Earth & The Solar System (Cambridge (CIE) IGCSE Physics)

Five objects that make up the Solar System are:

1. The Sun

2. Eight planets

3. Satellites (natural and artificial)

4. Dwarf planets

5. Asteroids and comets

The planets in order of increasing distance from the Sun are:

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

An asteroid is a small rocky object which orbits the Sun.

The asteroid belt is located between Mars and Jupiter.

Comets are made of dust and ice.

False.

Planets, dwarf planets, asteroids and comets orbit around the Sun, whereas satellites, such as moons, orbit around planets.

A natural satellite is a non-manmade object that orbits a planet, such as a moon.

An artificial satellite is a manmade object that can orbit any object in space.

The orbital radius of a planet increases with increasing distance from the Sun.

The orbital period of a planet increases with increasing distance from the Sun.

False.

The inner planets are denser than the outer planets.

True.

The surface temperature of a planet tends to decrease with distance from the Sun (with the exception of Venus).

Neptune is the furthest planet from the Sun, therefore, it is the coldest planet.

True.

Surface gravity depends on the mass of a planet.

Values of surface gravity are greater on the giant outer planets than on the small inner planets.

Therefore, the surface gravity on Saturn is greater than on Earth.

True.

The inner planets (Mercury, Venus, Earth, Mars) are small and rocky.

The outer planets (Jupiter, Saturn, Uranus, Neptune) are large and gaseous.

An accretion disc is a rotating disc of dust and gas that forms around an object, such as the Sun during its formation.

According to the accretion model:

• The inner planets are small and rocky because a small proportion of heavy elements were solid closer to the Sun

• The outer planets are large and gaseous because a large proportion of light elements were solid further from the Sun

False.

Light travels at a constant speed of 3 × 10⁸ m/s, therefore, it takes time for light to travel any distance.

The equation that can be used to calculate the time taken for light to travel a certain distance is:

It takes light 760 s or 12.6 min to travel from the Sun to Mars

• distance from the Sun to Mars = 227.9 million km

• distance from the Sun to Mars = 227.9 × 10⁶ km = 227.9 × 10⁹ m

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• 

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Gravitational field strength is the strength of the gravitational pull exerted by an object, such as a planet or moon, on another object on or near its surface.

The strength of a gravitational field around a planet depends on:

• the mass of the planet

• the distance from the planet

The greater the gravitational field strength of a planet, the greater the measured weight of a person standing on its surface.

Therefore, your weight would be the greatest on Jupiter, as this is the largest (most massive) planet.

The greater the mass of a planet, the greater the strength of the gravitational field at its surface.

As the distance from a planet increases, the strength of the gravitational field decreases.

True.

Gravitational field strength is constant at the surface of a given planet, but it decreases with distance above the planet's surface.

The gravitational force exerted on an orbiting body acts towards the centre of the larger body it is orbiting.

False.

The strength of the Sun's gravitational field decreases as the distance from the Sun increases.

The orbital speed of a planet decreases as the distance from the Sun increases.

Orbital speed is the average speed of an object as it orbits around a larger object.

True.

When a planet orbits the Sun or a satellite orbits a planet, they move in approximately circular paths.

The equation for calculating orbital speed is

Orbital period is the time it takes an object to complete one full orbit around another object.

The orbital period of the Earth is 365 days, the time it takes to complete one orbit around the Sun.

False.

The orbital radius is always taken from the centre of mass of the orbiting body.

The distance travelled by an object moving in circular motion is equal to the circumference of the orbit = , where r is the radius of the orbit.

True.

An object in a circular orbit has a constant orbital radius.

The equation for orbital speed is

Where:

• = orbital speed, measured in m/s

• = orbital radius, measured in m

• = orbital period, measured in s

True.

The orbital radius of a satellite orbiting the Earth is

Where:

• = orbital radius of the satellite, measured in m

• = radius of the Earth, measured in m

• = height above the Earth's surface, measured in m

True.

The orbits of planets, minor planets and comets are elliptical.

Comets have the most elongated elliptical orbits in the Solar System.

False.

When a body moves in a circular orbit, the larger body will be at the centre of the circle.

When a body moves in an elliptical orbit, the larger body will be at one of the two foci of the ellipse.

Therefore, the Sun is not at the centre of an elliptical orbit.

As a comet approaches the Sun it speeds up.

In terms of conservation of energy, when a comet approaches the Sun, it gains kinetic energy and loses gravitational potential energy. This causes it to speed up.