P5a - Satellites, gravity and comets

P5a - Satellites, gravity and comets

1. Satellites

   • Geostationary satellites are used for communications and stay in a fixed position above the Earth's surface
   • Low polar orbit satelites are closer to the ground, and are used for weather forcasting and imaging the Earth
   • A satellite is an object that orbits a large object in space
   • The Earth has many artificial satellites in orbit around it. These have been built by people and launched into orbit using rockects.
   • Satellites in lower orbits travel faster than those in higher orbits. The higher the orbit of a satelite, the longer it's 'period'.
   • 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.
   • 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.
   • 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.
   • 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
   • 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.
   • 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,

2. Planets and Comets

   • 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.
   • 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,
   • 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,

3. Gravity

   • 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.
   • 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.
   • Gravity is the universal force of attaction between masses. The greater the mass involved, the greater the force.
   • 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.
   • mass/moles x molar mass