P5a - Satellites, gravity and comets

Satellites
1. Geostationary satellites are used for communications and stay in a fixed position above the Earth's surface
2. Low polar orbit satelites are closer to the ground, and are used for weather forcasting and imaging the Earth
3. A satellite is an object that orbits a large object in space
4. The Earth has many artificial satellites in orbit around it. These have been built by people and launched into orbit using rockects.
5. Satellites in lower orbits travel faster than those in higher orbits. The higher the orbit of a satelite, the longer it's 'period'.
6. Satellites in low polar orbit pass over the poles. They orbit between 110km and 200km above the Earth's surface, taking around 90 minutes to make each orbit.
7. Geostationary satellites have a different path to polar satellites - they are in orbit above the equator. The height of thier orbit - 36,000km - is just the right distance so that it takes them 24 hours to make each orbit.
8. Artificial satellites are continually accelerating towards the Earth. This is because of the gravitational force of attraction between the satellite and the Earth. If a satellite stopped moving forwards, the Earth's gravitational pull would make it fall to Earth.
9. The forward speed, or tangential motion, of a satellite must be just right to keep the satellite in orbit: If the tangential motion is too slow, the satellite will fall to Earth, if the tangetial motion is too fast, the satellite will travel into space
10. Low polar orbit is close to the ground, so the gravitational attraction is strong. This produces a high centripetal acceleration, so the tangential speed must be high.
11. A geostationary satellite if further from the ground, so the gravitational attraction is weaker. This produces a lower centripetal acceleration, so th tangential speed must be less,
Planets and Comets
1. The force of gravity between two objects decreases as the objects move further apart. It follows an inverse square law - the force between two objects is invesley proportional to the distance between the squared.
2. The orbital peiod of a planet depends upon its distance from the sun. The further a planet is from the sun, the longer its orbital period. This is because the further away a planet is the further it has to travel in orbit ans the weaker the gravitaional force of attraction between it and the Sun,
3. A periodic comet has a highly elliptical orbit (oval-shaped, rather than circular) . When a comet comes close to the Sun, the gravitational force of attraction is high and it travels quickly. When a comet travels far from the Sun, the gravitational force of attraction is less and it travels more slowly,
Gravity
1. A moving object will continue to move in a straight line at the same speed unless a force acts on it. For and object to move in a circle, a force has to act on it all the time. This force is called the centripetal force.
2. The centripetal force acts toward the centre of the circle. Gravity id the centripetal force that keeps planets moving around the Sun, and satellites moving around planets.
3. Gravity is the universal force of attaction between masses. The greater the mass involved, the greater the force.
4. The force of gravity between two objects with small masses like a table and a chair is small because the objects are. However, large objects like planets have a much greater mass and so have a much greater gravitational force.
5. mass/moles x molar mass

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P5a - Satellites, gravity and comets

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