# P2

physics revision for aqa p2

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P2 Physics
Speed and Velocity
A time-distance graph plots distance travelled against the time taken
A slope on a time-distance graph represents speed, the steeper the slope the
greater the speed
o Speed = distance ÷ time
o Distance = speed x time
o Time = distance ÷ speed
Speed is measured in meters per second (m/s)
Velocity is a speed but with a given direction
This means that if a moving object changes direction then its velocity will change
even if its speed says the same
If the velocity we say the object is accelerating or decelerating
o Acceleration = change in velocity ÷ time taken for the change
Acceleration is measured in meters per second per second (m/s²)
A velocity-time graph plots the velocity against the time taken
The slope on a velocity time graph represents the acceleration or deceleration
The steeper the slope the greater the acceleration or deceleration
The area under the graph represents the distance travelled
We use the gradient of the line to work out the speed of an object, for example if
the graph shows it has moved 10 meters in 2 seconds then its speed is 5m/s
Speeding up and slowing down
We measure force in newtons (N)
Objects always exert equal and opposite forces on each other, these are often
referred to as action and reaction forces
Resultant force is where one single force will have the same effect than all the other
forces put together
When the resulting force is zero it means the object is stationary or is travelling at a
constant speed
If the resulting force is not equal to zero then it means the object is accelerating in
the direction of the resulting force
A resulting force always causes an acceleration, without acceleration the resulting
force must be zero
o Resulting force = mass x acceleration
The greater the resulting force the greater the acceleration
A vehicle travelling at a constant pace has a resulting force of zero which means the
all the driving forces are equal

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The stopping distance is of a vehicle is the distance travelled by the object during the
thinking distance and the breaking distance
The thinking distance is increased if the driver is under the influence of alcohol or
drugs and the braking distance is increased if the road is wet or the brakes are worn
When an object is falling freely, the resulting force acting on it is gravity
o Weight = mass x acceleration due to gravity or,
o weight = mass x gravitational field…read more

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When a force acts on a moving object its momentum changes
Force = change in momentum ÷ time taken
If you increase the time taken then the force exerted decreases e.g. crumple zones
and airbags
Static Electricity
If two insulating materials rub against each other, electrons are rubbed off one
material and deposited on the other
Because electrons have a negative charge, the material which gets the electrons
become negatively charged and the one that loses them becomes positively charged

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Static electricity can be dangerous as well as being very useful
The filler pipes on road tankers that are used to pump fuel into storage tanks are
earthed to prevent them becoming charged because a spark could cause an
explosion
Another way to prevent the dangers of electrostatics is by using antistatic materials
Current Electricity (look at pictures for circuit symbols)
A cell is necessary to push electrons around a complete circuit
A battery consists of two or more cells, increasing the power supply

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Power = current x potential difference
The potential difference of the mains supply is 230 volts so the equation above can
be used to work out what fuse is needed
In a resistor the electrical energy is transferred to heat, the amount of energy that's
transformed can be worked out using the equation below
o Energy = potential difference x charge
A coulomb (C) is the amount of electric charge transported in one second through a
current of 1 amp
o Charge = current x…read more

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In a parallel circuit the current varies with resistance between each
component
Mains electricity
Cells (and battery's) supply a current which only flows in one direction, this is called a
direct current or DC, however if the current from the mains supply passes in one
direction then reverses and passes in the other direction it is called an alternating
current or AC
The frequency of the UK mains electricity is 50Hertz (Hz), this means it is alternating
directions 50 times a second, the voltage is…read more

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Atoms of the same element can also have a different number of neutrons in which
case it is an isotope, only the neutron number and the electron number can change
or it becomes a different element
An alpha particle consists of two protons and two neutrons, this means that when a
nucleus emits an alpha particle, the atomic number decreases by 2 and the mass

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Nuclear fusion is the process of two atomic nuclei joining to form one single, larger
nucleus, during this process energy is released (this is the process in which energy is
released as stars)
The problems with nuclear fusion are the nuclei approaching each other will repel
each other due to their positive charge, to overcome this they are heated to an
extremely high temperature to overcome the repulsion and fuse together, because
of the high temperatures the reaction has to be contained in a magnetic…read more