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Earth and Space - The Solar System and gravity in space

Grade 5IGCSE

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 other objects like asteroids and comets. The planets in order from the Sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

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Gravity is a non-contact force of attraction that pulls objects toward each other. The more mass an object has, the stronger its gravitational pull.

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The Sun's massive gravity keeps the planets in their paths, known as orbits. Without gravity, planets would fly off into space in a straight line.

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Mass is the amount of matter in an object and is measured in kilograms (kgkg). It does not change regardless of where you are in the universe.

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Weight is the force of gravity acting on an object's mass and is measured in Newtons (NN). Weight changes depending on the gravitational field strength (gg) of the planet or moon you are on.

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The Earth rotates on its axis once every 2424 hours (causing day and night) and orbits the Sun once every 365.25365.25 days (one year).

📐Formulae

W=mimesgW = m imes g

gEarth≈10 N/kgg_{\text{Earth}} \approx 10 \text{ N/kg}

gMoon≈1.6 N/kgg_{\text{Moon}} \approx 1.6 \text{ N/kg}

💡Examples

Problem 1:

An explorer has a mass of 50 kg50 \text{ kg} on Earth. Calculate their weight on Earth where the gravitational field strength is 10 N/kg10 \text{ N/kg}.

Solution:

W=50 kg×10 N/kg=500 NW = 50 \text{ kg} \times 10 \text{ N/kg} = 500 \text{ N}

Explanation:

Weight is found by multiplying the mass by the gravity of the planet. Even though the explorer's mass is 50 kg50 \text{ kg}, the force they exert on the ground is 500 Newtons500 \text{ Newtons}.

Problem 2:

If the same explorer (50 kg50 \text{ kg}) travels to the Moon, what will be their mass and their approximate weight? (Assume gMoon=1.6 N/kgg_{\text{Moon}} = 1.6 \text{ N/kg})

Solution:

Mass = 50 kg50 \text{ kg}; Weight = 50 kg×1.6 N/kg=80 N50 \text{ kg} \times 1.6 \text{ N/kg} = 80 \text{ N}

Explanation:

Mass remains the same (50 kg50 \text{ kg}) because the amount of matter in the explorer hasn't changed. However, the weight is much lower (80 N80 \text{ N}) because the Moon has less gravity than Earth.

Problem 3:

What two factors determine the strength of the gravitational pull between two objects?

Solution:

  1. Mass of the objects. 2. Distance between the objects.

Explanation:

According to the laws of physics, gravity increases if the objects are more massive or if they are closer together.