Weight, Mass, Gravity

What is gravity?

A force of attraction between all masses.

When do you usually notice gravity?

When at least one of the masses is very large, like a planet.

What are the two effects of gravity on a planet's surface?

It makes all things fall towards the ground and gives everything a weight.

What is mass?

The amount of 'stuff' in an object; it stays the same everywhere in the universe.

What is weight?

The force acting on an object due to gravity.

What causes weight on Earth?

The gravitational field around Earth.

What does gravitational field strength depend on?

Location — it's stronger the closer you are to the mass and stronger for larger masses.

Does weight change with location?

Yes — it depends on the local gravitational field strength.

Why does a 1 kg mass weigh less on the Moon than on Earth?

Because the gravitational field strength on the Moon is weaker (1.6 N/kg vs 9.8 N/kg).

What unit is weight measured in?

Newtons (N).

How is weight measured?

Using a calibrated spring balance or newtonmeter.

What is the centre of mass?

The point where the mass of an object is concentrated and acts.

What is the difference between mass and weight?

Mass is a scalar measured in kg; weight is a force measured in newtons and depends on gravity.

What is the equation for weight?

Weight = Mass × Gravitational Field Strength (W = m × g).

What is the gravitational field strength on Earth?

Approximately 9.8 N/kg.

How are mass and weight related?

They are directly proportional — double the mass, and the weight doubles.