AQA Physics 2

AQA Physics 2

1. Motion

   • 1.1 Distance-time graphs
     • These are used to describe the motion of an object
     • Speed (m/s) = distance (m) / time (s)
     • Keywords: Speed
   • 1.2 Velocity and acceleration
     • The velocity of an object is its speed in a given direction
     • If an object change direction but has the same speed, its velocity still stays the same
     • a = (v - u) / t
     • Keywords: Velocity, Acceleration, Deceleration
   • 1.3 More about velocity-time graphs
     • The gradient of the line on a velocity-time graph represents acceleration
     • The area under the line of a velocity-time graph represents the distance travelled in a given time
   • 1.4 Using graphs
     • The gradient of a graph is an object's speed on a distance-time graph
     • The gradient of a graph is an object's acceleration on a velocity-time graph
     • The area under a velocity-time graph is the distance travelled over that time period
     • Always use the measurements from the graph in calculations

2. Forces

   • 2.1 Forces between objects
     • Forces are measured in newtons (N)
     • Objects always exert equal and opposite forces
     • Keywords: Force, Newton
     • An example of equal and opposite forces is driving along a road
   • 2.2 Resultant Force
     • When resultant force is 0 an object is either at rest or continues moving at the same speed in the same direction
     • Keyword: Resultant force
     • When resultant force is not 0, an object will accelerate from rest, accelerate or deccelerate
   • 2.3 Force and acceleration
     • F = m x a
     • A resultant force always causes acceleration
     • The greater the resultant force, the greater the acceleration
     • Keyword: Mass
   • 2.4 On the road
     • If a vehicle travels at a steady speed along the road, the resultant force is zero
     • The faster the speed of a vehicle, the bigger the deceleration needed
     • Stopping distance is thinking distance + braking distance
       • Both TD and BD can be increased through drugs and alcohol or conditions
     • Keywords: Stopping distance, thinking distance, braking distance
   • 2.5 Falling objects
     • An object accelerates to the earth's surface at 9.81m/s²
     • F = m x a
     • W (N) = m x g
     • If an object is on earth, g is called gravitational field strength
     • If an object falls through a fluid, the fluid exerts a drag force on the object
     • The object can only accelerate to a certain speed, called terminal velocity
     • Keywords: Weight, gravitational field strength, drag force, terminal velocity
   • 2.6 Stretching and squashing
     • F = k x e (Hooke's Law)
     • Keywords: Elasticity, directly proportional, limit of proportionality, Hooke's law
     • Objects and materials that extend when weight is placed on them are called elastic
     • k = the spring constant in newtons per m, N/m. The stiffer a spring, the greater its spring constant
     • When an object is stressed, work is done. This is stored as elastic potential
   • 2.7 Force and speed issues
     • Reducing the speed of a vehicle reduces the amount of fuel it uses per mile
     • Reducing air resistance also improves fuel economy
     • Speed cameras are used to discourage speeding
     • Anti-skid surfaces are used to prevent skidding

3. Work, energy and momentum

   • 3.1 Energy and work
     • When an object moves, a force must have been applied
     • Both work and energy have the unit joule, J
     • W = F x d
     • Work done = energy transferred
     • Work done to overcome friction is mainly transferred into energy by heating
     • Keywords: Work, friction
   • 3.2 Gravitational potential energy
     • GPE is energy stored in an object because of its position in Earth's gravitational potential
     • E = m x 9.81 x h
     • Power is the rate of transfer of energy
     • P = E / t
     • Keywords: Gravitational potential energy, power
   • 3.3 Kinetic energy
     • All moving objects have kinetic energy. The greater the mass, the faster the speed
     • E = 1/2 x m x v²
     • Keywords: Kinetic energy, elastic potential energy
   • 3.4 Momentum
     • All moving objects have momentum. The greater the mass and velocity and the greater the momentum
     • p = m x v
     • Momentum is conserved whenever objects interact, provided no external forces act on them
     • Keywords: Momentum, conservation of momentum
   • 3.5 Explosions
     • p = m x v
     • Like velocity momentum has both size and direction
     • When two objects push each other, they move apart at different speeds if they are unequal weights
   • 3.6 Impact forces
     • When vehicles collide, the force of the impact depends on mass, change of velocity and the duration of impact
     • When two vehicles collide they exert equal and opposite forces on one another
     • Keywords: Impact time, crumple zone
   • 3.7 Car safety
     • Seat belts and air bag spread the force across the chest and increase the impact time
     • Side impact bars and crumple zones 'give way' in an impact so increasing the impact time
     • We can use the conservation of momentum to find the speed of a car before impact

4. Current electricity

   • 4.1 Electrical charges
     • Certain insulating materials become charged when rubbed together
     • Electrons are transferred when objects become charged
     • Like charges repel, unlike charges atract
     • Keywords: Insulating, electron, attract, repel
   • 4.2 Electric circuits
     • Every component has its own agreed symbol
     • I = Q / t
   • 4.3 Resistance
     • V = W / Q = E / Q
     • R = V / I
     • Ohm's law states that the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor
     • Reversing the current through a component reversing the potential difference across it
     • Keywords: Series, potential difference, parallel, volt (V), resistance, Ohm's law, ohmic conductor
   • 4.4 More current-potential difference graphs
     • In a filament bulb, resistance increases with increase of the filament temperature
     • In a diode the forward resistance is low and the reverse high
     • In a thermistor, resistance increases as temperature decreases
     • In a light-dependent resistor, resistance decreases as light intensity decreases
     • Keywords: Filament bulb, diode, light-dependent resistor, thermistor
   • 4.5 Series circuits
     • In a series circuit, the current is the same in each component
     • Adding the potential differences gives the total potential difference
     • Adding the resistances gives the total resistance
     • I = V / R
   • 4.6 Parallel circuits
     • For components in parallel, the total current
     • 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

