AQA P2 Physics Booster 2012 Specification E Ralls.

AQA P2 Physics Booster

2012 Specification

E Ralls

Remember your

units:

Weight = newtons (N)

Acceleration = m/s2

Work done = joules (J)

P2.1: Motion

Speed = Distance ÷ TimeThis will not be on your data sheet

Distance – time graphs

Speed vs. Velocity

Speed is simply how fast you are travelling…

Velocity is “speed in a given direction”…

This car is travelling at a speed of 20m/s

This car is travelling at a velocity of 20m/s east

Velocity-time graphs

80

60

40

20

0

10 20 30 40 50

Velocity

m/s

Time (s)

accelerating

constant speed/velocity

accelerating

decelerating

Acceleration vs. Deceleration

Remember, if you are asked to work out the deceleration of an object, you use the same equation as you would to work out acceleration.

P2.2: Forces

Newton said:

Objects continue to move in a state of constant velocity unless acted upon by an external net force.

1ST LAW.

Newton

Astronauts need to beware!

Newton

Newton also said:“Every action has an equaland opposite reaction.” - His 3rd law.

Which explains why guns recoil and how rocket engines work.

Another example of the third law; this time to stop the astronaut moving.

Resultant Force

When the resultant force on an object is not zero, movement depends on the size and direction of the resultant force.

Resultant Force

60N

20N

40N

AccelerationThe acceleration of an object depends on the size of the resultant force.

If the resultant force is zero the object will remain motionless or continue at a constant speed.

Wind 2N

Engine 4N

Air resistance 3N

Resultant Force 3N

Braking ForceThe braking force needed to stop a vehicle is dependant on:

• The velocity of the vehicle when the brakes are first applied.

• The mass of the vehicle.

Stopping Distance

Stopping distance

Thinking distance

Braking distance

Stopping Distance

Factors Affecting Stopping Distance

Tiredness, alcohol and drugs

The speed that the vehicle is travelling

Adverse road conditions

Poorly maintained vehicle

Weight and MassMass = the quantity of matter in an objectWeight = the force of gravity on an object

The gravitational field strength of Earth is about

10N/kg

Weight and Mass

Air Resistance

Elastic Potential EnergyAn elastic object such as a spring stores elastic potential energy when stretched or squashed.

Work is done on an elastic object when its shape changes and it stores elastic potential energy.

Energy transferred by a force

Hooke’s Law“The extension of an elastic object is directly

proportional to the force applied to it”

Increase in length

P2.3: Work, Energy and Momentum

Energy and Work

When an object is moved by a force we say work is done on the object by the force.

The force transfers energy to the object.

Gravitational Potential Energy Transfers

Energy stored in an object because of its position in the Earth’s gravitational field.

The equation:

change of GPE = weight x change in heightjoules, J newtons, N metres, m

change of GPE = weight x change in heightjoules, J newtons, N metres, m

You won’t always be given a weight. Sometimes you will need to use this equation:

joules, J

kilograms, kg

newtons per kilogram, N/kg

metres, m

Kinetic Energy

Kinetic energy mass½ speed2xx=

joules, J kg½ (m/s)2xx=

Kinetic energy

1. If an object of mass 15kg is travelling at 5m/s, how much kinetic energy does it have?

2.A car is travelling at 30m/s and has kinetic energy of 450kJ, what is its mass?

3. A tennis ball has a mass of 0.06kg and has kinetic energy of 2.94kJ when served, what is its speed?

½ x 15 x 25 = 187.5J

m=2xKE/v2=2x450000/900=1000kg

v=(2KE/m) =(5.88/0.6)=3.13m/s

Momentum

The tendency of an object to keep moving in the same direction.momentum (kg m/s) = mass (kg) x velocity (m/s)

40kg person running at 6m/s?

240 kg m/s

Conservation of Momentum

So long as no external forces are acting on the objects involved, the total momentum stays the same in explosions and collisions.

