BAB 6 : KINETICS OF PARTICLES

What is Mass?

If an object takes up space and has mass, then it is said to be made of matter. Everything around you, including you, is made from matter. Matter is made from atoms, different materials (elements) have different atoms, that is what makes them different.

Mass is a measurement of all the matter within an object, and we measure mass with the unit of measurement called the gram, but since one gram is so small, it is more common to measure mass with kilograms (kg).

The mass of an object will remain the same anywhere in the universe, unless some material is removed, regardless of acceleration or change in shape, therefore it is a fundamental property of that object.

A swimming pool of water contains more matter than a bucket of water, therefore it has more mass.

What is Weight?

Weight is actually measured in Newtons (N) because it is a measurement of force. Weight measures how much gravity is trying pull an object towards the centre of the earth. The weight of an object will change throughout the universe, since the forces of gravity change.

Weight can be calculated with the following equation:

Weight = Mass x Gravity

If an objects mass remains constant, then the only variable in the equation is gravity. Gravity varies between planets, on earth it is 9.81m/s2 but on the moon it is around 1/6 of this at 1.64m/s2.

Example

Mass of object = 10kgGravity = 9.81m/s2

Weight = 10kg x 9.81m/s2

Answer: 98.1N

How does weight change?

The mass of an object (e.g. a 10kg box) stays the same whether it is on Earth, the Moon or in space. But the weight of an object will vary. As we have already calculated, the 10kg box will weigh 98.1N on Earth, but on the moon it will weigh just 16N (around 1.6kg) because the gravitational pull of the Moon is much less than the Earth. In space, away from any gravitational pull, the mass will still be 10kg but the box will have no weight because the mass is not being pulled by gravity.

Summary

• Gravity causes weight
• Weight is measured in Newtons (N)
• Mass is measured in Kilograms (kg)
• Weight changes depending on gravity
• Mass remains the same regardless of gravity