# 36166687 vce physics unit 3 exam 1 cheat sheet final copy

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MOTION NEWTONS LAWS (TAKEN FROM CENTRE OF MASS) 1.

2.

3.

Inertia An object at rest will remain at rest An object in motion will remain in uniform motion Unless acted upon by a net unbalanced force F = ma Acceleration is directly proportional (and in line with) the net force acting on an object Acceleration is indirectly proportional to mass When object A exerts a force on object B, object B exerts an equal and opposite force on object A

Vertical Circular Motion Object mass m, tension in string, T: mv 2 Highest: T + mg = r mv 2 Lowest: T mg = r

E k1 + U g1 = E k2 + U g2

Gravitational Potential Energy @ the Earths surface: Ug = mgh

GENERAL EQUATIONS Power: P = IV V2 P= R P = I 2 R V = IR E = VIt = Pt Q = It

increases with increasing forward current.

POWER

Ug = mgh

PROJECTILE MOTION

Ug is given by the area under a force- distance, or field-distance graph Spring Energy

Ptotal = P = P1 + P2 + P3 + ... Ptotal = VABI Ptotal = VAB2 R total

Projectile M otion

Hookes Law: when an object interacts with a Hookean spring, kinetic energy is changed to elastic potential energy and vice versa. Total energy remains constant. F = kx E k1 + U e1 = E k2 + U e2

Ptotal = I 2 Rtotal

Modulation: Changing the intensity of the carrier light wave to replicate the amplitude variation of the signal wave Allows signals that are more robust and able to travel longer distances. Demodulation: Separation of a signal wave from the carrier wave.

RESISTANCE

CURRENT

The ability of a conductor to resist the flow of electric current. Ohms Law Ohms law states that for ohmic conductors, the resistance stays constant, when voltage and current vary. V V = IR , R = I Resistance in Parallel 1 1 1 1 = + + + ... or RP R1 R2 R3RP = 1 1 1 1 + + + ... R1 R2 R3

NET FORCE

Calculated from addition of vectors: 1. 1D: Addition of magnitude 2. 2D: Vectors head-to-tail or resolution into two perpendicular components

UNIFORM CIRCULAR MOTION

2D motion under a constant force (gravity, or weight) Horizontal component of velocity vector remains constant Vertical component of velocity vector is affected by gravity, constant acceleration of g downwards. For horizontal component: a = 0 , v = u = Vcos , s = ut V = speed at angle to horiz. For vertical component: Use rules for rectilinear motion:

Ue = 1 kx 2 2 Area under force-extension graph is change in elastic potential energy U e = 1 k(x 2 ) 2 1 k(x1) 2 2 2

POTENTIAL DIFFERENCE/VOLTAGE The change in electrical potential energy between two points. Voltage Dividers

STRUCTURES AND MATERIALS

k=

YA l

v = u + at1 2

s = (u + v) General Diagrams

s = ut + 1 at 2 2 s = vt at

1 2 , v = or v = 2rf T T Velocity is tangential to the motion path Magnitude of acceleration: 2 2 a = v or a = 4 r or a = 4 2 rf 2 r T2 Centripetal acceleration: Acceleration is always toward the centre of the circle Velocity and acceleration are NOT constant (always changing) Velocity is perpendicular to acceleration Net Force MUST be toward the centre of the circle (centripetal force) to sustain circular motion f =

1 2

2

u = Vsin , a = g

v 2 = u 2 + 2as

MOMENTUM & ENERGY Impulse Impulse = change in momentum: I = p , Ft = mv mu Conservation of momentum: Total momentum before = total momentum after m1u1 + m 2 u2 = m1v1 + m 2v 2 When one object gains momentum, the other loses momentum by the same amount. (The total remains constant) p2 = p1 , I2 = I1

Elastic collision Elastic collision: Total kinetic energy before and after collision is equal. (Energy is conserved) During collision some kinetic energy is converted to elastic potential energy, and then back again Inelastic collision: Energy after collision is less than energy before. (Energy is lost) During collision, some kinetic energy is converted to heat and sound. Gravitational fields Universal gravitational field: GM g = 2 r Gravitational force between and two objects: GM1M 2 F= r2 Satellite Motion: a = g

