Gravity: Calculate Mass and Weight

Use kilograms for mass and newtons for gravitational force.

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Weight W = m x g. Mass m is measured in kilograms; local field strength g can be measured in newtons per kilogram. Weight is measured in newtons. Moving an unchanged object to another world does not change its mass.

Worked example

For a 3 kg package, g = 10 N/kg gives W = 30 N. On the Moon, using g = 1.6 N/kg gives W = 4.8 N. These are rounded teaching values; the mass remains 3 kg.

A 3 kilogram object weighs about 30 newtons using Earth's approximate field strength of 10 newtons per kilogram, and about 4.8 newtons using the Moon's 1.6 newtons per kilogram.

Would you believe it?

A floating object in an orbiting spacecraft still has mass. Floating does not remove its resistance to a change in motion.

NASA: mass and weight

Question 1 At g = 10 N/kg, what is the weight of a 2 kg object? 20 N 20 kg 2 N

Question 2 At g = 1.6 N/kg, what is the weight of a 5 kg object? 50 N 5 N 8 N

Question 3 An unchanged 4 kg object moves from Earth to the Moon. Its mass is what? Zero 4 kg 4 N

Question 4 Which unit measures weight as a force? Newton Kilogram Second

Question 5 A 6 kg object weighs 30 N. What is local g? 180 N/kg 0.2 kg/N 5 N/kg

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