Outside of the world of physics ‘weight’ is a generic term used to refer to an object’s mass – the amount of matter an object has, directly dictated by its amount of and type of atoms – and its weight, the force created when a mass is acted upon by a gravitational field. This is because most masses on Earth have weight and the relationship between the two factors is directly proportional – ie, the more massive an object is, the greater its weight.

However, in the world of physics – which deals with objects of infinite mass under wildly varying forces, not just the relatively stable force of Earth’s gravity – mass and weight are distinct. To understand the distinction fully between mass and weight it is important to understand their fundamental principles.

Newton’s law of universal gravitation states that every massive particle in the universe attracts every other massive particle to some extent, and considering the size of Earth it has a pretty big pull. On Earth this resultant force is gravity (g) and its average numerical value is 9.81m/s2 – meaning that, ignoring air resistance, the speed of an object falling freely near the Earth’s surface increases by about 9.81 metres per second every second. However, gravity pulls down on both airborne and ground-based objects and this force acting upon a mass is an object’s weight.

For example, an apple has a mass of roughly 100 grams and on Earth that apple is pulled down by gravity at 9.81m/s2 , or roughly by the force of one newton (a newton is a unit of measurement equal to the amount of net force required to accelerate a mass of 100 grams at a rate of one metre per second per second). This means that the apple has a weight of one newton, but a mass of 100 grams. Equally, the average human weight in newtons is 700, while their average mass is 70kg. The human’s / apple’s weight is therefore the force of gravity acting upon their mass, while their mass is purely the amount of matter they are made up from.

In physics, however, there are objects that are not affected by Earth’s gravity, of varying atomic density and with a mass to weight ratio that is not directly proportional, hence the distinction.