Unit 1 AS Physics WJEC

what are the 7 base units

kg m s a kelvin/celsius mole candela

velocity =

displacement / time

vector quantities

displacement velocity acceleration force momentum gravity

define centre of gravity

the point where all the weight of an object appears to act

principle of moments

in order for an object to remain balanced, the total clockwise moment must equal the total anticlockwise moment

moment =

force x perpendicular distance between line of action of the force and the pivot

stability definition

line of action of weight must fall within base

newton’s first law

an object’s velocity will remain constant providing there is no resultant external force

newton’s second law

f = ma

newton’s third law

if object a exerts a force on object b then object b will exert and equal and opposite force on object a

moments are measured in

newton metres

conditions needed for an object to stay in equilibrium

resultant force is zero, resultant moment is zero

percentage uncertainty =

absolute / measured value x 100

when multiplying / dividing uncertainty

add percentage uncertainty

when adding or subtracting uncertainty

add absolute uncertainty

what happens to uncertainty when x is squared

x 2

displacement time graphs gradient =

velocity

velocity time graphs gradient =

acceleration

velocity time graphs displacement =

area

xuvat is used for

uniform acceleration

define force xuvat

rate of transfer of momentum

acceleration definition

rate of change of velocity

for xuvat dont forget

decide which direction is positive

what is instantaneous speed

rate of change of distance

a projectile is

something initially propelled by an external force and moves freely under the influence of gravity

kinematics practical plots what

height against time squared

how to find g for kinematics practical

2 x gradient

rules for newton’s third law pairs

act on separate bodies, same force, equal in size, opposite in direction, act along a straight line

momentum =

mass x velocity

force =

change in momentum / time

momentum time graph gradient =

force

conservation of momentum

the vector sum of momentum in a system remains constant provided no external resultant force acts

elastic collision =

no change in kinetic energy

inelastic collision =

kinetic energy lost

what does normal mean

90 degrees

weight =

mg

newton’s second law practical with a constant mass, what is the equation?

a is prop to f, gradient = 1/m

newton’s second law practical with constant mass

measure time, find velocity then acceleration, then plot acceleration against force

newton’s second law practical but mass on rider changes, what is the equation?

a is prop to 1/m, gradient = force

newton’s second law practical what do you plot when mass changes

acceleration against 1/m

work done =

force x distance moved in the direction of the force

if work done is in a different direction to displacement =

f X cos theta

if theta is 90 degrees, what is work done

0

if theta is greater than 90 degrees, what is work done

negative

what is the law of conservation of energy

energy cannot be created or destroyed, only transferred between stores

power =

force x velocity

efficiency definition

proportion of useful energy transferred from the total energy available

power (normal equation)

work done / time

kinetic energy =

½ m v squared

gpe =

mgh

change in kinetic energy =

½ mv squared - ½ mu squared

change in kinetic energy if work done is ON object

final - initial

change in kinetic energy if work done is BY object

initial - final

elastic energy =

½ k X squared

spring constant equation

f = kx

work done for stretching a spring =

½ f X

typical dynamics question equation

gpe = work done against resistive forces + ke

what is the spring constant

force per unit extension

what does the gradient of parallel springs look like

steeper

what does the gradient of series springs look like

shallower

how to find work done in hookes law

area under graph

symbol for stress

sigma

symbol for strain

epsilon

stress =

force / area

strain =

change in length / original length

unit of stress

newtons per square metre

young modulus

stress / strain

what is the range of young modulus values

100GPa

work done in hooke’s law equation

1/2kx squared

work done equation for area of graph

½ f x

phenomenon of loading and unloading a rubber band name

hysteresis

area under loading curve =

work done on rubber in extension

area under unloading curve =

work done by rubber during constriction

what is it called when a material narrows when its stretched

necking

what is the point on a stress strain graph called after the limit of proportionality

yield strength or yield stress

what are the properties of radio waves

low energy, long wavelength, low frequency

what are the properties of gamma rays

high energy, short wavelength, high frequency

define EM spectrum

the name of the range of energies of radiation which can be given off by charged particles

a star spectrum consists of

a continuous spectrum at the surface of the star, and specific absorption lines due to the passage of radiation through gases in the stars atmosphere

emission spectrum looks like

black with colourful lines

absorption spectrum looks like

colourful with black lines

what is a perfect black body

perfectly absorbs all electromagnetic radiation

hotter star has what graph

taller peak

what colours are hot stars, medium stars and cold stars

blue white red

what graph has the peak (stars)

intensity wavelength

wien’s law

highest wavelength = constant / temp

stefan boltzmann law

power or luminosity = constant x area x temp 4

inverse square law equation for stars

intensity = power or luminosity / 4 x pi x distance to object (R) squared

what things are observed with radio waves

galaxies and their magnetic fields and jets

what things are observed with infrared

exoplanets and their formation

what things are observed with visible light

galaxies and their structure

what things are observed with UV

young stars and star formation

what things are observed with x rays

black holes and matter falling into them

what things are observed with gamma rays

gamma ray bursts and quasars, explosions powered by supermassive black holes

what is a quasar

bright galactic core with sm blackhole

what is a pulsar

neutron star which spins and emits radiowaves

what is a nebula

cloud of gas and dust

what is an accretion disk

forms around massive objects

what are the four fundamental forces of nature

weak forces, strong forces, gravity, electromagnetism

charge of up quark

plus two thirds