Physics 2a + 2b

Velocity and Distance-Time Graphs
1. Velocity and Speed
  1. Speed
    1. How fast you are going
      1. e.g. 30mph
  2. Velocity
    1. How fast you are going in a direction
      1. e.g. 30mph North
2. Distance-Time Graph
  1. Important Notes
    1. Gradient=Speed
    2. Flat=Stationary
    3. Straight up or down=travelling at a steady speed
    4. Steeper=Faster
    5. Downhill=back to starting point
    6. Curves=Acceleration or Deceleration
      1. Steepening curve=Speeding up
      2. Levelling off curve=slowing down
  2. Calculating speed
    1. Speed = Gradient = Vertical/Horizontal = 500/30 = 16.7m/s
Acceleration and Velocity-Time Graphs
1. Acceleration
  1. it is how quickly your velocity is changing
2. Velocity-Time Graphs
  1. Flat sections= Steady Speed
  2. Steeper=More de/acceleration
Wieght, Mass and Gravity
1. Gravity
  1. The force that pulls masses together
  2. Only noticeable when the masses are really really big
2. Weight
  1. The force of gravity pulling it towards the earth
3. Mass
  1. Mass is the amount of stuff
Resultant Forces
1. The resultant force is the overall force on a point or object
2. If you have a number of forces acting on a point or object you can replace them with a single force
  1. As long as they are parallel and act in the same or opposite direction you can swap it for one force
    1. by just addind or subtracting them
      1. The overall force you get is the resulting force
Forces and Accceleration
1. If the resultant force of a stationary object is 0, then the object will remain stationary
2. For a object to remain at a constant speed then the resultant force must be 0
3. If there is a non-zero resultant force then the object will be accelerating or decelerating
4. Formula
  1. F = ma or a = F/m
    1. m = mass kg
    2. a = acceleration m/s2
    3. F = the resultant force N
5. When two objects interact, the forces they exert on each other are equal and opposite
Frictional Force and Terminal Velocity
1. You get friction between two surfaces in contact or when an object passes through liquid
2. Friction slows things down
3. Drag increases as speed increases
4. the faster the object moves at the more friction it has resisting it
5. Objects falling through fluids reach a terminal velocity
6. when an object falls it will accelerate until the frictional force is equal to the accelerating force so it will fall at a steady speed
Stopping Distances
1. Stopping Distance = thinking distance + Braking Distance
2. Thinking Distance
  1. 2 Factors
    1. Speed
    2. Dopiness
      1. Drugs
      2. Alcohol
      3. tiredness
3. Braking Distance
  1. 4 Factors
    1. Speed
    2. Quality of Brakes
    3. Tires + Road surface
      1. Tread Depth
      2. Water
      3. Oil Spillages
    4. Grip
      1. Road Surface
      2. Weather
      3. Tyres
Work and Potential Energy
1. When a force moves an object through a distance, Energy is transferred and work done.
2. Gravitational potential energy
  1. Gravitational Potential Energy = mass x g x height
  2. Gravitational potential energy is the energy that an object has because of its vertical position in a gravitational field
Kinetic Energy
1. K E = 1/2 x mass x speed2
2. Anything that is moving has K E
3. Due to the law of the conservation of energy
  1. When a car is moving the kinetic energy is transferred to heat energy when breaking
    1. Kinetic energy transferred = work done by brakes
      1. 1/2 x mass x speed2 = F x D
Forces and Elasticity
1. Work done to an elastic object is stored as elastic potential energy
2. Extension of an elastic object is directly proportional to force.
  1. This stops working when the force is great enough
    1. There is a limit to the amount of force you can apply to an object for the extension to keep on increasing proportionally
3. F = k x E
Power
1. Power is the rate of doing work - I.E. How much per second
2. P = Work done / Time taken
3. Measured in Watts
  1. 1 watt = 1 joule transferred per min
Momentum and Collisions
1. Momentum = mass x Velocity
2. conservation of momentum
  1. Momentum before = Momentum After
3. Forces cause changes in momentum
4. The larger the force the faster the change in momentum
5. Cars are designed to slow down slower in a crash so that the forces are smaller on the human body.
Car Design and Safety
1. Brakes
  1. Brakes do work against the k e of the car.
  2. Regenerative brakes convert the heat energy from the brakes to electrical energy which is stored chemical energy
2. Cars are designed to convert kinetic energy safely in a crash
  1. Crumple Zones
    1. Car body changes shape at front and rear in a crash
  2. Side Impact bars
    1. Metal tubes in side of car
    2. They help to divert the energy away from the passengers towards other parts of the car.
  3. Seat Belts
    1. Around passengers body
    2. stretch slightly to increase time for passenger to stop.