5. Mains Electricity

   • 5.1 Alternating current
     • Direct current is in one direction only. Alternating current repeatedly reverses its current
     • The peak voltage of an alternating potential difference is the maximum voltage measured from 0 volts
     • f = 1 / T
     • Keywords: Direct current, alternating current, frequency, live wire, neutral wire, oscilloscope
   • 5.2 Cables and plugs
     • Sockets and plugs are made of stiff plastic materials, which enclose the electrical connecions
     • Cables consist of 2 or 3 insulated copper wires surrounded by an outer layer of flexible plastic material
     • In a 3 pin plug or cable there is a live (brown), neutral (blue) and earth wire (green/yellow)
     • Keywords: Socket, cable, 3-pin plug
   • 5.3 Fuses
     • A fuse contains a thin wire that heats up and melts if too much current passes through it which cuts the current
     • A circuit breaker is an electromagnetic switch that opens and cuts the current off if too much current passes through it
     • Keywords: Fuse, circuit breaker, residual current circuit breaker (RCCB)
   • 5.4 Electrical power and potential difference
     • The power supplied to a device is the energy transferred to it each second
     • P = I x V
     • The correct rating for a fuse is power (watts) / volts
   • 5.5 Electrical energy and charge
     • An electrical current is the rate of flow of charge
     • Q = I x t
     • When charge flows through a resistor, energy transferred to a resistor makes it hot
     • E = V x Q
   • 5.6 Electrical issues
     • Electrical faults are dangerous because they can cause electric shocks and fires
     • Never touch a mains appliance with wet hands. Never touch a bare wire or terminal at a potential difference of more than ≥ 30 v
     • Check cables, plugs and sockets for damage regularly

6. Radioactivity

   • 6.1 Observing nuclear radiation
     • A radioactive substance contains unstable nuclei that become stable by emitting radiation
     • There are 3 main types of radiation from radioactive substances, alpha (α), beta (ß) and gamma (Γ)
     • Radioactive decay is a random event and we cannot influence or predict when it'll happen
     • Background radiation is from radioactive substances in the environment, space or X-rays
     • Keywords: Nucleus, proton, neutron, electron, alpha, beta, gamma (radiation)
   • 6.2 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 nucleus where most of the mass of the atom is located
     • The nuclear model of the atom correctly explained why the alpha particles are scattered and why some are scattered through larger angles
   • 6.3 Nuclear reactions
     • Isotopes of an element are atoms with the same number of protons but different number of neutron. Therefore they have the same atomic numbers but different mass numbers
     • Alpha decay is a loss of 2 protons and neutrons from the nucleus
     • Beta decay is when a neutron in the nucleus changes into a proton and an electron
     • Keywords: Ion, isotope, atomic number, mass number
   • 6.4 More about different radiation types
     • α radiation is stopped by paper or a few cm of air
     • ß radiation is stopped by thin metal or roughly 1m of air
     • Γ radiation is stopped by 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
     • Keyword: Ionisation
   • 6.5 Half-life
     • 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 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
     • Keyword: Half-life
   • 6.6 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
     • Keywords: Tracer, radioactive dating

7. Energy from the nucleus

   • 7.1 Nuclear fission
     • Nuclear fission is the splitting of a nucleus into two approximately equal fragments and the release of 2 or 3 neutrons
     • Nuclear fission occurs when a neutron hits a uranium-235 or plutonium-239 nucleus which splits it
     • A chain reaction occurs when neutrons from 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
     • Keywords: Nuclear fission, chain reaction
   • 7.2 Nuclear fusion
     • Nuclear fusion is the process of forcing two nuclei close enough together so they form a single larger nucleus
     • Keywords: Nuclear fusion
     • Energy is released when two light nuclei are fused together
   • 7.3 Nuclear issues
     • Radon gas is an α-emitting isotope that seeps into houses in certain areas through the ground
     • There are thousands of fission reactors safely in use throughout the world. None of them are of 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 is removed from it
   • 7.4 The early universe
     • A galaxy is a collection of billions of stars held together by their own gravity
     • Before galaxies and stars formed, the universe was formed of hydrogen and helium
     • The force of gravity pulled matter into galaxies and stars
     • Keywords: Gravitational attraction, star
   • 7.5 The life history of a star
     • Keywords: Protostar, main sequence star, red giant, white dwarf, black dwarf, supergiant, supernova, neutron star, black hole
     • A protostar is a gas and dust cloud in space that can go on to form a star
     • Low mass stars follow the path: protostar, MS star, red giant, white then black dwarf
     • High mass stars follow the path: protostar, MS star, red supergiant, supernova, black hole (if sufficient mass)
     • The sun will eventually become a black dwarf
     • A supernova is the explosion of a supergiant after it collapses
   • 7.6 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