Physics Additional Science

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Distance-time graphs

  • The steeper the line the greater the speed
  • Speed = distance/time
  • The unit for speed is meters per second
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Velocity and acceleration

  • Velocity is speed in a given direction
  • Acceleration is change in velocity per second
  • Acceleration = chnage in velocity/time taken for change
  • A body travelling at a steady speed is accelerating is the direction is changing
  • The slope of the line on a velocity-time graph represents acceleration
  • The area under the line represents the distance travelled
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Forces between objects

  • Fource is measured in zero
  • When two objects interact they always exert equal and opposite forces on each other
  • The resultant force is the single force that would have the same effect on the objects as all the original forces
  • When the resultant force is zero the object will continue how it was before
  • When the resultant force is not zero it will accelerate in the direction of the resultant force
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Force and accleration

  • Resultant force = mass x acceleration
  • The greater the resultant force the greater its acceleration
  • The bigger the mass of the object the bigger the force needed to give it a particular acceleration
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On the road

  • The thinking distance is the distance travelled before the driver reacts
  • The braking distance is the distance travelled whilst the brakes are on
  • The stopping distance = thinking + braking
  • Thinking distance gets increased by drugs and alcohol
  • Braking distance gets increased by the condition of the road, wheels and the weather
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Falling objects

  • Weight = mass x acceleration due to gravity
  • If an objects is on the earth and falling you use the equation:
  • weight = mass x gravitational field strength
  • The weight of an objects is the force of gravity acting on it
  • An object falling freely towards the earth accelerates at about ten meters per second squared
  • When the resultant force becomes equal to the weight of the objects the resultant force is zero. The objects stops accelerating and moves at a constant velocity, its terminal velocity
  • You can only have a terminal veolicty when the object is falling through a fluid
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Energy and work

  • When a force moves an object energy is transferred and work is done
  • The work done is equal to the energy transferred
  • Wrok done = force x distance moved in the direction of the force
  • When work is done against frictional forces the energy supplied is mainly transferred in to heat
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Kinetic energy

  • Elastic potential energy is the energy stored in an elastic object when work is done on the object
  • Kinetic energy is the energy of momentum
  • The kinetic energy of an object depends on its mass and speed
  • Kinetic energy = 1/2 mass x (speed squared)
  • The unit for kinetic energy is joules
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  • All moving objects have momentum
  • Momentum = mass x velocity
  • The unit for momentum is kgm/s
  • Momentum is conserved whenever objects interact, as long as no external forces are acting on them
  • The interaction could be caused be a collision or explosion
  • The objects may move together or apart
  • Momentum has size and direction
  • When objects interact one is positive and one is negative
  • When two objects push each other apart they move apart with equal and opposite momentum
  • The total momentum before an explosion is usualy zero so the momentum after is zero aswell
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Changing momentum

  • force = change in momentum/time taken for change
  • The longer the time taken for the change of momentum the smaller the impact
  • As impact time increases the force becomes less
  • Crumple zones are designed to fold in a collision to increase impact time
  • An air bag is another saftey feature of a car that is designed to do the same thing
  • Impluse = force x time taken to change momentum
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Electrical charges

  • When two electrically insulating materials are rubbed together electrons are rubbed off one material and deposited on the other
  • The way electrons are transferred depends on the particular materials used
  • Like charges repel
  • Unlike charges attract
  • Insulating materials that loose electrons when rubbed become positively charged
  • The bigger the distance between the objects the weaker the force
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Charge on the move

  • Electric current is the rate of flow of charge
  • In a solid conductor the charge carries the electrons
  • Metals are good conductors because they contain free electrons that are not confined to a single atom
  • A metal objects can only hold charge is it is isolated from the ground
  • Otherwise electronss will flow to or from the Earth and discharge it
  • A metal object has ot be earthed by connecting it to the ground
  • The bigger the charge the higher the potential differnce between the object and the Earth
  • If the potential difference becomes high enough a spark may jump across the gap between the object and the earthed conductor brought near it
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Uses and dangers of static electricty

  • A spark from a charged object can make powder grains or certain gases explode
  • Static electricty is used in an electrostatic paint sprayer by:
  • The spray nozzel is connected to a positive terminal
  • As the paint droplets pass through it they pick up a positive charge
  • The paint droplets repel each other so the spread out
  • The item that is going to be painted is connected to a negative terminal so the positively charged droplets are attracted
  • The filler pipes on fuel tanks are earthed to prevent a static charge building up in the pipe which could lead to a spark
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Electric circuits