  4. Air Bags
    1. stop you from hitting hard surfaces
  5. Power Ratings
    1. the higher the engine power the higher the power rating
Static Electricity
1. The build up of static electricity is caused by friction
2. When certain insulating materials are rubbed together - charged electrons will be rubbed off and dumped on the other
3. It is ONLY the electrons that move -
4. Like charges repel, Opposite charges attract.
5. Charges can move easily through conductors - metals
Current and Potential Difference
1. P.D = the driving forces that pushes the current round . Volts
2. the greater the resistance across a component, the smaller the current that flows.
3. Total charge through a circuit depends on current and time
  1. Current = charge/Time
4. P.D is the Work Done per unit charge
  1. P.D = Work Done / Charge
Circuits - The Basics
1. Ammeter
  1. Measures current
  2. Must be in Series
2. Voltmeter
  1. Measures P.D - Voltage
  2. Must be in parallel
Resistance
1. Resistance increases on tempreture
2. The longer the wire the more resistance
3. The smaller the diameter of the wire the more resistance
4. P.D = Current x Resistance
Circuit Devices
1. Diodes
  1. 1 way
2. LED
  1. Emits light when a current flows through in a forward direction
3. LDR
  1. More light less resistance
4. Thermistor
  1. As temp increases resistance decreases
Series Circuits
1. All connected in a line
2. P.D is shared
3. Current is the same everywhere
4. Resistance adds up
Parralel Circuits
1. Separately connected to the supply
2. P.D is the same across all components
3. Current is shared between branches
Series and parallel circuits
1. Series Circuit - Example
  1. Christmas Trees lights
2. Parallel Circuit - Example
  1. Cars electrics
Mains electricity
1. Mains supply is AC battery supply is DC
2. The UK mains supply is approximately 230 volts
3. It is a Alternating current, which means it is constantly changing direction
4. Electricity supplies can be shown on a oscilloscope
5. on a oscilloscope a AC current will be a wave and DC will be a straight line
6. Th e vertical height of AC is the input voltage
7. On DC, the distance from the centre line to the trace is the voltage
Electricity in the home
1. Hazards
  1. Long Cables
  2. Frayed Cables
  3. Cables in contact with something hot or wet
  4. Water near sockets
    1. Socket overloading
    2. Lighting sockets without bulbs
  5. Shoving things into sockets
  6. Damaged plugs
    1. Appliances without covers on
2. Most cables have three separate wires
  1. The brown LIVE WIRE in a mains supply alternates between the high +VE and -VE VOltage
    1. The blue NEUTRAL WIRE is always at OV. Electricity normally flows in and out through the live and neutral wires only.
      1. The green and yellow wire is the EARTH WIRE. it is for protecting the wiring and for safety
        It works with fuse to prevent fires and shocks
3. Learn the safety features
  1. The right coloured wire is connected to the right pin
  2. No bare wires showing inside the plug
  3. Cable Grip
Fuses and Earthing
1. Earthing and fuses prevent electrical overloads
2. If there is a fault in the circuit, because of the earth it will connect and make the fuse break because the current is too great. This isolates the whole appliance
