This topic accounts for approximately 14% of your exam marks.
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Stable14%
F = ma, resultant forces and Hooke's Law calculations are high-frequency multi-mark questions.
Definition
Weight is the pull that a gravitational field exerts on any object that has mass
Because weight is a force, it carries a direction (always towards the centre of the planet), making weight a ; weight is measured in newtons (N)
Mass is the amount of matter in an object, a measured in kilograms (kg)
Mass and weight are not the same physical quantity even though everyday language often confuses them
The equation
W = m × g
where:
W = weight (N)
m = mass (kg)
g = (N/kg)
g on Earth is 10 N/kg (also equal to the acceleration of free fall, 10 m/s², because these two numerical values match when they describe the same physical effect from two different angles)
g varies between planets and moons: a stronger gravitational field gives a larger weight for the same mass
Mass and weight are directly proportional to one another in a given gravitational field, so doubling the mass doubles the weight
Worked example
Calculating weight and the unit mark
A satellite component has a mass of 35 kg. Calculate its weight on Earth, where g = 10 N/kg. Give the unit.