1. Velocity & Acceleration Physics Fission and fusion
Forces Radioactive decay
Work and Energy Power in electrical appliances
Momentum Mains Electricity
Static Electricity Circuits
Unit 2
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2. Home Next
Velocity & Acceleration
Distance-time graphs:
They show the distance
an object,
e.g. a car has moved in a
certain amount of time.
Videos
Acceleration Part 1
Acceleration Part 2
Speed and Velocity

3. Back
Acceleration= change in velocity (m/s) Next
(m/s²)
Home
time taken for change (s)
Velocity-time graphs
• Velocity is speed in a given direction
• Acceleration is change of velocity
per second
A body travelling at a steady speed is
accelerating if its direction is changing.

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Forces
• Force is measured in newton's (N)
• The force of friction always acts in the opposite direction of
the movement.
• Friction occurs when an object moves through air or water,
when solid objects slide (they heat up and wear away).
• Weight= mass x gravitational field strength
(newton, N) (kilogram, kg) (newton/kilogram, N/kg) Usually 10N/Kg,
unless the question
states otherwise.
Stopping Distance
Stopping distance of a car= braking + thinking distance Remember: You cannot
SLOW down time, you
Depends on the weather Depends on the driver’s
can just INCREASE
conditions (wet/icy roads) reaction time: tiredness,
and the vehicle, (worn drugs, alcohol, and the collision time, INCREASE
brakes/tyres). speed. reaction time etc.

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Resultant force= mass x acceleration
Home (newton, N) (kg) (m/s²)
• A stationary object remains still because the resultant force is zero.
This is because both forces acting on it are balanced.
• E.g. a book is sat on in your hand, the weight of the book
is equivalent to the force your hand is exerting to keep it in place.
Terminal velocity= constant speed
When an object falls through a fluid, the faster it
moves, the greater the force of friction.
When a body falls:
1) At the start, it accelerates (due to the force
of gravity-weight),
2) Frictional forces (e.g. air resistance)
increase …until they balance the
gravitational force,
3) Then the resultant force is zero, and the
body falls at its ‘terminal velocity’.

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Work and Energy
• A moving object also has movement energy, also called kinetic energy.
• When a force moves an object, energy is transferred and work is done:
Work done (joules , J) = energy transferred (joules , J)
Work done (J) = force applied (N) x distance moved in the direction of the force (m)
Kinetic energy= ½ x mass x speed²
Kinetic energy can be transformed into other forms of energy as shown in the table:
Example: K.Energy is
transformed into:
A car braking Heat in brakes + An object has more kinetic
tyres energy:
A wind turbine Electricity, heat, -If it has a bigger mass
sound -If it travels at a higher speed
Rollercoaster car, Gravitational
going up a ramp potential energy Video
(g.p.e), heat Potential & Kinetic Energy

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Momentum
• Momentum has both MAGNITUDE and
DIRECTION.
• ‘Momentum is conserved’ means that the
momentum before=momentum after. i.e. the
total momentum remains the same.
• In a collision, momentum isn’t always
conserved because there are external forces
acting on the colliding objects.
Newtons kgm/s seconds

8. Back In a car crash… Next
• Crumple zones are created to increase collision time,
therefore decreasing the force.
• Seatbelts stretch slightly, increases the time,
decreasing the force acting on the driver.
• Airbags also slow you down more gradually.
Remember always refer to,
‘force= change in momentum ÷ time taken for change’.
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Static Electricity
• Electrostatic precipitators and photocopiers
make use of electrostatic charges.
• When certain materials rub against each other
they become charged.
• The material that gains electrons becomes
negatively charged.
• The material that loses electrons becomes
positively charged.

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Electrostatic Precipitators
Dangers
The more charge put on an object, the higher the
voltage (p.d) between the object and earth. If the
p.d is very high, then a spark can jump between the
object and any earthed conductor.
• Smoke particles pick up a
negative charge.
• Smoke particles are attracted to
the collecting plates.
• Collecting plates are knocked to
remove the smoke particles.