3. Insulating Materials make appliances "Double Insulated"
  1. Double insulated appliances don't need a earth wire because there is nothing to earth
4. Circuit Breakers have some advantages over fuses
  1. They are the same as fuses but they open a switch instead of break / melt
  2. They also can be reset by a switch which is more convenient than fuses and cheaper
Energy and Power in circuits
1. Energy is transferred from cells and other sources
  1. Anything which supplies electricity is also supplying energy
  2. Kinetic energy = motors
  3. Light energy = lamp
  4. Heat energy = Kettles
  5. Sound energy = speakers
2. All resistors produce heat when a current flows through them.
  1. When an electric current flows through anything with electrical resistance then electrical energy is converted into heat energy
  2. The more current the more heat
  3. The more voltage means more heating
3. If an appliance is efficient it wastes less energy
  1. Appliances that are energy efficient
    1. transfer more of their total electrical energy output to useful energy
4. Power Ratings of appliances
  1. The total energy transferred by an appliance depends on how long the appliance is on and it's power rating. The power of an appliance is the energy that it uses per second
  2. Energy Transferred = Power rating x Time
Power and energy change
1. Electrical Power and Fuse Ratings
  1. Power = current x potential difference (voltage)
    1. Most electrical goods show their power rating and voltage rating. To work out the size of the fuse needed, you need to work out the current that the item will normally use.
2. The Potential Difference is the energy transferred per charge passed
  1. when charge (Q) goes through a change in potential difference (V), then energy(E) is transferred.
    1. Energy is supplied to the charge at the power source to 'raise' it through a potential.
      1. The charge gives this energy when it 'falls' through any potential drop in components elsewhere in the circuit.
        Energy transformed = charge x potential difference
        The bigger the change in PD the more energy is transferred for a given amount of charge passing through a circuit
The Atomic structure - and Rutherford
1. In 1804, John Dalton agreed with democritus that matter was made up of tiny spheres (atoms) that couldnt be broken up
  1. 100 years later J J Thomson discovered that electrons could be removed from atoms
    1. In 1909, Rutherford and Marsden tried firing a beam of alpha particles at a thin sheet of gold foil
      1. They expected that the positively charged alpha particles would be slightly deflected by the electrons in the plum pudding model. However, most of the particles went straight through, but the odd one came straight back at them.
        They realised that most of the mass was in the + charged nucleus
2. Rutherford and Marsden came up with the nuclear model
Atoms and Ionising Radiation
1. Isotopes are different forms of the same element
  1. An isotope has the same amount of protons and electrons, however has a different number of neutrons
2. Radioactiviiy is a totally random process
  1. Radioactive substances give out radiation from the nuclei of their atoms, whatever is done to them.
    1. Radioactive substances spit out one or more of the three types of radiation - alpha, beta and gamma
3. Background radiation comes from many sources
  1. Radioactivity of naturally occurring unstable isotopes which are all around us
    1. Radiation due to man made sources - Nuclear weapons tests, nuclear accidents, dumped nuclear waste.
      1. Radiation from space - cosmic rays
4. Atoms and Ionising Radiation
  1. Alpha particles
    1. they are the same as a helium nucleus, and they are big and heavy and slow moving. Therefore they don't penetrate very far into materials and are stopped quickly, even when travelling through air. Because of their size they are strongly ionising. Which means they bash into a lot of atoms ans knock electrons off them before they slow down, which creates lots of ions.
  2. Beta particles
    1. Beta particles are electrons. They move quite fast and they are quite small (they're electrons). They penetrate moderately into materials before colliding, have a long range in air, and are moderately ionising too. For every Beta particle emitted, a neutron turns to a proton in the nucleus. A B-particle is an electron, with virtually no mass and a charge of -1
  3. Gamma rays
    1. Gamma Rays, are very short wavelength, EM Waves. They are the opposite of alpha particles in a way. They penetrate far into materials without being stopped and pass straight through air. This means they are weekly ionising because they tend to pass through rather than collide with atoms. Eventually they hit something and do damage. Gamma rays have no mass and no charge.
  4. Radiation Dose
    1. The damage caused by radiation depends on the radiation dose
      1. Enter text here
        Radiation dose depends on the type and the amount of radiation.
    2. Radiation Dose depends on location and occupation
      1. Certain underground rocks (e.g. granite) can cause higher levels at the surface, especially if radioactive radon gas is released and it can get trapped in people's houses.
        Nuclear Industry workers and uranium miners are typically exposed to 10 times more radiation than normal. They have to wear hazmat suits to stop them from touching or inhaling radioactive substances. They monitor their doses with badges and check ups.
        Radiographers work in hospitals using ionising radtion and so have a higher risk of radiation exposure. They wear lead aprons and stand behind lead screens to protect them from prolonged exposure to radiation.
        At high altitudes the background radiation is higher because your closer to cosmic rays. Also underground for miners because they're surrounded by rocks.
