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The Solar System and orbits
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Gravity holds the Solar System together. Our ideas about it have changed over centuries. Separate Physics only.
The Solar System
The Sun, eight planets, dwarf planets such as Pluto, moons, asteroids and comets.
Models changed from the geocentric (Earth at the centre) to the heliocentric (Sun at the centre), supported by Galileo's observations of Jupiter's moons.
Models changed from the geocentric (Earth at the centre) to the heliocentric (Sun at the centre), supported by Galileo's observations of Jupiter's moons.
Orbits
Gravity provides the force that keeps planets, moons and satellites in orbit.
In a circular orbit the speed is constant but the velocity changes because the direction changes.
Smaller orbits need a higher speed.
In a circular orbit the speed is constant but the velocity changes because the direction changes.
Smaller orbits need a higher speed.
Weight on other planets
weight = mass × gravitational field strength
On the Moon, g is about 1.6 N/kg; on Earth about 10 N/kg. Mass stays the same.
On the Moon, g is about 1.6 N/kg; on Earth about 10 N/kg. Mass stays the same.
An astronaut has mass 80 kg. Find their weight on the Moon (g = 1.6 N/kg).
- W = 80 × 1.6
Answer: 128 N
The heliocentric model replaced the geocentric one. Gravity provides the force for orbits; velocity changes even at constant speed. Weight = mass × g, which varies between planets.
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