Weight and mass

 

Weight versus mass

Many people confuse weight and mass, but they are not the same thing. Saying ‘a bag of sugar weighs 1 kg’ is not accurate in science. Mass is the measure of how much matter an object has. The unit of mass is the kilogram (kg). Sometimes, we use grams (g) for very small masses. One kg is equal to 1000 g. Weight is the measure of how much gravity pulls on an object’s mass. The unit of weight is the newton (N).

 

 

Calculating weight and mass

The unit of mass is kilograms (kg). The unit of weight is measured in newtons (N). Different planets have different gravitational fields and therefore the value of weight changes when the object’s location changes. However, the value of mass does not change.

We use the following equation to calculate the weight of an object:

 

W = m x g

 

Where:

 

• W = Weight (N)
• m = Mass (Kg)
• g = Gravitational field strength (N/Kg)

 

For example:

 

• If someone weighs 70 kg (this is their mass).
• The gravitational strength of Earth is 10N/kg.

 

Weight (N) = Mass (Kg) x Gravitational field strength (N/Kg)

Weight = 70kg x 10N/kg

 

Weight = 700N

 

What is the difference between mass and weight?

The difference between mass and weight is as follows:

 

• Mass is how much matter something contains.
• Weight is a way of measuring the pull of gravity on an object.

 

Weight and other planets

Gravity and mass affect the weight of an object. This means that the weight of an object can change depending on how strong the gravity is where it is. Different objects in the Universe have different strengths of gravity.

The table shows how strong the gravity is on each planet:

 

Planet	Mercury	Venus	Earth	Mars	Jupiter	Saturn	Uranus	Neptune
Gravitational field strength (N/kg)	4	9	10	4	23	9	9	11

 

Summary:

 

• Many people confuse weight and mass as being the same thing.
• In science, they are very different concepts.