# 1.01 Introduction to Mechanics

Some basic definitions

## Physical objects:

These are tangible things that we can touch and sense, they include the familiar everyday objects that we see around us as well as the tiny molecules and atoms from that they are made.

## Matter and mass:

Matter is the name given to the basic substance that all physical objects are made from. The amount of matter an object contains is referred to as its mass. Mass (m) is measured in units called kilograms (kg)

In everyday language very large objects (e.g. objects that have a very large volume or even objects that are just very tall) are often referred to as massive. In Physics the term massive refers specifically to an object's mass and not to it's size. It is not uncommon to find situations were the smaller of two objects is actually more massive (i.e. the smaller object contains more mass. This point is covered in more detail in the section on "Density".)

## Space and Volume:

Space is an empty void* through which physical objects can move. In Mechanics we are interested in specifying the location of objects in space (using co-ordinates) and also in the amount of space an object takes up (ie volume (V)). Volume is measured in cubic metres (also called metres cubed) (m3)

Note: We describe space as having three dimensions. This simply means that an object in space can move in three unique directions. e.g. up/down, left/right or forward/backward, or a path which combines movement in two or three dimensions simultaneously
(* in more advanced studies the nature of space is shown to be more complicated than stated here, however this description will be sufficient to study the mechanics that will be presented in the following sections)

## Forces:

Force is a term used to describe the attraction or repulsion between objects that are separated by a distance across empty space. (Apart from this action forces are invisible and intangible i.e. the attraction or repulsion that they produce is the only evidence of their existence!)

Summary

• Matter is the fundamental material from which all physical objects are made
• Mass is a measure of how much matter an object contains.
• Volume is a measure of space
• Forces can cause attraction or repulsion between physical objects even when they are separated across a distance in space