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Mass, Weight, Density and Pressure

Quick questions on Mass, weight and gravitational field strength: N(A)-Level Physics

3short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is mass?
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Mass is the amount of matter in an object. It is measured in kilograms (kg\text{kg}). Mass does not change when you move the object: a 3 kg3\ \text{kg} bag has a mass of 3 kg3\ \text{kg} on Earth, on the Moon, or floating in space. Mass is a scalar.
What is weight?
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Weight is the force on an object due to gravity. Because it is a force, it is measured in newtons (N\text{N}) and it is a vector that always points downward, toward the centre of the planet.
What is gravitational field strength?
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The gravitational field strength, gg, is the gravitational force on each kilogram of mass. On Earth it is about 10 N kg−110\ \text{N kg}^{-1} (more precisely 9.81 N kg−19.81\ \text{N kg}^{-1}, but 1010 is used for simple work). On the Moon it is only about 1.6 N kg−11.6\ \text{N kg}^{-1}.

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