# Physics AQA unit 2

Covering topics:

• P21: Motion
• P22: Speeding up and slowing down
• P23: Work, energy and momentum
• P24:Static electricity
• P25:Current electricity
• P26: Mains electricity
• p27: Nuclear physics
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• Created by: J
• Created on: 23-04-11 15:47

## Motion: distance time graphs

MOTION

Distance time graphs

Y axis= distance (M) x axis= time (S) , slope represents speed, steeper slope means greater speed.

To calculate speed, calculate gradient of line= change in y/change in x

Horizontal line= stationary body

Rapidly increasing= constant high speed

speed(m/s)= distance (m)/Time (s)

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## Motion: velocity time graph

MOTION

Velocity time graph

y axis= velocity, x axis= time, shows accelration, calculationg gradient shows acceleration, calculating area under line shows distance travelled

horizontal line= constant speed

positive line= constant acceleration

negative line= constant decceleration

accelearation (m/s2) =change in velocity (m)/ time taken for change (s)

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## speeding up and slowing down

SPEEDING UP AND SLOWING DOWN

When objects interact they always exert equal and opposite forces (Newtons law), the unit of force is a newton

Resultant force= the single force that would have the same effect on the object as all the orginal forces acting together

Resulatant force(N)= mass (kg)/ acceleration(m/s2)

Bigger resultant force= greater acceleration

At rest, with resultant force 0 the object stays at rest

A moving object with resultant force 0 the velocity stays the same

A moving object resultant force above 0 affecting the same direction accelerates

moving objecresultant force above 0 affecting the opposite direction decelerates

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## speeding up and slowing down

SPEEDING UP AND SLOWING DOWN

Thinking distance= distance travelled by vechile in time taken for driver to react

Breaking distance= distance the vechile travels under braking force

stopping distance = thinking distance+ braking distance

Falling objects

Weight= force of gravity on object

weight (N)= mass (kg) x acceleration due to gravity (m/s2)

Terminal velocity= when an object falls through a fluid air resisitance is created, the faster the object falls the more friction is exerted, the faster the object falls the more friction is created so the forces become equal and it tavels at a constant velocity.

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## Work, energy and momentum

WORK, ENERGY AND MOMENTUM

Work done= energy transferred, when work id one against friction mostly heat (thermal) energy is produced

Work done (j) =force (N) x diatance moved (m)

Kinetic energy, depends on mass and speed

Kinetic energy=1/2 massx speed 2

All moving objects have momentum,

momentum (kgm/s) = mass (kg)  x velocity (m/s)

Momentum is conserved when objects interact as long as no external forces act on them. Momentum has a size and a direction.

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## Work, energy and momentum

WORK, ENERGY AND MOMENTUM

Collisions and explosions

In an explosion objects move apart with equal and opposite momentum, one positive, one negative. Therefore total momentum=0.

In a collision the objects may move together or apart. In a collision the momentum of an object often becomes 0 , if impact is short, the forces are large as impact increases, forces become less.

Changes in momentum

force (N) = change in momentum (kgm/s)/ time taken (s)

Car design- crumple zone-increases impact time

Air bag- changes moentum slowly, so force is less

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## Static electricity

STATIC ELECTRICITY

Electrical charges

like charges repeal

opposites attract

loss of electrons gives positive charge and gain of electrons gives negative charge

bigger the distance the weaker the force

current- rate of flow of charge

metals good conductors as have free electrons however insulators- electrons held in atoms. conductor only charges if away from ground otherwise discharges to the ground.Bigger charge on isolated object- higher potential differne therefore may spark across gap between object and earth conductor.

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## Static electricity: Electrostatic precipitators di 1. Smoke particles pick up a negative charge.
2. Smoke particles are attracted to the collecting plates.
3. Collecting plates are knocked to remove the smoke particles.
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## Current electricity: circuit symbols 9 of 22

## Static electricity:photocopier diagram 10 of 22

## current electricity: potential difference graphs

CURRENT ELECTRICITY A current- potential difference graph for a filament lamp, as current increases, resistance increases reversing potential difference makes no differnence

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## current electricity: potential difference graphs A curent potentail differnece graph for a diode, as current moves in one direction only, reverse direection the diode has a very high resistance to current 0.

