Speed: ms -2 Acceleration: ms Distance: m Time: s Mass: kg Force: N Energy: J Power: W Current: A Resistance: Voltage: V
acceleration, ie. a collision will have the same
Centripetal Motion
impulse regardless of the presence of padding Sources of centripetal force:
Ω
Tension, eg: Gravity o Along a string o
Sideways frictional forces
Newton's Laws 1. Every object continues in a state of rest or constant velocity unless acted on by an unbalanced force. 2. The rate of change of momentum is directly proportional to the magnitude of the net force and is in the direction of the net force. 3. For every action there is an equal and opposite reaction. Action-reaction Action-reaction forces act on different objects , e.g.. Joe and and wall Newton's laws assume that space and time are absolute, in contrast with Einstein, who proposed that space and time are relative. The inertial frame of reference refers to objects moving at a constant speed, where Newton’s laws work (ie. the third law wouldn’t work if Joe broke the wall down).
Acceleration is independent of mass Force acts equally on both bodies Velocity is directed at a tangent to the path
−
−
a F v M m r T
Inelastic:
gravitational field strength (N Kg 1 ) 2 acceleration ( ) Force (N) velocity (M s 1 ) Central mass (kg) Orbiting mass (kg) radius or orbit (m) period of orbit (s)
Action/reaction forces: Always exist in pairs Are equal in magnitude Act in opposite directions Act on separate objects
n o i t c a e R / n o i t c A
This value is a constant for bodies orbiting the same central mass
=
4
1
2
=
2
2
2
=
2
3
2
2
=
2
Physics Unit 3 Cheat Sheet (E/P and M/S) Transistor Amplifier
Phototransducers LDRs Vary resistance with illumination Ohmic As illumination increases, resistance decreases Advantages Disadvantages Simple, sensitive Very slow response Wide range time Can be used in voltage dividers
≡
Phototransistors Operate as transistors with base as light source
materials which can absorb large amounts of strain energy per unit volume before failing materials with little or no plastic region materials with a high value for Young’s Modulus *not needed* materials with a large plastic region how much stress a sample can be subjected to before failing flat points in an output signal caused by the input signal being out of range when the input voltage is greater than the linear region when the input voltage is less than the linear region the gain of an amplifier where the signal is not clipped the ‘DC blocking’ effect of a capacitor
one signal per wire skin effect thick fibres expensive affected by EM interference convenient to branch and join
or
Jargon
brittle
Equilibrium
Est
=
Remember that this energy is per unit volume
frequencies, limiting data transfer rates. This doesn’t
happen to optic fibres.
=
Area under
1
Low frequencies can travel along the entire wire, whereas high frequencies encounter more attenuation than low
σ∆ εσ ε ∆ σ σε ε ∴ Stress =
Young s Modulus = E =
2
Skin effect high frequencies can only travel along the skin. Therefore,
) and strain
Strain =
Parallel
1
Σ
thickness and therefore the same for every sample of a given material
Photodiodes Vary conductance (resistance) with illumination Non-ohmic Work in reverse bias Advantages Disadvantages Very fast Not sensitive response time
Glass fibre
1000+ signals per wire no skin effect thin fibres cheap not affected by EM interference inconvenient to branch and join
