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

(http://chubbyrevision-a2level.weebly.com/uploads/1/0/5/8/10584247/902267042_orig.png?203)----- 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(http://2.bp.blogspot.com/_251m7Pgu_hc/TJ65iEOFUbI/AAAAAAAAABI/dsbwFotPb-o/s1600/vector+triangle.png)

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:

  • radio waves
  • microwaves
  • infrared radiation
  • 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.

(http://electron6.phys.utk.edu/light/images4-6/inter1.gif)

  • 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:

(http://cronodon.com/images/Single_slit_diffraction_2b.jpg)

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convex lenses & magnification

(http://www.passmyexams.co.uk/GCSE/physics/images/convex_lens.jpg)(http://www.passmyexams.co.uk/GCSE/physics/images/equation_magnify.jpg)

  • 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)

(http://www.passmyexams.co.uk/GCSE/physics/images/momentum_4.jpg)  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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