definitions sheet (copy)

physical quantity

physical quantity

quantity that can be measured

has numerical value and unit

scalar

quantity with magnitude only

vector

quantity with magnitude and direction

distance

actual (curved) path travelled

displacement

straight-line distance between 2 points

speed

rate of change of distance

velocity

rate of change of displacement

instantaneous velocity

average velocity measured over an infinitesimally short time interval

instantaneous speed

speed at any given time

average speed

average of all instantaneous speeds

acceleration

rate of change of velocity

mass

the property of a body that resists change in motion

centre of mass

the point where an applied force does not cause any rotation

linear momentum

mass m multiplied by velocity v

newton’s 1st law

an object at rest will remain at rest or an object in motion will remain in motion provided no external force acts on the object

newton’s 2nd law

rate of change of momentum of a body is directly proportional to the external resultant force acting upon it and occurs in the direction of the force

f=ma

newton’s 3rd law

if body A exerts a force on body B, then body B exerts an equal but opposite force on body A

weight

gravitational force acting on the object

w = mg

centre of gravity

the point at which the whole weight of the body may be considered to act

viscous force/drag force

the frictional force exerted on a body when it moves through a fluid

principle conservation of momentum

the total momentum of a system remains constant provided no external forces act on the system (in a closed system)

OR

total momentum before collision is equal to total momentum after collision in any closed (isolated) system

elastic collision

if the total kinetic energy before collision is equal to the total kinetic energy after collision

inelastic collision

if the total kinetic energy before collision is NOT equal to the total kinetic energy after collision

moment of a force

the product of the force F and the perpendicular distance d from the pivot to the line of action of the force

m = F x perpendicular d

couple

two forces, equal in magnitude but opposite in direction whose lines of action do not coincide

torque of a couple

product of one of the forces and the perpendicular distance between the two forces

principle of moments

for a body to be in rotational equilibrium, the sum of clockwise moments must be equal to the sum of the anticlockwise moments about a pivot (point)

equilibrium of a body

resultant force is 0 in any direction and resultant moment or resultant torque is zero about any point

density ρ

mass over volume

pressure p

force acting per unit area

upthrust

difference in fluid pressure between the top and bottom surface of the object

archimedes’ principle

upthrust is equal to the weight of the fluid displaced when a body is wholly or partially immersed in a fluid

principle conservation of energy

energy can be converted from one form to another but cannot be destroyed

work done

the product of a force F and the distance s moved in the direction of the force

efficiency of a system

gives a measure of how much of the total energy may be considered useful and is not ‘lost’

power P

work done per unit time / rate of doing work

p = w/t

energy

the ability to do work

gravitational potential energy

energy possessed by a mass due to its position in a gravitational field

kinetic energy

energy stored to do work due to its motion

compressive forces

object squashed

tensile forces

object stretched

hooke’s law

states that provided the elastic limit is not exceeded, the extension e of a body is proportional to the applied force F

elastic limit

the point beyond which does not return to it original length when the force/load is removed

elastic constant/spring constant

force per unit extension

limit of proportionality

the point beyond where the extension is no longer proportional to the load even after more loads are added

stress

force F per unit area A

strain

extension e per unit length l

young modulus

ratio of stress to strain

E = Fl/Ae

elastic deformation

when the material returns to its original shape (length) once the applied force is removed

plastic deformation

when the material DOES NOT returns to its original shape (length) once the applied force is removed and is permanently deformed

strain energy

energy stored in a body due to change of shape

elastic energy

area under the graph

properties of a wave

refraction, diffraction, reflection, interference

ripple tank

an object used to study the basic properties of a wave

wavefront

an imaginary line that connects all points ona wave that are in the same phase

OR

a line that connects all crests of a wave

progressive waves

waves that transfer energy from one point of another without the transfer of matter

displacement (wave)

