Geostationary satellites take 24 hours to orbit the earth, above the equator.
This means they always stay above the same point on earth
A gravitational force keeps a satellite in orbit
The height and period of a satellited orbit depends on its job
Any object moving in a circle needs a force towards the centre of the circle to maintain its circular path
This is called centripetal force
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SATELLITE COMMUNICATION
Some radio waves are reflected by the ionosphere
High frequency radio waves (microwaves) pass through it to reach an orbiting satellite
Long wavelength radio waves are easily diffracted around hills
Short wavelength microwaves only diffract a small amount
The amount of diffraction depends on the size of the gap or obstacle
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SCALES & VECTORS
A scalar quantity (e.g. speed) has size only
A vector quantity (e.g. velocity) has size and direction
momentum = mass x velocity
Momentum is a vector which is always conserved
Changes in temperature and volume cause changes in pressure
Rate of change of momentum creates a force on the walls of the container
Rockets expell a large number of particles at high speed
Projectiles : 1) have a constant horizontal velocity. 2) have a trajectory that is parabolic. 3) accelerate towards the ground at 10 m/s2
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WAVES
Light travels in straight lines
Diffraction and interference of light can only be explained by a wave model
Polarised light has oscillations in one plane only
A convex lens makes a beam of light converge
Convex lenses are used in cameras and projectors to produce real, inverted images and as a magnifying glass to produce a virtual image that is the right way up
Magnification = image size / object size
Interference occurs when two waves overlap. They can reinforce or cancel
This results in louder and quiter areas in sound and bright and dark areas in light
The type of interference depends on the path difference between the two waves
Refraction occurs whn light passes from one medium to another.
As the speed of light changes, its direction can change
refractive index = speed of light in a vacuum / speed of light in a medium
Light sometime produces a rainbow, or spectrum of colours - dispersion
Total internal reflection occurs when light goes from a dense to a less dense medium.
The critical angle is the angle of incidence for which the angle of refraction is 90'
At greater angles of incidence all the light is totally internally reflected
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