  • Cell: pushes electrons around a complete circuit
  • Battery: consists of two or more cells
  • Switch: enables the current to be switched on or off
  • Light bulb: emits light as a signal when a current passes through it
  • Diode: allows current through in only one direction
  • Ammeter: measures an electric current
  • Fixed resistor: limits the current in a circuit
  • Variable resistor: allows the current to be varied
  • Fuse: is designed to melt and therefore break the circuit if the current is greater than a certain amount
  • Heater: designed to transform electrical energy in to heat
  • Voltmeter: used to measure the potential difference (voltage)
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  • Resistance = potential difference/current
  • Resistance is measured in ohms
  • The current through a resistor at a constant tempreture os directly proportional to the potential differnence across the reistor
  • Resistance is the oppostion to current flow
  • In a filament lamp the reistnace increases as the tempreture of the filament lamp increases
  • In a diode the forward resistance is low and the reverse resistance is high
  • In a thermister the resitance decreases as the tempreture increases
  • In an LDR the resistance decreases if the light intensity on it increases
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Series circuit

  • The components are connected one after the other
  • If there is a break in the circuit the charge will stop
  • The current is the same in each component
  • The potential difference across each component add up to give the total potential difference
  • The resistors add up to give the total resistance
  • The bigger the resistance of a component the bigger its share of the supply potential difference
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Parallel circuits

  • Each component is connected across the supply
  • If there is a break in one part the chrage can still flow in other parts
  • The potential difference is the same across each component
  • The total current is the sum of the currents through each component
  • The bigger the resistance of a component the smaller its currrent is
  • The current through each component depends on its resistance
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Alternating current

  • Cells and batteries supply current that passes round the circuit in one direction, the direct current
  • The mains supplys a current that changes its direction, the alternating current
  • The UK mains supply is fifty hertz which means it alternates fifty times a second
  • The voltage of the mains in 230 volts
  • The mains circuit has a live wire which alternates between postive and negative potential
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Cables and plugs

  • The outer cover is made out of plastic or rubber as these are good insulators
  • The pins are made out of brass becasue it is a good conductor and it is hard and will not rust or oxidise
  • The nuetral wire is blue and it is connected to the neutral pin
  • The live wire is brown and it is connected to the live pin
  • The earth wire is green and yellow and is connected to the earth pin
  • Appliances with a metal case must be earthed to prevent someone being given a shock if it becomes live
  • Appliances with plastic cases do not need to be earthed because they are insulators
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  • Appliances must be earthed becuase otherwise if a fault develops and the live wire touches the metal case it will become live
  • If a fault develops on a earthed appliance a large amount of current flows to the earth and melts the fuse, disconecting the supply
  • A fuse contains a thin wire that heats up and melts cutting of the current
  • A fuse must be put near the live wire so that if it melts it cuts of the current
  • The rating of the fuse must be slightly higher that the normal current
  • A circuit breaker is an electromagnectic switch that opens and cuts off the supply is the current is bigger than a certain value
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Electrical powere and potential differernce

  • An electrical device tranforms electrical energy in to other forms
  • An electrical deices transfers energy from one place to another
  • This is called the power
  • Power = energy transformed/time
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Electrical energy and charge

  • An electric current is the rate of flow of charge
  • When charge flows through a resistor electrical energy is transformed in to heat
  • Energy transformed = potential difference x charge
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Nuclear reactions

  • Background radiation is the radiation that is around us at all times
  • When a nucleus emits a alpha particle the atomuc number goes down by two and the mass number goes down by four
  • When a nucleus emits a beta particle the atomic number goes up by one and the mass number is unchanged
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The discovery of the necleus

  • Rutherford divised an alpha particle scattering experiment in whcih he fired alpha particles at a piece of thin gold fire
  • Most of the alph particles passed straight through which showed most of the atom was an empty space
  • Some were deflected through small angles showing the nucleus had a postive charge
  • A few rebounded trhough very large angles suggesting the nucleus has a large mass and a very large positive charge
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Nuclear fission

  • Is the splitting of atomic particles
  • The two fissionable isotopes are uranium-235 and plutonium- 239
  • Naturally occuring uranium-238 is non-fissionable so they use enriched unranium that contains 2-3% uranium-235
  • For fission to occur the uranium and plutonium must absorb a neutron
  • The necleus then splits in to two smaller nuclei and two or three nuetrons and energy are released
  • The nuetrons go on to produce futher fissions causing a chain reaction
  • In a nuclear reactor the process is controlled
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Nuclear fussion

  • It is the joining of two atomic nuclei to form a single, larger nucleus
  • During the process fussion energy is released
  • Nuclei approaching each other will repel one another due to their positive charge
  • To overcome this the nuclei must be heated to very high tempretures
  • This gives them enough energy to overcome the repulsion and fure
  • The reaction has to take place in a contained magnetic field
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Ann kirabo

Hey Nina,

Thankyou, this is very helpful.



This is very useful stuff, thanks!

umar rafiq

gud stuff, will come handy

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