# GCSE Science/Movement

How can we describe the way things move?

Motion has two basic properties, direction and speed.

Objects in our universe travel in three fundamental directions. We usually describe these directions, or axes, using the letters x, y and z. When we are describing motion close to, or with respect to, the Earth's surface we usually align the axes such that the z direction points vertically. Most people will then choose the x axis to point right and the y axis to point forwards (right-handed co-ordinate System). Motion in any other direction is the same as simultaneously moving in any of these three directions.

Speed is how fast an object covers a particular distance per unit of time. The units of distance are most commonly specified in meters or some power of ten multiple of meters (millimeter, kilometer, etc.), but other imperial units, such as inches and miles are sometimes used. Nearly everyone uses seconds, minutes, and hours as the unit of time. In scientific reports, seconds are used exclusively.

Together these two ideas form the notion of velocity, directed motion.

The language we use to describe motion in our universe is the vector, which exists in three dimensions. A vector is similar to an arrow in three dimensional space (i.e. it has a direction associated with it.) You will learn more about this in maths.