Glossary

Symbol for acceleration. Also A, the amplitude.

The rate of change in velocity with time, dv/dt. (a) Units of m.s^–2

A very useful system for locating where something is in space. We define perpendicular x, y, and z axes in space, crossing at a point called the origin, and can then express the location of anything by the distance we would have to go in the x, y, and z direction to get there from the origin.

Displacement

How far something is moved, usually along the x-axis. (x) Units of m.

Electron

A tiny lump of matter that has mass (9.1 × 10^-31 kg), charge (–1.6 × 10^-19 C) and spin (1/2). We can’t really say how big it is. A positively charged electron is called a positron.

Empirical

You will remember the meaning of this word better if you look it up for yourself.

symbol for energy. Units of Joules, J, equal to kg.m².s^–2

Energy

The capacity for an object - or a system - to do work. Total energy is the sum of the kinetic energy (from the velocity something is moving) and potential energy (which may be lots of different kinds). (E)

Symbol for force. Units of Newtons, N, equal to kg.m.s^–2

Force

The rate of change of momentum.(dp/dt) Also, anything that can make the momentum of something change. (F)

Frequency

How often an event that occurs at a regular interval occurs. The symbol for this in Physical Chemistry is the Greek letter nu, ν, and it is usually expressed in units s^–1.

Hooke’s Law

If you try to stretch or squash something, you will find a force resisting you that is proportional to how far you have stretch or squashed it already. This is very close to true for low values of stretching or squashing for a great number of things, including molecules. The equation is F = -kx where k is the force constant.

kilogram. The System Internationale unit of mass.

Kinetic Energy

The energy something has because it is moving. (K)

metre. The System Internationale unit of length. Also the symbol for mass.

Mass

The resistance an object has to being set in motion. If it takes a lot of energy to get it moving, it has a high mass. (m) Units of kg.

Momentum

How hard it is to stop an object that is moving already. (p)

Newton’s First Law

F = ma

Orbit

A relatively stable path traced out in space by a large object interacting with an even larger object: e.g, a spanner dropped from the International Space Station whirling around and around in Earth. It is deterministic: an equation for the orbit allows us to predict the position of the large object as a function of time.

Orbital

The equivalent of an orbit at the quantum scale. The ‘path’ traced out in space by a tiny object interacting with another tiny object: e.g., an electron in a chlorophyll molecule. It is probabilistic: an equation for the orbital allows us to predict the average position of the tiny object averaged over all times.

Position

Where something is at a particular time. (q) Usually expressed in Cartesian coordinates (x,y,z) or Spherical Polar Coordinates (r,θ,φ)

Potential Energy

The energy stored in a system due to its position, condition, or composition. (V)

Second. The System Internationale Unit for time.

Spherical Polar Coordinates

A very useful coordinate system for three dimensional systems where something is moving around something else. It expressed position in terms of the distance from the centre, r, and two angles, θ and φ. These coordinates are related to Cartesian coordinates like so:

x = rsinθ cosφ

y = rsinθ sinφ

z = rcosθ Velocity

The rate of change in position with time, dx/dt. (v) Units of m.s^–2

Weight

The force exerted by an object due to gravity.

Work

What Chris is doing right now.