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Earth and Space - The Solar System

Grade 6IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Solar System consists of the Sun, eight planets, their moons, and smaller objects like asteroids and comets. The Sun is a star composed mainly of Hydrogen (HH) and Helium (HeHe).

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The eight planets are divided into two groups: Terrestrial planets (Mercury, Venus, Earth, Mars) which are rocky, and Gas Giants (Jupiter, Saturn, Uranus, Neptune) which are composed mostly of gases like Hydrogen (H2H_2) and Methane (CH4CH_4).

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Gravity is the force of attraction that keeps planets in orbit around the Sun. The strength of gravitational pull depends on the mass (mm) of the objects and the distance (rr) between them.

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A planet's rotation on its axis causes day and night. One full rotation is a 'day'. A planet's revolution around the Sun is one 'year'. The time taken for one revolution is the orbital period (TT).

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The Moon is a natural satellite that reflects light from the Sun. It does not produce its own light. The changing positions of the Moon relative to Earth and the Sun cause lunar phases.

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Distances in the solar system are often measured in Astronomical Units (AUAU). 1 AU1 \text{ AU} is defined as the average distance between the Earth and the Sun, approximately 1.5×108 km1.5 \times 10^8 \text{ km}.

📐Formulae

W=m×gW = m \times g

F=Gm1m2r2F = G \frac{m_1 m_2}{r^2}

1 AU≈1.5×108 km1 \text{ AU} \approx 1.5 \times 10^8 \text{ km}

Speed=DistanceTime=2πrT\text{Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{2\pi r}{T}

💡Examples

Problem 1:

An astronaut has a mass (mm) of 70 kg70 \text{ kg}. Calculate their weight (WW) on Earth, where the gravitational field strength (gg) is 9.8 N/kg9.8 \text{ N/kg}. Then, calculate their weight on the Moon, where g≈1.6 N/kgg \approx 1.6 \text{ N/kg}.

Solution:

On Earth: W=70 kg×9.8 N/kg=686 NW = 70 \text{ kg} \times 9.8 \text{ N/kg} = 686 \text{ N}. On the Moon: W=70 kg×1.6 N/kg=112 NW = 70 \text{ kg} \times 1.6 \text{ N/kg} = 112 \text{ N}.

Explanation:

Mass is a measure of the amount of matter and remains constant (70 kg70 \text{ kg}) regardless of location. Weight is the force of gravity acting on that mass and changes based on the local gravitational field strength (gg).

Problem 2:

If Jupiter is approximately 5.2 AU5.2 \text{ AU} from the Sun, calculate this distance in kilometers (kmkm).

Solution:

5.2 AU×(1.5×108 km/AU)=7.8×108 km5.2 \text{ AU} \times (1.5 \times 10^8 \text{ km/AU}) = 7.8 \times 10^8 \text{ km}.

Explanation:

To convert Astronomical Units to kilometers, multiply the value in AUAU by the standard conversion factor of 1.5×108 km1.5 \times 10^8 \text{ km}.

Problem 3:

A planet takes 365.25365.25 days to complete one orbit around the Sun. What is this time period called, and what does it represent?

Solution:

This is called the orbital period (TT) or one Earth year.

Explanation:

The orbital period is the time it takes for a celestial body to make one complete revolution (360∘360^\circ) around the object it is orbiting.

The Solar System - Revision Notes & Key Formulas | IGCSE Grade 6 Science