AQA - GCSE Physics Revision. Additional Physics (P2). Chapter 1 - Motion. What you need to know: Distance-time Graphs Finding out when an object is stationary Finding out when an object is moving at a constant speed Velocity and Acceleration The difference between speed and velocity
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AQA - GCSE Physics Revision
Additional Physics (P2)
A Constant Speed: An object moving at the same speed travels the same distance every second
Speed on a distance time graph is represented by the slope
Speed 1 = fast moving object (steep line)
Speed 2 = steady moving object (straight sloped line)
Speed 3 = stationary object (horizontal line)
Distance Travelled = area under velocity-time graph
Acceleration and Deceleration = gradient of the lines
Finding the area under the graph
Break the area under the graph up into sections and work out the area of separate shapes
Once you have worked out the area of each shape add them together
*If you are only finding out the acceleration or deceleration you only need to work out the gradient of the sloping line (so only one triangle) Deceleration = -distance / time*
How fast = Velocity
How far = Distance
How quickly the velocity changes = acceleration
Object moving at a constant speed = an increased distance
Deceleration on a distance time graph
Upthrust
Forces can:
Twist
Pull
Push
Forces are measured in Newtons (N)
They act in pairs
Each force acts in a certain direction
When two forces interact with each other they always exert equal and opposite forces on each other
Friction
Thrust
Weight/Gravity
Resultant Force: working out the effect each force has on an object. This force has the same effect as all the forces acting on the object
Force
F
Resultant Force (N) = Mass (kg) x Acceleration (m/s²)
M
A
Mass
Acceleration
Thinking Distance: distance travelled by the vehicle in the time taken for the driver to react
Braking Distance: distance the vehicle travels under the breaking force
Stopping Distance = Thinking Distance +Braking Distance
Affect Thinking Distance
Affect Breaking Distance
Weight: the force of gravity upon an object (N)
Mass: the quantity of matter in it (kg)
The Earths gravitational field strength is 10 N/kg
Weight (N) = Mass (kg) x Gravitational Field Strength (N/kg))
Workdone: when an object is moved by force we say that work is done to the object
It can also be the energy transferred/change in gravitational potential energy
Work Done
Gravitational Potential Energy
Work Done/Energy Transferred (J) = Force (N) x Distance (M)
W
G
F
W
D
H
Force
Weight
Height
Distance
Change of Gravitational Potential Energy(J) = Weight (N) x Change in Height (M)
Elastic Potential Energy: the energy stored in a elastic object when work is done on the object
Kinetic Energy (J) = ½ [Mass (Kg) x Speed²(m/s)]
KE = ½ mv²
Momentum: the ability for an object to keep moving (relating its mass and velocity) in the same direction
Mass in motion
Momentum
It is difficult to change the direction of movement of an object with a lot of momentum
Momentum is conserved whenever objects interact, as long as no external forces act on them
P
M
V
Mass
Velocity
The momentum of a moving object(Kg m/s) = Mass (Kg) x Velocity (m/s)
Momentum has a size and a direction
When two objects push each other apart, they move apart with equal and opposite momentum
(Momentum of A) = -(Momentum of B)
OR
(Mass of A x Velocity of A) = -(Mass of B x Velocity of B)
As it is travelling in the opposite direction
Changing Momentumm
The more time an impact takes, the less force is exerted
In the exam they will say which insulator carry’s which charge, unless it specifies which type of rod is being used (here you need to know which insulator transfers electrons)
Electrical Current: the rate of the flow of charge
Discharging an Object
To discharge an object you have to provide a path between the conductor and the ground
The path between the object and the ground allows the electrons to flow to the ground – this object is then Earthed
(Shown in the diagram below)
If it is not insulated from the ground, it wont hold charge as electrons transfer between the conductor and the ground
Sparks and Strikes
If a metal object (conductor) gains to much charge it will produce a spark between the conductor and the charged object
This is because the voltage between the conductor and the ground increase
Lighting is an example of this
A component diagram shows how the components in a circuit are connected together
Every component has its own symbol. The ones on this slide and the next are the ones you need for GCSE
Resistance (ohms) = Potential difference (volts)
Current (amperes)
Ammeter: connected in series with the lamp to measure the current going through the lamp
