The Physics PHYA2 thread! 5th June 2013

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Forces acting on an object in equilibrium form a closed loop (Vector triangle)

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Define moment: force x perpendicular distance, and is the turning effect of a force around a turning point.

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Principle of moment: For a body to be in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point.

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Torque = Force (Turning force) x perpendicular distance between them.

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gives the gradient on a curve to be velocity. and since is acceleration, therefore the stepper the curve the greater the acceleration.

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Newton's First Law: An object will stay at rest or in uniform velocity, unless a resultant foce acts on it.

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Newton's Second Law: Acceleration is proportional to the resultant foce acting on it at a certain mass. F=ma

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Newton's Third Law: When 2 objects interact, they exert an equal and opposite force on eachother.

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Free fall is when the only force acting on an object is gravity.

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For projectile motion: VERTICAL you use SUVAT, for HORIZONTAL you use and in both cases 't' is the same.

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When Friction force = Driving Force object stops accelerating and reaches its terminal velocity.

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Types of friction: Contact (Friction), Fluid (Drag, Air resistance, Fluid Resistance)

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Principle of conservation of energy: Energy cannot be created or destroyed, but can be transferred from one form to another.

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Hooke's Law: Extension is proportional to force given it is within the limit of proportionality.

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Experiment to investigate extension:

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Elastic and Plastic deformation: If elastic, material will return to original length. Plastic when material will not return to original length

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Young Modulus:

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Young's Experiment:

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Waves are vibrations, they only carry and transfer energy.

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4 things a wave can do:

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Phase difference: Amount by which one wave lags behind another wave.

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Transverse waves: Vibrations oscillating at right angles to the direction of travel (Electromagnetic waves, waves on rope, ripple of water ...etc)

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Longitudinal waves: Vibrations oscillating along direction of travel (sound)

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Application of polarisation: Glare reduction (polaroid sunglasses). Improving TV and radio signals by lining up the rods of the receiving aerial to the transmitting aerial.

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Optical fibres: light in optical fibres is used to transmit phone and cable TV signals. Light doesn't heat up fibre therefore little energy loss. No electrical interference. and it is a cheaper alternative.

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Signal loss (reduction in amplitude) in optical fibres are caused by energy lost through absorption and scattering.

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Signal broadening is caused by multi-path dispersion which is when the signal travels straight down the middle and arrives earlier than those undergoing T.I.R.

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Principle of Superposition: When 2 or more waves cross, the resultant displacement equals the vector sum of the individual displacement.

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Constructive interference: when displacement combine to make an even bigger one (e.g. crest plus crest)

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Destructive interference: when negative and positive displacement combine to cancel out (e.g. crest plus trough)

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Stationary or standing wave: is the superposition of two progressive waves with the same frequency and amplitude travelling in opposite directions towards each other. this is when you get fundamental frequency which is . if you double the fundamental frequency you get the second harmonic (first overtone). Triple the fundamental you get third harmonic (second overtone) and so on ...

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Fundamental frequency depends on the length, mass and tension of a spring.

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Application of stationary waves: Microwaves, sound waves.

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you get greatest diffraction if the slit size is equal to

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Laser is monochromatic (has a single wavelength) and coherent (same frequency and constant phase difference).

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laser beams are powerful and can cause damage to eyesight, this can be prevented by wearing safety laser goggles or removing any reflective surfaces.

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Path Difference: how much further a wave has travelled than the other wave.

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When you get constructive interference, at your first order(s) [bright fringes] your path difference is where is an integer this also means that the phase difference is a multiple of .

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where you get [dark fringes] between say zero and the first order or first and second order, the path difference is where the phase difference is a multiple of (for it to be perfectly out of phase).

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non - coherent light such as white light will have wider maxima containing different colours with central white fringe. light is continuous range of frequencies

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Young's double slit experiment: . w is fringe spacing. is wavelength, s is spacing between slits, and D is distance from slits to screen.

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Diffraction grating: They have more slits causing bright bands to be brighter and narrower and dark fringes to be even darker. monochromatic light is used causing interference patterns to be sharper and more accurate of a measurement.