Mass, weight and gravitational field strength
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 8 practice questions, 1 real past-paper question with the answer explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Astronauts on the Moon
- Mass
- Weight
- Mass or weight?
Read the transcript of the teaching part
Last time
Before we start: last time, in Speed, velocity and acceleration, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Astronauts on the Moon
On the Moon, an astronaut can jump much higher than on Earth. Did he lose some of himself? No. His mass is exactly the same. What changed is his weight, because the Moon pulls less strongly.
Mass
Mass is the amount of matter in an object. It is measured in kilograms. Mass is a scalar, and it does not change when the object moves to a different place. Mass also resists a change in motion: the more mass, the harder it is to start or stop. We measure mass with a balance, by comparing the object with known masses.
Weight
Weight is the force of gravity on an object. It is a force, so it is measured in newtons. Weight is a vector, and it always points downwards, towards the centre of the Earth. Weight depends on the strength of gravity where you are. We measure weight with a newtonmeter, which is a spring balance.
Mass or weight?
Put the two side by side. Mass is in kilograms, measured on a balance, a scalar, and the same everywhere. Weight is in newtons, measured on a newtonmeter, a vector, and it changes with gravity.
How often it comes up
The whole chapter: Mass and Weight, Mass and Weight.
Chapter 1.3: Mass, weight and density
- Mass, weight and gravitational field strength 5 min
- Density and how to measure it 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.