The current through a resistor of a constant temperature is directly proportional to the potential difference across the resistor
Voltmeter: connected in parallel to measure the potential difference across the lamp
The current is the same through all components in series with each other
The total potential difference/ the voltage supply in a series circuit is shared between
the components
The total potential difference/ the voltage supply of the cells is the sum of the
potential difference/ the voltage of each cell
The total resistance and the components in series is the sum of their separate
resistances
The total current through the whole circuit is the sum of the currents through the separate components
For components in parallel, the potential difference/ the voltage across each component is the same
The bigger the resistance of a component the smaller the current
Alternating Current: a current which repeatedly reverses in direction
You can measure the alternating potential difference using an oscilloscope
You can also see the peak potential difference as well as the frequency of an alternating current (Higher)
Frequency = 1
Time (sec)
In the UK the frequency of mains electricity is 50 cycles per second (50hz)
Mains electricity uses an alternating current
In a mains circuit there is a live wire which is alternately positive and negative every cycle and a neutral wire which is always at 0 volts
Live Wire – is brown and connected to the live pin
The pins in a plug are made of brass
Earth Wire – is yellow and green and connected to the earth pin (a two core cable does not have a earth wire) which is the longest pin in the plug
Neutral– is blue and connected to the neutral pin
The case of the plug is made out of stiff plastic
The cable is copper but is surrounded by an insulator such as rubber/flexible plastic
Earth wires are essential for appliances with metal cases. If the live wire becomes loose and touches the metal case a large current flows to earth, blowing the fuse and breaking the circuit
The fuse sits next to the live wire
A fuse is a safety device which breaks the circuit if the current becomes to high
It contains a thin wire which melts (breaking the circuit)
It is important that you use the correct amp fuse in your appliance.
If a larger fuse in used, the fuse will not blow when it is supposed to and the heating effect on the appliance could result in the appliance catching alight
Circuit Breakers
A circuit breaker is an electromagnetic switch that cuts the current off is the current is too great
After being used it can be reset
Circuit breakers work faster the fuses and are sometimes fitted into ‘fuse boxes’ to replace fuses
Power: energy transferred per second
The power (watts) is the energy transformed (joules) every second, using the equation below:
Power (W) = Energy (J)
Time (S)
E
P
We can also calculate power dissipated (lost) in a device, using the equation below:
P
V
T
I
Power (W) = Current (A) x Voltage (V)
Current
Electrical Current: the rate of flow of charge (measured in Coulomb [C])
The charge of an appliance can be calculated using the equation below:
Charge Flow (C) = Current (A) x Time (S)
Current
C
E
C
T
V
I
We can calculate the energy transformed using the equation below:
Energy Transformed (J) = Potential Difference (V) x Charge Flow (C)
Alpha particles have 2 protons and 2 neutrons
An unstable particle becomes more stable by emitting an α particle
4
0
α
β
2
-1
Neutron changes into a proton (neutron lost = proton gained)
Electrons is created and emitted
Gamma radiation (which has no mass) is also given off by unstable nuclei after alpha and beta radiation is given off
1914 the nucleus was discovered
Alpha particles in a beam are sometimes scattered through large angles when they are directed at a thin metal foil e.g. gold foil
The paths the α particles take
Nuclear Fission: the splitting of an atomic nucleus
Both used in making nuclear weapons
Nuclear Reactor
Nuclear Fusion: when two nuclei are forced close enough together so they form a single larger nucleus
Inside Fusion Reactors
The gas is heated by passing an electric current through it
The gas becomes so hot is forms a plasma of nuclei
The plasma is contained using a magnetic field to prevent it from touching the container walls
When hydrogen nuclei are fused together, helium is formed
Energy is required to make nuclear fusion occur
Energy is also released when two nuclei are fused together (which could be used to produce electricity)
Fusion reactors need to be at very high temperatures before nuclear fusion can take place
Fusion takes place in the sun, as the core is so hot it consists of nuclei without electrons resulting in them fusing together when they collide with enough kinetic energy otherwise they will repel each other