# P5 - Space for Reflection

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## Orbits

low polar orbit - an orbit that goes directly over the poles

low earth orbit - satalites used for a close up veiw of earth

Geo stationary orbit - circles the earth at the same rate the earth is spinning, making it look still.

• gravitational forces are proportional to 1 over distance squared
• a centripetal force is needed to keep an object moving in a circle, the closer an object is to earth the faster its orbit
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## SUVAT equation

----- given on page 2 equation list

• t = time (s)
• s = displacement (m)
• u = intital velocity (m/s)
• v = final velocity (m/s)
• a = acceleration (m/s2) or gravity if object is falling = 10
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## Scalars & Vectors

Scalars - tell you how big something is -- magnitude only, examples; temeratures, speed, distance, mass

Vectors - have magnitude & a direction, examples; force, velocity, displacement

this means you can use pythagoras or trigonometry (if an angle is given) to find total velocity

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## Projectiles

• The trajectory of a projectile is parabolic (a curved path)
• for a projectile question you should draw a SUVAT table

Horizontal                 Verticle

S

U

V

A

T

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## Electromagnetic Waves & Satellites

electromagnetic waves that can pass through the atmosphere:

• microwaves
• visible light
• ultraviolet
• a signal is sent up to the satalite, where it is processed & retransmitted back to earth to another reciever. multiple Stalalites mean signals can travel further
• Due to microwaves having a shorter wavelength than radiowaves, they dont diffract as much, so dishs must be placed in straight lines as this is how microwaves travel.
• The size of the gap affects the diffraction of waves. If the gap is the same size as the wave length, then diffraction is at it's greatest.

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## Interference

• If two sound waves reinforce eachother to make a stronger sound, or they will cancel eachother out.

• If there is an even number of path difference, then the wave will constructive interfere.
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## Light... Particle or Wave?

evidence for light as a particle:

• travels in staright lines
• doesn't spread out (diffract), if it did shadows would be blurry (solar eclipse)

evidence light is a wave:

• light can be polarised proving its a transerse wave
• light can be defracted with a really short gap, due to it's short wavelength
• light can form an intereference pattern

polarisation- transverse waves can be plane polarisied meaning they are limmitted to one plane of ossilation instead of many. A polariod filter lets through light that is polarised in a certian plane.

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## Experiment to Show Interference

(past exam question)

• A transverse wave must be used, so you could use a ripple tank
• therfore wou will need two dippers in a water tank that produce waves of the same frequency
• you will get constructive & destructive interference
• when peaks and throughs meet constructive intereference occurs
• when waves meet and are not 'in phase' then destructive interference occurs

you may be asked to draw a diagram:

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## convex lenses & magnification

• magnification - where an image is magnified (appearing larger than the actual object)
• for an object to be magnified it must be between F (focal point) and 2F
• an object closer or less than F , then light defracts and no image is made
• a real image can be projected but a virtual image cannot
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## Momentum

momentum - a product of mass and velocity (momentum = mass x velocity)

V= M1 U1 + M2 U2 / M1 + M2

• when a cricketer hits a ball, the action is the hit, the reaction is the ball flying forward and the bat flying backwards
• when hit the ball changes velocity as the force applied changes its momentum.
• a gun recoils beacuse it put a force on the bullet, while the bullet exerts a force on the gun, which is equal and opposite to the original force, causing the gun to recoil
• total momentum before collision = total momentum after collision -- due to the law of conservation of mass, however this only applies if no other force is acting up the objects (i.e. friction)
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