Mass

Mass is a scientific measure of the amount of matter an object is made up of. No matter where you are at given moment in time, mass is constant. So, whether you're walking to the shop to stock up on groceries or bouncing around on the moon, your mass is the same. Obviously, if you're on a diet that's not the answer you want to hear but don't panic - we'll get to the all-important definition of weight shortly.

Some other key points about mass

Fact file on the prototype one kilogram measure, a platinum-iridium alloy block housed since the 1880s under lock-and-key at the International Bureau of Weights and Measures in Sevres, France.

Standard of Mass:

This mass standard was established in 1887 and has not been changed since that time because platinum iridium is an unusually stable alloy. A duplicate of the Sevres cylinder is kept at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland.

Some key points about weight

What Is The Difference Between Mass And Weight?

Weight is a form of measurement that is dependent on gravity and, unlike mass, your weight can vary depending on where you are in the universe. But how can weight vary whilst mass has to remain constant? It's fairly simple: weight is a variable i.e. it can change based on the amount of gravitational pull an object exerts on a body. Scientists have defined weight using this equation: $$w=mg$$ where $w$ is weight, $m$ is Mass and $g$ is Gravitational Acceleration.

Mass and weight example - the moon

In the below example, we've featured an astronaut on earth and on the moon. The Moon's gravity is much less than the Earth's gravity - approximately one sixth. So, a 100 kg astronaut weighs 980N on Earth. On the Moon, the astronaut would weigh only 162.2N. However, the astronaut's mass is 100kg where-ever they are.

Weight on Earth: $ 100kg \times 9.8m/s^2 = 980N.$

Weight on Moon: $100kg \times 1.622 m/s^2 = 162.2N.$