Objects in space orbit other objects because of the gravitational force between them When the comet is far away from the Sun the gravitational force is weaker so its speed is slower When the comet is close to the Sun the gravitational force is greater so its speed is faster The closer an object is to the Sun the quicker it orbits it.

Satellites are always falling towards the Earth Because they are moving at right angles to gravity (Tangential motion) They keep in a circular path

Geo stationary satellites remain in the same position above the equator A centripetal (centre seeking) force is needed to keep objects moving in a circular path. Gravity provides this force Geo stationary satellites are used for Communications Weather forecasting They orbit every 24 hours

Some satellites orbit around the poles (Polar satellites) Their orbits are lower so they orbit the Earth more quickly The closer they are to the Earth the more quickly they orbit. Polar satellites are used for Photographing the Earth weather forecasting

ionosphere Radio waves below 30 Mhz are reflected off the ionosphere (they do not have the energy to pass through) If the waves are above 30GHz dust in the atmosphere reduces their strength over long distances

Radio waves are used for broadcasting because they diffract (spread out). This is useful when they pass a hill They also diffract around the world As diffraction happens the signal gets weaker

Diffraction happens the most when the gap is the same size as the wavelength A little diffraction at the edges Maximum diffraction

Microwaves (used in mobiles) are sent in a thin beam. They have a shorter wavelength so do not diffract much. Microwaves travel through the ionosphere to orbiting satellites, which send the signals back to Earth