Conservation of momentum questionTwo trolleys collide and stick together. From the data below, calculate the velocity of the trolleys after the collision.

trolley A trolley Bmass = 3 kg mass = 5 kgvelocity = 8 m/s velocity = -4 m/s

momentum = 24 kg m/s (3 x 8) momentum = -20 kg m/s (5 x -4)

total momentum before collision = 4 kg m/s (24 + -20)

mass after collision = 8 kg (3 + 5)

momentum after collision = 4 kg m/s

velocity after collision = momentum / mass = 0.5 m/s

Investigating momentum

Try these…..• A trolley of mass 4kg moving at 10 m/s collides with a 2 kg

trolley moving in the same direction at a velocity of 4m/s. they separate after the collision and the 4 kg trolley slows to 7m/s. What is the final speed of the other trolley? (hint draw diagrams of momentum before and after)

• a trolleyA of mass 1kg is travelling at 2m/s towards another trolleyB of mass 4kg which is travelling towards it at a velocity of 3m/s. On collision they stick together. What is their final combined velocity and in which direction do they travel together? (care with negatives)

10m/s 2m/s to the left

Explosions and Momentum(mass of A x velocity of A) = - (mass of B x velocity of B)

Changing MomentumCars have crumple zones to increase impact time on collision. If you increase the impact time, it will decrease the impact force.

P2.4: Current Electricity

Van de Graaff

generator

When you rub two different insulated materials against each other they become electrically charged.

This only works for insulated objects.

Charging by Friction

Two charged rods of different materials will attract each other if they have a different charge.

Two rods made of the same material will repel each other due to having the same charge.

Like charges repel: unlike charges attract

Circuit Symbols

V

Battery Cell

FuseResistor

LDR

VoltmeterAmmeter

Variable resistor

DiodeSwitch (open)

Bulb (lamp)

A

Resistance is measured in ohms (Ω)

Ohm’s LawThe current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor. So…

If you double the voltage,

the current also doubles.

Ohmic resistorFilament lamp Diode

The filament lamp does not follow Ohm’s Law. Its resistance increases as the temperature of its filament increases.

The diode has a very high resistance in one direction. This means that current can only flow in the other direction.

Series Circuits

The same current passes through components in series with each other

If the current through the lamps is 0.12A, what is the current through the cell?

0.12A

0.12A0.12A

0.12A

Series CircuitsThe total potential difference of the voltage supply in a series circuit is shared between the components.

If the potential difference of the cell is 1.2V and the potential difference of across one lamp is 0.8V, what is the potential difference across the other lamp?

0.4V

1.2V

0.8V 0.4V

Series Circuits

The total resistance of components in series is equal to the sum of their separate resistances.

What is the total resistance if one lamp in series has a resistance of 2 and the other has a resistance of 3?

5

2 3

Parallel Circuits

The total current through the whole circuit is the sum of the currents through the separate components.

A1

If ammeter A1 reads 0.4A and A2 reads 0.1A, what would A3 read?

0.3A

A2

A3

0.4A

0.1A

0.3A

Parallel Circuits

For components in parallel, the potential difference across each component is the same.

If the potential difference of the cell is 6V, the potential difference across each lamp will also be 6V.

6V

6V

6V

P2.5: Mains Electricity

Direct current

The battery in a torch uses direct current.This means it moves in one direction only.

Direct Current

Alternating CurrentMains electricity uses an alternating current.

This means that the current repeatedly reverses direction.

The UK mains supply being about 230 V.

It has a frequency of 50 Hz (50 hertz), which means it changes direction, and back again, 50 times a second.

Alternating Current

The three-pin plug

The earth wire

Connects any metal case to the earth so any extra charge is taken away to

earth

The live wire

Is connected to the mains 230V supply and brings in the electricity

The neutral wire

Completes the circuit by connecting the plug back to the mains

The case is made from tough plastic or rubber, because these materials are good electrical insulators. The three pins are made from brass, which is a good conductor of electricity

The fuse

This melts breaking the circuit if too much current flows.

You always need to use the fuse closest to the current but above it

The Earth WireMany electrical appliances have metal cases. The earth wire creates a safe route for the current to flow through if the live wire touches the casing.

Some appliances (hairdryers, vacuum cleaners) don’t have an earth wire.

Why?

FusesContain a thin wire which melts if too much current passes through it. We say that it ‘blows’.

The rating is the maximum current that can pass through a fuse before melting the fuse wire.

What would happen if the rating was too large?The fuse won’t blow and the appliance could set on fire.

Circuit BreakersJurassic Park

What are the advantages of using a circuit breaker rather than a fuse?

P2.6: Radioactivity

Atomic Number and Mass Number

U235

92

Mass NumberProtons & Neutrons

Atomic NumberProtons

IsotopesIsotopes are atoms of the same element (same protons & electrons) with different numbers of neutrons.This makes them unstable.

