Physics (additional)

  • Created by: lilyexall
  • Created on: 26-03-16 08:15


Distance-time graph:

  • Distance-time graph tells you how an object's distance changes over time
  • The gradient represents the speed
  • The steeper the gradient the greater the speed of the object 
  • Flat-line = no moment 
  • Downwards line = returning to starting position 
  • Upwards curve = deceleration 

Speed (m/s)=Distance(m)/Time taken(s) 

Velocity and acceleration:

  • Velocity is the speed in a given direction
  • Acceleration is the change of velocity per second

a = v-u / t 

  • a = acceleration, m/s2
  • v = final velocity, m/s
  • u = initial velocity, m/s
  • t = time taken, s
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Velocity-time graphs;

  • Gradient represents acceleration
  • Steeper gradient = bigger acceleration 
  • Flat (horizontal) line = no acceleration 
  • The area under the line in the graph = distance travelled (Total distance = total area) [H]

Using graphs;

  • If you calculate the gradient of the line on the distance-time graph for an object, the answer will be the speed of an object
  • If you calculate the gradient of the line on a velocity-time graph for an object, the answer will be the acceleration of the object
  • Calculating the area under the line between two times on a velocity-time graph gives the distance travelled between those times 
  • Always use the numbers from the graph scales in any calculations
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Forces between objects;

  • A force can change the shape of an object or change its motion or state of rest
  • The unit of force  = newton (N)
  • When two objects interact they always exert equal and opposite forces on each other

Resultant forces;

  • The resultant forces = a single force that has the same effect as all the forces acting on an object 
  • If an object is accelerating there must be a resultant forces acting on it 
  • If the resultant force is:
  • Zero (balanced) - the object will continue to move at the same speed and same direction 
  • Not Zero (unbalanced) - the object will accelerate in the direction of the resultant (single) force 
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On the road;

  • Friction and air resistance oppose the driving force of a car 
  • The stopping distance depends on the thinking distance and the braking distance 
  • The stopping distance of a vehicle is the distance it travels during the drivers reaction time (thinking distance) plus the distance it travels under the braking force (the braking distance)
  • The thinking distance is increased if the driver is tired or under the influence of drugs or alcohol 
  • The braking distance can be increased by: 1) - Poorly maintained roads or bad weather conditions. 2) - The condition of the car (e.g. Worn tyres or worn brakes)
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Stretching and squashing 

  • The extension is the difference between the length of the spring and its original length
  • Hooke's law - The extension of a spring is directly proportional to the force applied to it, provided the limit of proportionality is not exceeded
  • The spring constant of a spring is the force per unit extension needed to stretch it
  • F = k x e 

Force and speed issues;

  • Fuel economy of road vehicles can be improved by reducing the speed or fitting a wind deflector 
  • Average speed cameras are linked in pairs and they measure the average speed of a vehicle 
  • Anti-skid surfaces increase the friction between a car tyre and the road surface. This reduces skids, or even prevents skids altogether 
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Work, energy and momentum

Energy and work;

  • Work is done on an object when a force makes the object move 
  • Energy transferred = work done 
  • W = F x d 
  • Work done to overcome friction is transferred as energy that heats the objects that rub together and the surroundings

Gravitational potential energy;

  • The gravitational potential energy of an object depends on its weight and how far it moves vertically 
  • Ep = m x g x h 

Kinetic energy;

  • The kenetic energy of a moving object depends in its mass and its speed 
  • Ek = 1/2 x m x V2
  • Elastic potential energy is the energy stored in an elastic object when work is done on the object 
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Work, energy and momentum


  • p = m x v 
  • The unit of momentum is kg m/s
  • Momentum is conserved whenever objects interact, provided no external forces act on them


  • Momentum = mass x velocity
  • When two objects push each other apart, they move apart: 1) With different speeds if they have unequal masses, 2) With equal and opposite momentum so their total momentum is zero.

Impact force;

  • When vehicles collide the force of the impact depends on; mass, change of velocity and the duration of the impact
  • When two vehicles collide: 1) They exert equal and opposite forces on each other, 2) Their total momentum is unchanged. 
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Work, energy and momentum

Car safety;

  • Seat belts and air bags spread the force across the chest and they also increase the impact time 
  • Side impact bars and crumple zones 'give away' in an impact so increasing the impact time 
  • We can use the conservation of momentum to find the speed of a car before an impact 
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Current electricity

Electrical charges;

  • Certain insulating materials become charged when rubbed together
  • Electrons are transferred when objects become charged 
  • Like charges repel; unlike charges attract 

Electric circuit;

  • I = Q / t 
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Current electricity


  • V = W/Q = E/Q
  • R = V/I
  • Ohm's law statues that the current through a resistpr at contant temperature is directly proportional to the protential difference across the resistor
  • Reversing the current through a component reverses the protential difference across it 

More current - protential difference graphs;

  • Filament bulb: resistance increases with increase of the filament temperature 
  • Diode: 'forward' resistance low; 'reverse' resistance high
  • Thermistor: resistance decreases if it temperature increases
  • LDR: resistance decreases if the light intensitiy on it increases 

Series circuit;

  • For components in series; 1) The current is the same in each component, 2) adding the potential differences gives the total protential difference, 3) adding the resistances gives the total resistance  
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Current electricity

Parallel circuits;

  • For components in parallel; 1) The total current in the sum of the currents through the separate component, 2) The bigger the resistance of a component the smaller the current is 
  • In a parallel circuit the potential difference is the same across each component 
  • To calculate the current through a resistor in a parallel circuit use I = V/R
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Mains electricity

Alternating current;

  • Direct current is in one direction only - Alternative current repeatedly reverses its direction
  • The peak voltage of an alternative potential difference is the maximum voltage measured from zero volts 
  • A mains circuit has a live wire that is alternatively positive and negative every cycle and a neutral wire at zero volts. f = 1/T