distance travelled in a specified direction from its rest position

amplitude

the maximum displacement of a wave

wavelength

shortest distance between points, which are vibrating in phase with each other

period T

time for a particle in the wave to complete one vibration, or one cycle

frequency f

he number of complete vibrations or cycles or waves per unit time of a point on the wave

speed v (wave)

is the speed with which the energy is transferred/speed of wavefront

phase (wave)

a term used to describe the relative positions of the crests or troughs of two different waves of the same frequency

in phase

when the crests and troughs of the two waves are aligned

antiphase

a measure of the fraction of a cycle or oscillation a particular point or wave is ahead or behind another point

phase difference

a measure of the fraction of a cycle or oscillation a particular point or wave is ahead or behind another point)

transverse waves

vibrations of the particles in the wave are at right angles to the direction in which energy of the wave is travelling

longitudinal waves

the direction of the vibrations of the particles in the wave is along the direction in which the energy of the wave is travelling

doppler effect

the frequency change due to the relative motion between a source of sound or light and an observer

em wave

interlocking electric and magnetic field oscillations at right angles to one another

polarised wave

a transverse wave in which vibrations occur in only one of the directions at right angles to the direction in which the wave energy is travelling

malus’s law

I=I⁰cos²θ

principle of superposition

when two or more waves meet at the same place at the same time, the resultant displacement is equal to the vector sum of the individual displacements of the waves at that point

stationary waves

waves that do not transfer energy along them

do not travel along the medium

standing waves

formation of stationary wave

an incident wave is reflected at a fixed end

a stationary wave is the result of interference between two (incident and reflected) waves of equal frequency and amplitude, travelling along the same line with the same speed but in opposite directions

nodes

points on the wave where amplitude is zero (particles do not oscillate)

antinodes

points on a wave where amplitude is maximum

diffraction

bending or spreading of waves into the geometrical shadow as it passes through an aperture or at an edge.

coherence

two waves having a constant phase relationship between them which originate from a single source

interference

sum/addition/combination of the displacements of coherent overlapping/meeting waves

When two or more coherent waves overlap, the resultant displacement is the vector sum of the individual displacements at that point, resulting in regions of maximum and minimum intensities.

formula for double slit interference

λ = ax/D

formula for multiple slit interference

dsinθ = nλ

electric current

rate of flow of charged particles

I = Q/t

electric charge

product of current and time during current flow

Q = It

area under I-t graph

coulomb

ampere second

quantization

discrete and equal amounts of charge.

formula for quantizised charge

Q = Ne

N = no of charged particles

e = elementary unit of charge

Ne = It

Q=It

Ne=It

potential difference

the energy W transferred (from electrical energy to other form of energy) per unit charge Q as it flows between two points in a circuit.

V = W/Q

volt

joule per coulomb

W = Pt

P = IV

resistance

ratio of pd across the conductor to the electric current I flowing in it

R = V/I

ohm

volt per unit ampere

resistivity

the resistance between opposite faces of a cube of the material, of unit length l and unit cross-sectional area A at a certain temperature.

R = pl/A

ohm’s law

states that the electric current I through a conductor is directly proportional to the potential difference V across it, provided its temperature remains constant.

electromotive force emf

is the energy W transferred (from other forms of energy to electrical energy) by a source in driving unit charge Q round a complete circuit.

internal resistance

resistance of the cell causing loss of voltage or energy loss in cell

E = terminal p. d.+, lost volts′

E = VR + Vr

E = IR + Ir

E = I(R+r)

If the external resistance R increases, the current I decreases and the terminal p.d. V increases as the ‘lost volt’ due to internal resistance r decreases.

If the external resistance R decreases, the current I increases and the terminal p.d. V decreases as the ‘lost volt’ due to internal resistance r increases.

-

Effect of internal resistance on the output power

A battery delivers maximum power to a circuit when the load resistance of the circuit is equal to the internal resistance of the battery.

efficiency of a circuit

IV/IE