The Solar SystemCambridge IGCSE Physics: Flashcards

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Name the eight planets in our Solar System in order from the Sun.

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Name the eight planets in our Solar System in order from the Sun.: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
What are the four inner planets and why are they classified as rocky planets?: Mercury, Venus, Earth and Mars are the four inner planets nearest the Sun. They are rocky planets because they are small and composed primarily of rock and metal with solid surfaces.
What are the four outer planets and why are they classified as gaseous planets?: Jupiter, Saturn, Uranus and Neptune are the four outer planets furthest from the Sun. They are gaseous (or gas giant) planets because they are large and composed primarily of gases such as hydrogen and helium with no solid surface.
Explain the accretion model to account for the difference between inner and outer planets.: The accretion model explains that material rotated and formed an accretion disc around the young Sun. Gravity caused particles to collide and stick together. Inner planets formed close to the Sun where it was too hot for gases to condense, leaving only rocky material. Outer planets formed further away where lower temperatures allowed gases like hydrogen and helium to be retained by their greater gravitational pull.
What other objects besides planets exist in the Solar System?: The Solar System contains: one star (the Sun); minor planets including dwarf planets such as Pluto; asteroids; moons (natural satellites) orbiting planets; comets; and other smaller Solar System bodies.
What determines the gravitational field strength at the surface of a planet?: Gravitational field strength at the surface of a planet depends on the planet's mass. It also depends on distance from the planet - gravitational field strength decreases with increasing distance from the planet's centre.
Write the equation for calculating the time taken for light to travel a distance.: time = distance ÷ speed of light, or t = d ÷ c (where c = 3.0 × 10⁸ m/s)
Why do all planets orbit the Sun?: The Sun contains most of the mass of the Solar System. The gravitational attraction (gravitational force) of the Sun keeps planets and other objects in orbit around it.
Describe the shape of planetary orbits and the position of the Sun within them.: Planets, minor planets and comets have elliptical orbits. The Sun is not at the centre of the ellipse (except when the orbit is approximately circular, in which case the orbit is nearly circular).
How does the Sun's gravitational field strength vary with distance from the Sun?: The strength of the Sun's gravitational field decreases as distance from the Sun increases.
How does orbital speed vary with distance from the Sun?: Orbital speeds of planets decrease as distance from the Sun increases. Planets closer to the Sun orbit faster than planets further away.
Compare the speed of an object in an elliptical orbit when it is closest to the Sun versus furthest from the Sun.: An object in an elliptical orbit travels faster when it is closer to the Sun (at perihelion) and travels more slowly when it is furthest from the Sun (at aphelion).
Explain why objects travel faster when closer to the Sun using energy conservation.: Using conservation of energy: when an object is closer to the Sun, it has lower gravitational potential energy but higher kinetic energy (moving faster). When furthest from the Sun, it has higher gravitational potential energy but lower kinetic energy (moving slower). Total mechanical energy remains constant.
What planetary data can be analysed and interpreted in the Solar System?: Orbital distance, orbital duration (period), density, surface temperature, and gravitational field strength can be analysed and interpreted for planets.
Define what a dwarf planet is and give an example.: A dwarf planet is a small planetary body that has sufficient mass to be round (hydrostatic equilibrium) but has not cleared its orbital path of other debris. Pluto is the most well-known example.