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Preventing fires and explosions
• A liquid flowing through a pipe can become
charged by rubbing. This can be dangerous
because it could cause a spark if the substance is
inflammable.
• Whenever an aeroplane is being refuelled by a
tanker, they are always connected by a copper
wire.
• Friction between the fuel and pipe gains
electrons, charging the fuel and pipe, earthing
the object prevents a spark and explosion.
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12. Back Circuits Next
Home
amps
Resistors in series Resistors in parallel
Light Dependent
Resistor (LDR)
Thermistor
The same current goes through The current is shared
all the components The p.d is equal for both
The p.d across the cell is shared
Resistance= R1 + R2
Voltmeters are
placed parallel
Ammeters are placed
in series

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Mains Electricity
• Frequency of mains supply in UK = 50 Hertz
Alternating Current (a.c) Direct current (d.c)
-Is constantly - Flows in only one direction
changing direction
-As the frequency is 50Hz,
each cycle lasts for 1/50th second
The mains supply in the UK is 230V
The live terminal alternates between a positive and negative voltage with respect to the
neutral terminal.
The neutral terminal stays at a voltage close to 0 with respect to earth.

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The 3 pin plug
Home
The cable has a plastic cover because plastic is a good
insulator.
Copper wires inside the cable are good conductors.
The Earth Wire- for safety
Appliances with metal cases need to be earthed.
The case is connected to the earth pin (by the green/yellow wire).
If a fault connects the case to the live wire, then a large current
flows to earth and melts the fuse.
The fuse:
Must be in the live wire so the appliance becomes disconnected,
Should have a value (rating) higher than (but as close as possible to) the
normal working current,
Can be replaced by a circuit breaker.

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Power in electrical appliances
• Electrical appliances are used to transform electrical
energy to some other useful form of energy.
• This may be light, sound, heat, kinetic energy and many
more.
Power(W)= energy transformed(J) ÷ time taken(s)
Power(W)= current (A) x p.d (V)
Energy Transferred(J)= p.d (V) x charge (Coulomb)
Charge(C)= Current(A) x Time (S)

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Radioactive decay
• Atomic Structure
At one time, scientists believed in a ‘plum pudding’ model of the atom.
They believed that the negative electrons were stuck in a blob of
matter.
Then Rutherford and Marsden fired alpha particles at gold foil (gold
leaf) which scattered them, as shown:
Rutherford had shown that
the atom had a tiny, heavy,
positively charged nucleus.
Science Daily

17. Back Protons +Neutrons = Mass Number Next
Protons = Atomic number
Home Number of Electrons =
Number of Protons
The nucleus is made up of protons AND neutrons, with electrons orbiting.
In a neutral atom, the number of electrons equals the number of protons.
Atoms can gain or lose electrons to become charged particles called ions.
Different elements have a different number of protons (atomic number).
Atoms of the same element can have different number of neutrons but to remain
the same element they have to have the same number of protons.
These are called isotopes.
Lithium can have several numbers of neutrons for
one isotope and less/more in another.
Background radiation
This comes from natural and artificial
sources 

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Radioactive decay…
• Radioactivity occurs as a result of changes in the nuclei of atoms.
• A radioactive isotope is an atom with an unstable nucleus.
• When it splits up (decays):
• It emits alpha, beta or gamma radiation,
• A different atom is formed, with a different number of protons.
In Beta you lose 0 in the mass
and gain 1 proton. So 6
protons turns to 7 protons, 8
neutrons goes to 7 neutrons.
This is why the mass remains
the same number. The proton
has gained one, neutron lost
one.
The new atom has 2 protons (and
neutrons) less than the original
atom= different element.

19. Back Next
Home Fission and Fusion
• In a nuclear power station energy is released
from the nuclei of uranium atoms in a process
called, ‘nuclear fission’. This energy is
transformed into electrical energy.
• When an atom is bombarded with a neutron:
the nucleus may split, ‘fission’ into two
smaller nuclei.
• This can lead to a chain reaction.
Uranium 235 and Plutonium 239 are used in nuclear fission.

20. Back
Fission and Fusion
• Nuclear fusion is the joining of two nuclei, forming a
larger one, e.g. hydrogen -> helium
• The sun is an example of nuclear fusion.
• Nuclear fusion reactors are not used to produce energy
in a nuclear power station because the reaction does
not last long enough and they use more energy than
they produce.
• However, scientists continue to try and develop a
practical fusion reactor because it will give another
source of energy, would not produce any radioactive
waste and want to show that it can be done.
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