Physics NEED TO KNOW

Explain the variations in intensity (sound/light)

«incidentand reflected»waves superpose/interfere/combine ✓

«that leads to»standing waves formed OR nodes and antinodes present✓

at antinodes / maxima there is maximum intensity / constructive interference / «displacement»addition / louder sound ✓

at nodes / minima there is minimum intensity / destructive interference / «displacement» cancellation / quieter sound ✓

Wavelength given distance between 2 adj. min/max

MULTIPLY BY 2!

why is it a weak interaction?

strangeness is not conserved and this is possible only in weak interactions

the weak interaction allows change of quark flavour

only the weak interaction has a boson / an exchange particle / a W+ to conserve the charge

neutrinos are only produced via the weak interaction ✓

binary star system

two stars orbiting around a common centre of mass/gravity

why are cephids called standard candles and used as those

cephids have a known average luminosity

which is determined from the measurement of a period

\---

determined from period-luminosity graphs

can be used to estimate the distance of galaxies

What are the S.I. fundamental units?

kilogram, metre, second, ampere, mole, Kelvin

PRECISION

the closeness of all the results agreeing with one another

ACCURACY

how close the results appear to be to the true or accepted value

PROPORTIONAL

When two quantities plotted on a graph produce a straight line that passes through the ORIGIN (0,0)

VECTOR

A quantity that has both magnitude and direction

SCALAR

A quantity that possesses only magnitude.

What are Vector Quantities?

displacement, velocity, acceleration, momentum, impulse, ALL FORCES, ALL FIELDS.

What is the horizontal component to a Vector R?

R cos θ

What is the vertical component to a Vector R?

R sin θ

DISPLACEMENT, 's'

distance moved in a particular direction or shortest distance between 2 points.

VELOCITY, 'u' or 'v'

rate of change of displacement (VECTOR)

SPEED,

rate of change of distance (SCALAR)

ACCELERATION, 'a'

rate of change of velocity (VECTOR)

INSTANTANEOUS

the measured quantity at that moment in time

AVERAGE

the total measured quantity with respect to the total time taken to measure that quantity

When can the equations of motion be used?

only if the acceleration is constant.

FREE-FALL

Ignoring air resistance, the vertical motion of an object that undergoes uniform acceleration in a uniform gravitational field

TERMINAL SPEED or VELOCITY

The maximum speed reached by a free-falling object in a uniform gravitational field, when air resistance is acting.

FORCES

Pushing and pulling effects - that cause a CHANGE in the velocity of an object.

BALANCED FORCES

When no linear resultant force is acting, an object moves at constant velocity. (No acceleration)

RESULTANT or NET FORCE

When an acceleration occurs on an object. (Velocity is changing). The overall force acting.

WEIGHT, 'W'

The name given to the force of gravity that acts on matter (mass) that pulls it vertically down. W \= m g

FRICTION

The force that acts between the contact of surfaces and opposes motion. (always acts in opposite direction to the motion of the object)

NORMAL REACTION

The perpendicular force that acts in the opposite direction to a point of contact.

TENSION

The force that acts when the object undergoes a pulling force. Tension acts towards the points of connection.

COMPRESSION

The force that acts when the object undergoes a pushing force. Compression acts away from the points of connection.

UPTHRUST

The force exerted by the Pressure of a fluid over an area of the object.

LIFT

The force caused on a object due to a pressure difference, causing the object to vertically rise.

What is Newton's First Law of Motion?

Every object continues in its state of rest or uniform motion in a straight line, unless an external force acts on it.

(The Inertial Law)

What is Translational Equilibrium?

The resultant forces acting in ANY (linear) DIRECTION on the object is zero.

What is Newton's Second Law of Motion?

The resultant force on an object is proportional to the rate of change of momentum.

If the amount of mass stays constant, then 'the resultant force is proportional to the acceleration' F \= m a

(The resultant force law)

What is Newton's Third Law of Motion?

When two bodies A and B interact, the force that A exerts on B is equal and opposite to the force that B exerts on A.

(The Pair force law)

LINEAR MOMENTUM, 'p'

The product of the mass and velocity of an object

IMPULSE

The change of momentum, or, the product of the Force acting on an object and the time it acts on the object

What is the Law of Conservation of Linear Momentum?