  • A fuse contains a thin wire that heats up and melts if too much current passes through it. This cuts off the current 
  • A circuit breaker is an electromagnetic switch that opens (i.e. 'trips') and cuts the current pff if too much current passes through it 
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Mains electricity

Cables and plugs;

  • Sockets and plugs are made of stiff plastic materials, which enclose the electrical connections 
  • Cables consist of two or three insulated copper wires surrounded by an outer layer of flexible plastic material
  • In a three-pin plug or a three-core cable: 1) The live wire is brown, 2) The neutral wire is blue, 3) The eath wire is green and yellow
  • The earth wire is used to earth the metal case of a mains appliance 

Electrical power and protential difference;

  • The power supplied to a device is the energy transferred to it each second 
  • P = I x V
  • Correct rating (in amperes) for a fuse = electrical power (watts) / protential difference (volts)
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Mains electricity

Electrical energy and charge;

  • An electric current is the rate of flow of charge
  • Q = I x t 
  • When charge flows through a resistor, energy transferred to the resistor makes it hot 
  • E = V x Q

Electrical issues;

  • Electrical faults are dangerous because they can cause electric shocks and fires
  • Never touch a mains appliance (or plug or socket) with wet hands. Never touch a bare wire or a terminal at a potential of more than 30 V
  • Check cables, plugs and sockets for damage regularly 
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Observing nuclear radiation;

  • A radioactive substance contains unstable nuclei that become stable by emitting radiation
  • There are three main types of radiation from radioactive substances - alpha, beta and gamma radiation
  • Radioactive decay is a random event - we cannot predict or influence when it happens
  • Background radiation is from radioactive substances in the enviroment, or from space, or from devices such as X-ray machines

The discovery of the nucleus;

  • Rutherford used the measurements from alpha particle scattering experiments as evidence that an atom has a small, positively charged, central necleus where most of the mass of the atom is located
  • Most alpha particles passed straight through = most of the atom is atom 
  • Some alpha particles defected through small angles = nucleus has a positive charge
  • Few reflected back = nucleus has a large mass, very positivley charged 
  • The nuclear model of the atom correctly explained why the alpha particles are scattered and why some are scattered through a large angles 
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Radioactivity (incomplete)

Nuclear reactions;

  • Isotopes of an element are atoms with the same number of protons but different number of neutrons. Therefore, they have the same atomic numbers but different mass numbers
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More about alpha, beta and gamma radiation;

  • a-radiation is stopped by paper or a few centimetres of air 
  • B-radiation is stopped by a thin metal or about a metre of air
  • y-radiation is stopped by a thick lead and has an unlimited range in air 
  • A magnetic or an electric field can be used to separate a beam of alpha, beta and gamma radiation 
  • Alpha, beta and gamma radiation ionise substances they pass through


  • The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve
  • The activity of a radioactive source is the number of nuclei that decay per second
  • The number of atoms of a radioactive isotope and the activity both decrease by half every half-life
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Radioactivity at work;

  • The use we can make of a radioactive isotope depends on its half-life, and the type of radiation it gives out 
  • For radioactive dating of a sample, we need a radioactive isotope that is present in the sample which has a half-life about the same as the age of the sample
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Energy from the nucleus

Nuclear fission;

  • Nuclear fission is the splitting of a nucleus into two approximately equal fragments and the release of two or three neutrons 
  • Nuclear fission occurs when a neutron hits a uranium-235 nucleus or a plutonium-239 nucleus and the nucleus splits
  • A chain reaction occurs when neutrons from the fission go on to cause other fission events
  • In a nuclear reactor control rods absorb fission neutrons to ensure that, on average, only one neutron per fission goes on to produce further fission 

Nuclear fusion;

  • Nuclear fusion in the process of forcing two nuclei close enough together so they form a single larger nucleus 
  • Energy is released when two light nuclei are fused together 
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Energy from the nucleus

Nuclear issues;

  • Radon gas is an a-emitting isotope that seeps into houses in certain areas through the ground
  • There are hundreds of fission reactors safely in use throughout the world. None of them are the same type as the Chernobyl reactors that exploded
  • Nuclear waste is stored in safe and secure conditions for many years after unused uranium and plutonium (to be used in the future) is removed from it 

The early universe;

  • A galaxy is a collection of billions of stars held together by their own gravity
  • Before galaxies are stars formed, the universe was formed of hydrogen and helium 
  • The force of gravity pulled matter into galaxies and stars
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Energy from the nucleus

The life history of a star;

  • A protostar is a gas and dust cloud in space that can go on to form a star
  • Low mass star (sun):
    • Protostar > main sequence star > red giant > white dwarf > black dwarf
  • High mass star:
    • Protostar > main sequence star > red supergiant > supernova > black hole (if sufficient mass)
  • The son will eventually become a black dwarf
  • A supernova is the explosion of a supergiant after its collapses

How the chemical elements formed;

  • Elements as heavy as iron are formed inside stars as a result of nuclear fusion 
  • Elements heavier than iron are formed in supernovas, along with lighter elements
  • The sun and the rest of the solar system were formed from the debris of a supernova
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Force and acceleration;

  • The bigger the resultant force on an object, the greater its acceleration 
  • The greater the mass of an object, the smaller its acceleration for a given force
  • F = m x a

Falling object;

  • The weight of an object = force of gravity on it 
  • The mass of an object = the quantity of matter in it 
  • An object acted on only by gravity accelerates at about 10m/s2
  • The terminal velocity of a falling object = the velocity it reaches when falling through a fluid. The weight is then equal to the drag force on the object
  • The drag force may also be called air resistance or fluid resistance  
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