Gravitational fields, orbits and planetary data
Watch the whole lecture free
Make a free account to watch every lecture to the end: 1 worked example, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
That was the teaching part. The rest of this lecture is free with an account: 1 worked example, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
No password needed now: we email you a link to set one. Already have an account? Sign in, then come back to this page.
The teaching part (1 min) is free to watch. A free account opens the whole lecture: 1 worked example, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Falling, but missing the ground
- Gravitational field
- Weight and g
Read the transcript of the teaching part
Last time
Before we start: last time, in Decay equations and half-life, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Falling, but missing the ground
An orbiting satellite is falling all the time. It is moving sideways so fast that as it falls, the Earth curves away beneath it. It never hits the ground. The same force that makes an apple fall also holds the Moon, the planets and the satellites in their orbits.
Gravitational field
A gravitational field is a region where a mass experiences a force because of another mass. The force is always attractive. The bigger the masses, the bigger the force. The greater the distance, the weaker the force. Near a planet, the field strength g is the force on each kilogram, in newtons per kilogram.
Weight and g
The weight of an object is the gravitational force on it. W equals m g. On the Earth, g is about 10 newtons per kilogram. On the Moon, it is 1.6. On Jupiter, about 25. The mass does not change, but the weight does. A 60 kilogram person weighs 600 newtons on the Earth, and 96 newtons on the Moon.
6.1–6.2 Earth, stars and the Universe
- Gravitational fields, orbits and planetary data 6 min
- Galaxies, light-years and redshift 5 min
- The Sun and the life cycle of a star 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.