Difference Between Body Mass and Body Weight

Mass and weight are two different concepts which are loosely used to refer to the same thing in lay terms. In scientific context, they are not as related as many seem to think.

Body Mass

Mass means the actual amount of matter an object contains. Mass remains constant wherever the object is. Inertia is a better way to explain the concept of mass. A hot air balloon, which floats in the air, has no weight, but the matter it contains is the same. It is still difficult to initiate movement of it by an external force because of the large amount of matter it contains. Inertia is the resistance an object shows to change its current state of motion (moving or staying still) when an external force is exerted on it. Here is an example that explains the concept of mass and inertia. An adult who has a larger mass compared to a boy will take a stronger push to swing forward. Therefore, the inertia or resistance is high. A small child will swing much more if the same force is applied due to smaller resistance or inertia. A set of balance scales will have gravity acting on both trays and thus it gets cancelled out. Only the mass is compared in a balance scale. A balance scale would work the same on the moon and on earth. Thus, the body mass refers to the amount of tissue it contains. Mass of an athlete will be higher than one who is not an athlete.

Body Weight

The weight is the actual force an object experiences because of the action of gravity on it. This is why people weigh a lot less in space. A ship, which floats on water, has a great mass, and it would take a huge engine to make it move. That is because of its inertia. However, the ship floats on water as if it is weightless. This is because the weight, the actual force pushing the ship down, is counteracted by the buoyancy generated by the large volume of water it displaces. An object, which floats in a basin of water, will appear weightless. If the whole contraption is placed on a scale, the object will seem to weigh the same because it transmits the weight down to the scale through the bottom of the water basin. The gravity is a major factor in weight. The weight of an object will be less underwater, on the moon, and in space while it will be more on Saturn. This is because of the net force it experiences due to gravity. The unit used to measure weight is Newton. Mass multiplied by the gravitational force converts mass to weight.

Body weight refers to the actual force the body experiences due to gravity. Astronauts who spend a long time floating in space tend to get disuse atrophy of leg muscle because they bear less weight while in space. We can jump a lot easier in water than on dry land because of the buoyancy counteracting the force generated by gravity.

What is the difference between Body Mass and Body Weight?

• Mass refers to the actual amount of matter in an object.

• Weight refers to the force exerted on an object by the gravity.