Half-Life
1. The radioactivity of a sample always decreases over time
2. As a radioactive sample decays it loses more atoms, therefore as it decays it will lose in mass and will emit less radiation
3. The half life of a substance is how long it takes for half of the starting substance to decay.
  1. for example a substance with a half life of 4 years and a starting mass of 10kg will decay to 500g after 4 years.
4. Here is a Half life graph ===>
Uses of radiation
1. Smoke detectors - use alpha radiation
  1. Tracers in Medicine - Always short half life Beta or Gamma emitters
2. Radiotherapy - the treatment of cancer using gamma rays
  1. Sterilisation of food and surgical instruments using gamma rays
Radioactivity safety
1. Radiation harms living cells
  1. Radiation will enter living cells and collide with the molecules
    1. These collisions cause ionisation, which damages or destroys the cells
      1. Lower doses tend to cause minor damage without killing the cell.
        This can give rise to mutant cells which divide uncontrollably, this is called cancer.
        Higher doses kill cells which causes radiation sickness, if a lot of cells get hit all at once
        The severity depends on the exposure, energy and penetration and type of radiation.
        Outside the body Beta and Gamma radiation is the most dangerous
        Inside the body alpha radiation is the most dangerous because it does the most ionising
2. Safety Precautions
  1. 1) use for the shortest time possible
  2. 2) Never allow skin contact with the source
  3. 3) Hold it at arms length, to reduce amount of radiation particles that hit you
  4. 4) Point it away from you
  5. 5) Use lead to store it because it absorbs the radiation
Nuclear Fission and Fusion
1. Nuclear Fission
  1. Nuclear Power stations use nuclear reactors to produce energy
    1. inside, a controlled chain reaction takes place which atomic nuclei split up and release heat energy
      1. The heat, heats water which creates steam which turns a turbine, which generates electricity
2. Nuclear Fussion
  1. It is the joining of small atomic nuclei. Two light nuclei(hydrogen) can join to make a nucleus - this is called fusion.
    1. Fusion creates even more energy than fission. So people are trying to make fusion reactors, and there isn't much waste left behind and there is plenty of hydrogen. The only problem is that it can only happen at really high temperatures - 10 000 000'c
      1. For this you need a extremely strong magnetic field, there are a few experimental reactors around but non of them are generating electricity yet.
3. The chain reactions
  1. For fission, a slow moving neutron must be absorbed into a uranium or plutonium nucleus. This extra neutron makes it unstable, causing it to split. Each time a nucleus splits up it spits out two or three more neutrons, which hit another nucleus causing another split, therefore the chain reaction continues.
  2. Nuclear fission gives out a lot of energy. Nuclear processes give out a lot more energy than chemical processes do e.g. Nukes.
The Life Cycle of stars
1. 1) Protostar - clouds of dust and gas pulled together into spirals by gravity
  1. 2) gravitational energy is converted to heat until nuclear fusion happens, this gives out massive amounts of heat and light. A star is born
    1. 3) Main Sequence Star - The star immediately enters a long stable period. The heat energy creates outward pressure which balances gravity pulling everything inwards. This energy output maintains for millions of years due to the massive amounts of hydrogen, this period lasts for several billions years
      1. 4) Small Star/Red Giant - Eventually the hydrogen begins to run out and heavier elements such as iron are made through the nuclear fusion of hydrogen. As it's a small star it swells into a red giant.
        5) The star then becomes unstable and ejects it's outer layer of dust and gas as a planetary Nebula
        6)This leaves behind a hot dense solid core - a white dwarf, which cools to become a black dwarf and eventually disappears
      2. 4)Large star/Super Red Giant - Eventually the hydrogen begins to run out and heavier elements such as iron are made through the nuclear fusion of hydrogen. As it's a large star it swells into a Super Red Giant.
        5)The star starts to glow brightly again, as they undergo more fusion, they expand and contract several times, forming heavy elements such as iron. Finally they explode to create a Super Nova, forming elements heavier than iron and ejecting them into the universe to form other planets and stars.
        6) The remainders of the super nova is a very dense core called a neutron star. If the star is big enough it will become a black hole.

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	Created by James Squibb about 11 years ago