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## current electricity: resistance current through a resistor at constant temperature is directly proportional to the potetnial difference across the resistor. Resistnace (ohms)= potential differnce (v)

Current(A)

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## current electricity: Series circuit and parallel c

Series circuit

current= Potential differnce

Total resitance

• current is same in each component
• potential differneces add to give total potential differnce
• resistnaces add to give total resistance

Parallel circuit

• Potentail differnece is same across each component
• total current is sum of cureents through each component
• bigger resistance of component, the smaller the current is.
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## Mains electricity

MAINS ELCETRICITY

Alternating current (a.c.)repeatedly reverses its direction, its mains elexctricity. Which alternates between positive and negative potentila with resopect to neutral wire. Between +325 and -325 so 230 volts direct potentail differnece

England mains =230v and 50Hertz

Direct current (d.c.) current passes round circuit in one direction

It can be dangerous so dont use overlong/frayed cables, use near extreme heat or water,overload with adaptor, plugs,extensions etc.

Metal cased appliances need to be earthed, but plastic dont as "double insulated" and connected to supply with two-core cablle containing live and neutral wire.

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## Mains electricity: plugs Wiring a plug, Outer cover made of plastic- good inulator, pins out of brass good conductor, wont oxidize or rust. NO bare wires should show, cable grip should fasten over cable, correct wires to correct terminals

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## Mains electricity: fuses and circuit breakers

Fuses- contain thin wires, which heats and melts and cuts current of, if it becomes to big. Used in appliances with metal cases, if fault develops large current flows to earth and melts to prevent electric shock.

Circuit breaker: an electromagnetic switch that opens ie. trips and cuts the currnet if to much passes through ( can be used instead of fuse)

an electrical  device transforms electrical energy to other forms and transfers energy form one place to another.

Power(W) =energy transformed(j)

time (s)

its more usual to measure current through a device and potentail difffernec across it you can also use current and p.d to calculate power.

Power(W)- current (A) x potential differnece (V)

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## Mains electricity: electrical energy and charge

An electric current is the rate of charge

When charge flows through a resistor, electrical energy is transformed into heat energy.

energy transformed (j) =potential differnece (v) x charge (c)

(charge is measured in coulombs)

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## Nuclear physics

Nuclear reactions

alpha decay = nucleus loses 2 protons and 2 neutrons, and ammits 2 protons and 2 neutons

Beta decay=  a neutron in the nucleus cahnges into a proton, and an electron is craeted in the nucleus and instantly emitted.

Atomic number= number of protons

Mass number= number of protons and neutrons

Background radiation: is present all the time, it comes from rocks, cosmic rays, nucler power stations etc.

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## Nuclear physics: Discovery of the nucleus

Discovery of the nucleus

Plum pudding theory- spheres of positive cahrge with electrons stuck in

Rutherford, Geiger and Marsden devised a particle scattering experiment where they fired particles at thin gold leaf

Most alpha particles went straight thtough foil, meaning most of atom is emopty spcae, some were deflected therough small angels, therefore nucleus haa positive ccharge. a few rebound meaning nucleus has large mass and big + charge

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## Nuclear physic: Nuclear fission

NUCLEAR FISSION

Occurs when a neutron collides with and splits a uranium 235 nucleus or sa plutonium 239 nucleus

A chain reaction occurs when neutrons from the fission go on to caus efurther fision

NUCLEAR FUSION.

Nuclear fusion is the joining of 2 nuclei to form a single, larger nucleus.

Energy is released

It has to be heated to very high temperatures, to overcome repulsion and fuse, it has t be contained by a magnetic field.

e.g. natural occurence = sun

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## Key

/= divided by

m/s2= squared

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These notes are really good for revision although there are a lot of spelling mistakes which sometimes made it difficult to understand! still rate it 5 though

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It is very helpful, although there are a lot of spelling errors which did confuse me, but still very helpful!

Thank You

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Thanks really helped with my physic exam x

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