Fundamental Terms of Physics

Energy, Work, and Displacement

Energy is the ability to do work. Work is the energy transferred to an object (force) that causes a displacement. A displacement is the measure of the distance moved in a specific direction, or the shortest distance from an initial to a final position. A simple way to think of work is as the amount of energy given to or taken away from an object.

Distance vs. Displacement

Joules, Force, and Newtons

Energy and work are most commonly measured in joules (JJ). One joule is equal to the energy required for one newton (NN) of force to perform a displacement of one meter (mm), or J=NmJ=Nm.

Force is energy transferred to an object (a "push" or a "pull") that will change the motion of an object, if unopposed by another force. Force is measured in Newtons. One newton is the force required to accelerate one kilogram (kgkg) one meter per second squared, or 1N=1kg1m1s21N = \frac{1kg*1m}{1s^2}. The equation for force can also be written as the product of mass (MM) and acceleration (AA), or F=MAF=MA.

Video: How Much Energy is One Joule?

Mass, Velocity, and Acceleration

Mass is the amount of matter that makes up an object. Mass is measured in kilograms (kgkg). A kilogram was originally defined to equal to the mass of one litre of water, or 1,000 cubic centimeters of water (thus 1g1g is the mass of 1cm31cm^3 of water). It's still useful to think of kilogram as defined this way; however the formal definition of kilogram is more complicated.

Velocity is the distance (dd) traveled in a given direction over time (tt), or V=d/tV=d/t and is often expressed as meters per second (m/sm/s).

Acceleration is the rate of change in velocity (VV) over time (TT), or A=ΔV/ΔTA=\Delta{V}/\Delta{T}, in other words acceleration is how much an object is speeding up, slowing down, or changing direction.

Video: Acceleration, One-Dimensional Motion

Kinetic and Potential Energy

  • Kinetic energy is the energy an object possesses by being in motion (moving)
  • Potential energy is the energy an object has by being at rest (not moving)

Gravitational Potential Energy

Gravitational Potential Energy is the energy an object has by being at some height and would be converted to kinetic energy when the object is dropped. The force of Gravity on Earth (GG) is constant at 9.8m/s29.8m/s^2, therefore to calculate the gravitational energy of an object, we can use GG as the value for force, the object's height (HH) as the distance, and the objects mass (MM) for the mass, or: J=MGHJ=MGH.

Physics Resources

Deeper Knowledge on Physics

Angular Motion

The basics of angular motion


Energy that results from charged particles

Mechanical Advantage

Learn about mechanical advantage

Power (Physics)

Energy that results from charged particles


Learn about torque: Force that causes an object to rotate around an axis.

Physics Knowledge Graph