The Moon and inertia
The Moon has a smaller mass than the Earth. It has smaller Force per unit mass. Measured in newtons per kilogram (N/kg).. The smaller mass of the Moon will not attract a 1 kg mass with as much force as on Earth.
On the Moon, g = 1.6 N/kg.
In other words, a 1 kg mass has a weight on the Moon of 1.6 N and a 5 kg mass will weigh 8 N.
Question
a) What is the mass of a person who weighs 120 N on the Moon? (g = 1.6 N/kg)
b) What would the mass and weight of the same person be back on Earth where g = 10 N/kg?
a) m = W ÷ g
= 120 N ÷ 1.6 N/kg
= 75 kg
b) This is a trick question. The mass on Earth will be the same as you’ve calculated on the Moon = 75 kg.
The weight becomes W = m × g
= 75 kg × 10 N/kg
= 750 N
Inertia
A reluctance to move or change motion. is a resistance to a change in motion.
Look at the following diagram. If the card is pulled quickly, the coin will stay in the same place – it won’t move with the card. It will then fall into the cup.
The inertia of an object depends on its mass. More mass means more inertia. A greater resultant force will be needed to change the motion of an object with high inertia. For example, a bucket full of sand will be more difficult to push than an empty bucket.