H11 H

21 H

31

Hydrogen Deuterium Tritium

RadioactivitySome substances give out radiation from the nuclei of Their atoms. They are radioactive.

This is because their nuclei are unstable, and they become stable by emitting radiation.

This decay is random and cannot be predicted. It goes on all of the time.

We will watch the video twice. Use the information to complete your sheet.

Am24195

Americium

Np23793

Neptunium

The nucleus loses 2 protons and2 neutrons as an

alpha particle

He42

α particle

+

Alpha decay

When an unstable nucleus emits an particle its atomic number goes down by 2 and its mass number by 4.

Beta Decay

C146

Carbon

N147

Nitrogen

e0-1

β particle

+

A neutron changes into a proton. An electron is created and is

emitted.

When an unstable nucleus emits a particle its atomic number goes up by 1 but its mass number stays the same.

Gamma Radiation• Is not a particle

• It is a form of electromagnetic radiation emitted when an atom goes through or decay.

• It has no charge or mass (unlike and radiation)

The Plum Pudding ModelScientists used to think that the atom was a sphere of positive charge with negatively charged electrons dotted around inside it… like plums in a pudding.

One man made it his mission to find out the truth…

Ernest RutherfordErnest Rutherford designed an experiment to test the plum pudding model.

It was carried out by his assistants Hans Geiger and Ernest Marsden.

The results of Geiger and Marsden’s experiment were:

Geiger and Marsden’s gold foil experiment

The experiment was carried out in a vacuum, so deflection of the alpha particles must have been due to the gold foil.

1. Most alpha particles went straight through the gold foil, without any deflection.

2. Some alpha particles were slightly deflected by the gold foil.

3. A few alpha particles were bounced back from the gold foil.

How can these results be explained in terms of atoms?

What stops radiation?We can use a Geiger counter to find out which materials stop, or absorb, radiation.

What could affect our results?

Background radiation! So we measure the background count rate first, then we measure the radioactive material and take away the background count rate.

What stops radiation?Type of radiation Range in the air Absorbed (stopped) by

Alpha () About 5 cm

Paper

Beta () About 1 m Aluminium sheet (5mm thick)Lead sheet (2-3mm thick)

Gamma () Unlimited Lead sheet (several cm

thick)Concrete (more than 1m thick)

IonisationRadiation can knock electrons out of atoms.This causes the atoms to become charged.This is called ionisation.

Why?

+++

+Alpha

particle

IonisationThis can damage or kill a living cell.If the DNA in a cell is damaged, this can also be passed on when the cell generates more cells.

Alpha radiation is actually more dangerous than gamma and alpha radiation. Why?

Incoming radiation

Deflecting Radiation

Using a magnetic field

Half lifeThe decay of radioactive isotopes can be used to measure a material’s age. The HALF-LIFE of an atom is the time taken for HALF of the radioactive isotopes in a sample to decay…

At start there are 16 radioactive isotopes

After 1 half life half have decayed (that’s 8)

After 3 half lives another 2 have decayed (14 altogether)

After 2 half lives another half have decayed (12 altogether)

= radioactive isotope = new atom formed

Using half-life to date a sampleHalf-life can be used to do many useful calculations.

For example, the half-life of carbon-14 is 5,700 years. If a fossil bone has a count of 25, and a piece of bone from a living body has a count of 200, how old is the fossil?

After one half-life, the count will decrease by half to 100.

Three half-lives of carbon-14 have passed, so 3 x 5,700 years makes the fossil 17,100 years old.

After the second half-life, the count decreases by half again to 50.

After the third half-life, the count decreases to 25.

P2.7: Fission & Fusion

Nuclear Fission

A Nuclear Reactor

Fission neutrons are slowed down by atoms in the water molecules.Moderator

Control rods absorb surplus neutrons to keep the reaction under control. Cadmium and boron are commonly used.

Water acts as a coolant. Its molecules gain kinetic energy from the neutrons and the fuel rods.

The reactor core is made form thick steel and enclosed by concrete, which absorb escaped radiation.

Nuclear Fusion

Nuclear FusionWhat you need to know:

Nuclear fusion is the joining of two small nuclei and this process releases energy.

The Sun releases energy due to the fusion of hydrogen isotopes.

Nuclear fusion reactors are difficult to build because they need to work at very high temperatures and high pressures.

The Universe

smallest biggest

The Moon Earth The SunJupiter Milky Way Galaxy The Universe

The Lifecycle of a Star

The End!Good luck