Voltage Dividers

V RP = AB I

Resistance in Series RS = R1 + R2 + R3 + ... V RS = AB I Non-ohmic conductors Diodes: Device used to control current and voltage Conducts when forward biased Current drops to virtually 0 in reverse-bias Thermistors: Resistance varies with temperature Transducers: Change other forms of energy (heat, light, etc.) into electricity and vice versa. Photonic Transducers: Change light into electricity and vice versa. Light Dependant Resistors (LDRs): Resistance changes with the intensity of light it is exposed to Photodiodes: Conductivity changes with illuminating light intensity when in reverse-bias (photoconductive mode) As light intensity increases, current (photocurrent) increases. Forward biased mode is called photovoltaic mode. Light Emitting Diodes (LEDs): Emits light when forward biased. Light intensity

A series connection of two or more resistors forms a voltage divider. The supply voltage V1 R = 1 V2 R2 Vout = Rout Vin R1 + R23

General Diagrams

FORCES Tension and Compression When a When a structure/material is pulled at both ends/stretched, it is under tension. When a structure/material is pushed at both ends/squashed, it is under compression. Compression and tension forces are taken overall, i.e.: a material of non-uniform cross-sectional area experiences uniform compression and tension. Compression and tension can coexist in a structure. Shear Where two opposing parallel forces in the same plane are applied to opposite sides of a structure/material, or, when two opposing rotational forces in the same plane are applied to a structure/material, it is experiencing a shear force.

Banked Track 3 forces: 1. Normal force 2. Weight force 3. Friction force Fcent = Fnet = N + W mv 2 Fcent = = mg tan r v2 = = g tan r Resolve Normal and Friction forces into vertical and horizontal components Sum of vertical components = 0 Sum of horizontal components = ma Maximum speed: when friction reaches maximum Design speed: when friction = 0,

ELECTRONICS

v 2 GM 4 2 r GM = 2 or = 2 r r T2 r 3 r GM v 2 r = GM or 2 = T 4 2

Voltage Amplification Voltage gain: Vout gain = Vin i.e.: gain is gradient of voltage in-out graph. Voltage Negative value for Amplification inverting, positive for in-out graph non-inverting. If input signal exceeds maximum, clipping occurs. 2 1 -3 -2 -1 0 1 2 -1 -2 -3

3

2.5

0

2.5

5

7.5

10

12.5

15

Work Work is done by one system on another system during which the former exerts a force on the latter. (energy transfer) Change in Kinetic Energy Results from work done by net force on an object. Fs = 1 mv 2 1 mu 2 2 2 When an object moves in a gravitational field kinetic energy changes to gravitational energy, and vice versa. Total energy remains constant

-2.5

Clipping

PHOTONICS Frequency Modulation carrier w ave

EFFECTS OF FORCES/ENERGY Stress, Strain and Youngs Modulus Stress is experienced by any material subjected to a force. Because stress is inversely proportional to cross-sectional area, thinner materials experience more stress (and more likely to fail) F = A 1 , F A

output w ave

v = gr tan , where is the banking

angle

General Diagrams

signal w ave

Signal M odulation

Strain is the relative (fractional/percentage) change in length of a material under stress. l = l Youngs Modulus is unique to the material. It is the linear relationship between stress and strain in a material. It is a measure of stiffness of a material In diagrams, A is stiffer than B It is given by the gradient of a stress-strain graph. Y = Elasticity An elastic material has the same stress strain graph (Y value) when stress is applied or removed When stress is removed, the material returns to its original shape. This is elastic behaviour The elastic region of the stress-strain graph is linear, and is followed by the plastic region. When the elastic limit is reached, however, the material begins to exhibit plastic behaviour, and is permanently deformed (plastic deformation) If stress is applied beyond the elastic limit, the material will eventually reach its breaking point, where it will fail (break) Strength The maximum stress (compressive or tensile) a material can withstand before failing is its compressive/tensile strength Strain energy is the amount of potential energy stored in material under stress. It is given by the area under the force- extension graph. Also given by multiplying the area under the stress- strain graph by the volume of the material E (J) = Vol (m3 ) A -

compression and stronger under tension) rods or mesh during pouring. This concrete is called reinforced concrete Pre-stressed concrete is where (texturedfor grip) steel rods are under tension while the concrete is poured around them. When the concrete is set, the rods are released the concrete is under compression (it strongest state) and the steel is under tension (its strongest state) The same outcome is achieved in post-stressed concrete where smooth steel rods are inse