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Science

Weight and friction

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Gravity is a force that attracts objects with mass towards each other. The weight of an object is the force acting on it due to gravity. The gravitational field strength of the Earth is 10 N/kg.

The stopping distance of a car depends on two things: the thinking distance and the braking distance.

Weight

Weight is not the same as mass. Mass is a measure of how much stuff is in an object. Weight is a force acting on that stuff.

You have to be careful. In physics, the term weight has a specific meaning, and is measured in newtons. Mass is measured in kilograms. The mass of a given object is the same everywhere, but its weight can change.

Gravitational field strength

Weight is the result of gravity. The gravitational field strength of the Earth is 10 N/kg (ten newtons per kilogram). This means an object with a mass of 1kg would be attracted towards the centre of the Earth by a force of 10N. We feel forces like this as weight.

You would weigh less on the Moon because the gravitational field strength of the Moon is one-sixth of that of the Earth. But note that your mass would stay the same.

Weight

On Earth, if you drop an object it accelerates towards the centre of the planet. You can calculate the weight of an object using this equation:

weight (N) = mass (kg) × gravitational field strength (N/kg)

Question

A person has a mass of 60kg. How much do they weigh on Earth, if the gravitational field strength is 10N/kg?

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Answer
  • weight = mass × gravitational field strength
  • weight = 60kg × 10N/kg
  • weight = 600N
Question

How much would the same person weigh on the Moon, if the gravitational field strength is 1.6N/kg?

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Answer
  • weight = mass × gravitational field strength
  • weight = 60kg × 1.6 N/kg
  • weight = 96N

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