IGCSE Physics Specification

Edexcel 4PH1

Section 8: (b) Motion in the universe

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#8.2

know that:

- the universe is a large collection of billions of galaxies
- a galaxy is a large collection of billions of stars
- our solar system is in the Milky Way galaxy.

#8.3

understand why gravitational field strength, g, varies and know that it is different on other planets and the Moon from that on the Earth

#8.4

explain that gravitational force:

- causes moons to orbit planets
- causes the planets to orbit the Sun
- causes artificial satellites to orbit the Earth
- causes comets to orbit the Sun.

#8.5

describe the differences in the orbits of comets, moons and planets

#8.6

use the relationship between orbital speed, orbital radius and time period:

\(\text{orbital speed} = \dfrac{\text{2 × π × \text{orbital radius}}}{\text{time period}}\)

\(v = \dfrac{2 × π × r}{T}\)