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AQA P2 Physics Booster
2012 Specification
E Ralls
P2.1: Motion
Speed = Distance ÷ Time
This will not be on your data sheet
Distance – time graphs
Speed vs. Velocity
Speed is simply how fast you are travelling…
This car is travelling at a speed of 20m/s
Velocity is “speed in a given direction”…
This car is travelling at a velocity of 20m/s
east
Velocity-time graphs
80
60
constant speed/velocity
decelerating
Velocity
m/s
40
accelerating
20
accelerating
0
10
20
30
Time (s)
40
50
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 equal
and 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
40N
60N
20N
Acceleration
The 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.
Resultant Force 3N
Wind 2N
Engine 4N
Air resistance 3N
Braking Force
The 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 Mass
Mass
Weight
= the quantity of matter in an object
= the force of gravity on an object
The gravitational field strength
of Earth is about
10N/kg
Weight and Mass
Air Resistance
Elastic Potential Energy
An 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.
Hooke’s Law
“The extension of an elastic object is directly
proportional to the force applied to it”
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 height
joules, J
newtons, N
metres, m
change of GPE
joules, J
=
weight
x
newtons, N
change in height
metres, m
You won’t always be given a weight.
Sometimes you will need to use this equation:
kilograms, kg
joules, J
metres, m
newtons per kilogram, N/kg
Kinetic Energy
Momentum
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.
Explosions and Momentum
(mass of A x velocity of A) = - (mass of B x velocity of
Changing Momentum
Cars 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
Charging by Friction
When you rub two
different insulated
materials against each
other they become
electrically charged.
This only works for
insulated objects.
Like charges repel: unlike charges
attract
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.
Circuit Symbols
Battery
Cell
A
Bulb (lamp)
Ammeter
Variable resistor
V
Voltmeter
Switch (open)
Diode
LDR
Fuse
Resistor
Resistance is measured in ohms (Ω)
Ohm’s Law
The 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.
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.
Filament lamp
Ohmic resistor
Diode
Series Circuits
The same current passes through components
in series with each other
0.12A
0.12A
If the current through the
lamps is 0.12A, what is
the current through the
cell?
0.12A
0.12A
Series Circuits
The total potential difference of the voltage
supply in a series circuit is shared between the
components.
1.2V
0.8V
0.4V
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
Series Circuits
The total resistance of components in series is
equal to the sum of their separate resistances.
2
3
What is the total
resistance if one lamp in
series has a resistance of
2 and the other has a
resistance of 3?
5
Parallel Circuits
The total current through the whole circuit is
the sum of the currents through the separate
components.
0.4A
A1
A2
If ammeter A1 reads 0.4A
and A2 reads 0.1A, what
would A3 read?
0.1A
0.3A
A3
0.3A
Parallel Circuits
For components in parallel, the potential
difference across each component is the same.
6V
6V
6V
If the potential difference
of the cell is 6V, the
potential difference across
each lamp will also be 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 Current
Mains 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
Many 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?
Fuses
Contain 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 Breakers
What are
the
advantag
es of using
a circuit
breaker
rather than
a fuse?
Jurassic Park
P2.6: Radioactivity
Atomic Number and Mass Number
Mass Number
Protons & Neutrons
Atomic Number
Protons
235
92
U
Isotopes
Isotopes are atoms of the
same element (same protons
& electrons) with different
numbers of neutrons.
This makes them unstable.
Radioactivity
Some 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.
 Alpha decay
The nucleus loses
2 protons and
2 neutrons as an
alpha particle
When an unstable nucleus emits an  particle its atomic
number goes down by 2 and its mass number by 4.

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 Model
Scientists 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 Rutherford
Ernest Rutherford designed an experiment to test
the plum pudding model.
It was carried out by his assistants
Hans Geiger and Ernest Marsden.
Geiger and Marsden’s gold foil experiment
The results of Geiger and Marsden’s experiment were:
2. Some alpha particles
were slightly deflected
by the gold foil.
3. A few alpha
particles were
bounced back
from the gold foil.
1. Most alpha particles
went straight through
the gold foil, without
any deflection.
The experiment was carried out in a vacuum, so deflection of the alpha
particles must have been due to 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)
Ionisation
Radiation can knock electrons out of atoms.
This causes the atoms to become charged.
This is called ionisation.
+ +
+
+
Alpha
particle
Ionisation
This 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 life
The 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…
= radioactive isotope
At start there
are 16
radioactive
isotopes
After 1 half life
half have
decayed (that’s
8)
= new atom formed
After 2 half lives
another half
have decayed
(12 altogether)
After 3 half lives
another 2 have
decayed (14
altogether)
Using half-life to date a sample
Half-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.
 After the second half-life, the count decreases by half again to 50.
 After the third half-life, the count decreases to 25.
 Three half-lives of carbon-14 have passed, so 3 x 5,700 years makes
the fossil 17,100 years old.
P2.7: Fission & Fusion
Nuclear Fission
A Nuclear Reactor
Control rods absorb surplus neutrons to keep
the reaction under control. Cadmium and
boron are commonly used.
Fission
neutrons are
slowed down
by atoms in
the water
molecules.
Moderator
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 Fusion
What 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
The Moon
biggest
Earth
Jupiter
The Sun
Milky Way Galaxy
The Universe
The Lifecycle of a Star
The End!
Good luck