The total linear momentum of a system of interacting particles remains constant provided there is no resultant external force acting

WORK DONE

Work is done if a force and the displacement are in the same direction (SCALAR) W.d. \= F s cos θ

(When energy is transferred, Work is done!)

KINETIC ENERGY

Any object that is in motion posesses Kinetic Energy

(SCALAR) K.E. \= 1/2 m v^2

\[moving energy]

POTENTIAL ENERGY

The energy stored in an object to have the ability to perform Work, due to its position of state. (SCALAR)

In a gravitational field, its position due to change in height.

G.P.E. \= m g ∆h

In a Spring, due to compression or tension.

Elastic P.E. \= 1/2 k x^2

\[stored energy]

ELASTIC COLLISIONS / EXPLOSIONS

When the linear momentum of interacting bodies in a system and their Kinetic Energies are both conserved.

INELASTIC COLLISIONS / EXPLOSIONS

When only the linear momentum of interacting bodies in a system is conserved, but the Kinetic Energies undergo a change. Some of which is degraded as thermal energy.

POWER

The rate at which energy is transferred or the Work is done

EFFICIENCY

The ratio of the useful output quantity with respect to the total input quantity

CENTRIPETAL ACCELERATION

A particle or body that undergoes uniform circular motion, due to constantly changing direction.

Acceleration occurs even if the object moving in the circle is at constant speed.

CENTRIPETAL FORCE

The resultant Force needed to cause the centripetal acceleration, and always acts towards the centre of circular motion.

THERMAL EQUILIBRIUM

When two objects, in contact, at different temperatures, transfer thermal energy from the higher temperature object to cooler temperature object, until the temperatures of both objects are identical then no more thermal energy is transferred between them.

INTERNAL ENERGY (microscopic)

The total potential energy and random kinetic energy of the molecules of the substance

TEMPERATURE (macroscopic)

The measure of an object's 'hotness', by using a measuring device - thermometer.

THERMAL ENERGY

The energy that is transferred through the processes of Conduction, Convection and Radiation of objects.

MOLE

Is the amount of substance that contains the same number of atoms as 0.012 kg of carbon-12

MOLAR MASS

The mass of one mole of the substance weighed out in grams

AVOGADRO CONSTANT

The number of atoms in 0.012 kg of carbon-12. It is 6.02 x 10^23

SPECIFIC HEAT CAPACITY

The energy required to raise the temperature of a unit mass of a subtance by 1K.

THERMAL (HEAT) CAPACITY

The energy required to raise the the temperature of a substance by 1K.

EVAPORATION

Occurs at the Liquid surface, where a liquid changes its state to a gas, that has not reached the boiling point of the liquid. (It causes cooling)

BOILING

Occurs when the vapour pressure of the liquid equals the atmospheric pressure, and the liquid changes state to a gas, without a temperature change. It occurs through the liquid.

SPECIFIC LATENT HEAT

The amount of energy per unit mass absorbed or released during a change of phase

PRESSURE

The force that acts per unit area on a surface

TEMPERATURE

Is a measure of the average random kinetic energy of the molecules in a substance

DISPLACEMENT in waves

The instantaneous distance of the moving object from its mean (equilibrium) position (in a specified direction)

AMPLITUDE

The maximum displacement from the mean (equilibrium) position

FREQUENCY, 'f'

The number of oscillations completed per unit time.

f \= 1/T

PERIOD, 'T'

The time taken for one complete oscillation or cycle.

T \= 1/f

PHASE DIFFERENCE

The measure of how 'in step' different particles are in a wave cycle.

SIMPLE HARMONIC MOTION - S.H.M.

The motion that takes place when the acceleration of an object is always directed towards its mean (equilibrium) position and is proportional to its displacement from the mean (equilibrium) position.

a \= - ω^2 x

WAVE PULSE

One oscillation that occurs in the system

CONTINUOUS PROGRESSIVE (TRAVELLING) WAVE

Involves a succession of continuing individual oscillations

TRANSVERSE WAVES

When the oscillation direction of the particles is perpendicular (right angles) to the wave energy transfer or propagation

LONGITUDINAL WAVES

When the oscillation direction of the particles is parallel to the wave energy transfer or propagation

WAVEFRONT

The imaginary line that signifies the part on the wave that are moving together, e.g. a crest of wave or a trough of the wave. It is perpendicular to the ray.