The mass of an object is the amount of matter or "stuff" it contains. The more matter an object contains, the greater its mass. An elephant contains more matter than a mouse, so it has a greater mass. Mass is measured in kilograms or kg, but it is often easier to measure mass in grams or g. A 100 kg object has a greater mass than a 5 kg object. An object's mass stays the same wherever it is.
Gravity
All objects have a force that attracts them towards each other. This is called gravity. Even you attract other objects to you because of gravity. But you have too little mass for the force to be very strong. Gravity only becomes noticeable when there is a really massive object like a moon, planet or star.
Gravitational force increases when:
the masses of the objects involved increases
the distance between the objects decreases
The Earth has more mass than the Moon, so the gravitational force is greater on the Earth than it is on the Moon. The gravitational force is greater on the Earth's surface than it is in space, high above the Earth. The Earth's gravitational force pulls objects towards the centre of the Earth.
"Down" is towards the centre of the Earth, wherever you are on the planet
