released through nuclear reactions.
  • Electrostatic Energy: Energy stored in the electric fields created by charged particles.
  • Magnetic Energy: Energy stored in the magnetic fields created by magnets and moving charged particles.

What is energy transfer?

Energy transfer is the movement of energy from one store or object to another. Energy transfer can occur in many different ways, including through the transfer of heat, work, or electromagnetic radiation.

For example, when you touch a hot stove, thermal energy is transferred from the stove to your hand through conduction. When a car accelerates, the engine converts chemical energy from fuel into kinetic energy of the car.

Energy transfer is subject to the laws of thermodynamics, which govern how energy can be transferred and transformed between different forms. These laws dictate that energy can neither be created nor destroyed, but only transferred or transformed from one form to another.

The conservation of energy principle is a basic law in physics that states that energy can be transferred usefully, stored or dissipated but can never be created nor destroyed. This principle is also known as the first law of thermodynamics.

What is energy measured in?

Energy is measured in Joules (j). 1000 J = 1kJ (kilo-joule).

What is a closed system?

A closed system is somewhere where energy does not enter or leave.




EQUATION - Kinetic Energy

An object that is moving has energy stored in its kinetic energy store. This energy store depends on the object's mass and speed.

Kinetic Energy formula

Calculating Kinetic energy

EQUATION - Gravitational Potential Energy

An object that is raised has energy stored in its gravitational potential energy store. This energy store depends on the objects, mass height and strength of the gravitational field.

Gravitational Potential Energy formula

Calculating Gravitational Potential Energy

EQUATION - Power with work done

Power is the rate of doing work or rate of energy transfer. Power is measured in watts. A powerful machine quickly moves a lot of energy in a short time.

Power with work done formula

Calculating Power and work done

EQUATION - Efficiency

Efficiency measures the amount of energy wasted when transferred from one store to another. The less energy wasted the more efficient a device is. When the energy transferred is wasted we call this dissipated energy.

No device is 100% efficient as the energy is usually transferred to thermal energy stores. One exception of this is an electric heater because all of the energy is transferred to useful thermal energy stores.

Efficiency formula

Efficiency




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