physics

weight

force a body exerts due to the pull of gravity

mass

the measure of the amount of material in a body

weight=

mass x velocity

objects are stable if

lower com

large surface area

objects will topple if

vertical line through the com falls outside the base

a moment is produced which causes the object to rotate

com is

the point where all the mass of that object may be considered to be

balance at com because

the moments on each side are equal

density is

mass per unit volume

density=

mass/volume

density tells us

how closely the particles are packed

friction is

a force that opposes motion

air resistance or drag

occurs when the object moves through air or fluid

reduce friction by

lubrication

changing the material or fluid

rollers

streamlining

friction acts in the

opposite direction of the object

friction exists

when two surfaces move over each other

a force can

change the direction of motion

change the shape of things

start objects moving and slowing down

2 main groups

contact and distant

contact

forces touch the object and produce a change of shape or state of motion

distant

forces act at a distance

1st law

a body will remain at rest or move at a constant velocity if the resultant force acting on the body is zero

balanced forces exist when

two forces act in opposite directions but are the same size

2nd law

if a resultant force acts on a body the body will not remain at rest or move at constant velocity, it will accelerate

resultant force=

mass x acceleration

principal of moments

when a object is balanced, the total sum of the clockwise moments is equal to the sum of the anticlockwise moments, about the pivot

distance is

ground covered

displacement is

shortest distance from start to finish in a certain direction

speed is

rate of change of distance

velocity is

rate of change in displacement

acceleration is

rate of change in velocity

scalar

magnitude

vector

magnitude and direction

acceleration=

velocity/time

unit of acceleration

m/s²

moment=

force x distance

unit of moments

newton metre

unit of density

kg/m³

size of moment depends on

size of force

distance of force from pivot

centrepedal force depends on

mass of object

speed of object

radius of orbit

momentum

amount of movement in a body

unit of momentum

kgm/s²

change in momentum=

force x distance

momentum depends on

mass

velocity

momentum=

mass x velocity

principle of momentum

when two bodies collide, the total momentum remains constant, providing that there are no external forces acting

energy types

kinetic

light

sound

EPE

GPE

chemical

electrical

nuclear

magnetic

heat

kinetic

movement in sport

light

bulb

heat

radiator

sound

radio

chemical

battery

magnetic

magnet

EPE

rubber band

GPE

anything above the ground

electrical

pylon

nuclear

inside nucleus

unit of energy

joules

efficiency=

useful out/total in

word down=

force x distance moved

kinetic energy=

½mv²

principle of energy

energy cannot be created or destroyed, only changed into different forms

power

rate at which work is done or energy is transferred

power=

work done/time

a fossil fuels

transporting oil and gas to power stations

d fossil fuels

strip mining destroys large areas of landscape

a nuclear

produces small amount of waste

d nuclear

waste produced is very, very dangerous

a geothermal

no fuel is needed

d geothermal

hazardous gases and minerals may come up from underground

a wind

free and wind farms need no fuel

d wind

wind is not always predictable

a hydro-electricity

no waste or pollution is produced

d hydro-electricity

water quality and quantity can be effected downstream which may have an impact on plant life

a tidal

tides are totally predictable

d tidal

few suitable sites for tidal barrages

a solar

produces no waste or pollution

d solar

doesn't work at night

a wave

can produce a great deal of energy

d wave

need a suitable site where waves are consistently strong

a biomass

less demand on fossil fuels

d biomass

makes green house gases

thermionic emission

current goes through a metal wire and gets so hot that it emits particles

Democritus

introduced the idea of building blocks

Dalton

introduced the idea of atoms

JJ Thompson

plum pudding model

a sphere of positive charge with tiny negative electrons stuck in it

Rutherford

fired positively charged alpha particles at a thin gold foil

most alpha particles went straight through with no or little deflection

some were deflected through very large angles and a few came straight back

introduced nucleus

Chadwick

discovered the neutron

Bohr

introduced the idea of electrons orbiting a nucleus un discrete energy levels, by studying the emission spectra of gases

an unstable atoms has

more neutrons

alpha α

⁴

He

₂

helium nucleus

big heavy slow

positively charged

poor penetration-stopped by paper

strong ionisation

deflected by magnetic field

beta β

⁰

e

-₁

fast moving electrons

negatively charged

greater penetration-stopped by al

moderate ionisation

deflected by magnetic field

gamma Ɣ

high frequency electromagnetic transverse waves

great penetration-stopped by thick lead or concrete

weakly ionising

no mass

magnetic field has no effect

half life

time taken for half the radioactive nuclei to decay

eg radiation

radon and thoron

cosmic rays

the body

nuclear fission

This is when heavy nuclei can be forced to split into two lighter nuclei

nuclear fission 2

Uranium-235 can be split into two lighter nuclei when it is struck by a slow neutron. The products produced move apart at very high speed, carrying with them a vast amount of energy.

At the same time 2 or 3 fast neutrons are also produced.

control rods

absorb neutrons

moderator

slow neutrons down

a nuclear fission

heat energy produced is used to produce electricity

d nuclear fission

fission fragments are radioactive. this radioactive waste must be extracted and disposed of. this is difficult and expensive.

nuclear fussion

this is when two lighter nuclei combine to form a single heavier nucleus