Physics 2

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How does the acceleration of an object depend on the size of the resultant force?
The bigger the resultant force on an object is, the greater its acceleration is
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What effect does the mass of the object have on its acceleration?
The greater the mad of an object is, the smaller its acceleration is for a given force
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How do we calculate the resultant force on an object from its acceleration and its mass?
Resultant force (newtons, N) = mass (kilograms) x acceleration (meters/second squared)
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What forces oppose the driving force of a car?
Friction and air resistance oppose the driving force of a car
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What does the stopping distance of a vehicle depend on?
The stopping distance of a car depends on the thinking distance and the braking distance
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What factors can increase the stopping distance of a vehicle?
High speed, poor weather conditions and poor maintenance all increase the breaking distance. Poor reaction time and high speed both increase the thinking distance
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What is the difference between mass and weight?
The weight of an object is the force of gravity on it. Its mass is the quantity of matter in it
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What can we say about the motion of a falling object acted on by only gravity?
An object acted on only by gravity accelerates at about 10 m/s squared
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What is terminal velocity?
The terminal velocity of a falling object is the velocity it reaches when it is falling in a fluid. The weight is then equal to the drag force on the object
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How do we measure the extension of an object when it is stretched?
The extension is the difference between the length of the spring and its original length
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How does the extension of a spring vary with the force applied to it?
The extension of a spring is directly proportional to the force applied to it, provided the limit of proportionality is not exceeded
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What is the spring constant of a spring?
The spring constant of a spring is the force per unit extension needed to stretch it
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How can the fuel economy of road vehicles be improved?
Fuel economy of road vehicles can be improved by reducing the speed or fitting a wind deflector
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What is an average speed camera?
Average speed cameras are linked in pairs and they measure the average speed of a vehicle.
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What do we mean by 'work' in science?
Work is done on an object when a force makes the object move
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What is the relationship between work and energy?
Energy transferred = work done
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How do we calculate the work done by force?
Work done (joules) = force (newtons) x distance moved in the direction of the force (metres)
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What happens to the work done to over come friction?
Work done to overcome friction is transferred as energy that heats the objects that rub together and the surroundings
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What does the gravitational potential energy of an object depend on?
The gravitational potential energy of an object depends on its weight and how far it moves vertically
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What happens to the gravitational potential energy of an object when it moves up or down?
The gravitational potential energy of an object goes up and decreases when the object goes down
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How can we calculate the change of gravitational potential energy of an object when it moves up or down?
The change of gravitational potential energy of an object is equal to its mass x the gravitational field strength x its change of height
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What does the kinetic energy of an object depend on?
The kinetic energy of a moving object depends on its mass and its speed
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How can we calculate kinetic energy?
Kinetic energy (J) = 1/2 x mass (kg) x speed squared (m/s squared)
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What is elastic potential energy?
Elastic potential energy is the energy stored in an elastic object when work is done on the object
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How can we calculate momentum?
Momentum = mass x velocity
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What is the unit of momentum?
The unit of momentum is kg m/s
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What happens to the total momentum of two objects when they collide?
Momentum is conserved whenever objects interact, provided the objects are in a closed system so that no external forces act on them
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Why does momentum have direction as well as size?
Momentum is mass x velocity and velocity is speed in a certain direction
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When two objects push each other apart do they move away at different speeds?
When two objects push each other apart, they move apart with different speeds if they have unequal masses
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When two objects push each other apart why is their total momentum zero?
When two objects push each other apart, they move apart with equal and opposite momentum so their total momentum is zero
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When vehicles collide, what does the force of the impact depend on?
When vehicles collide, the force of the impact depends on mass, change of velocity, and the duration of the impact
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How does the impact force depend on the impact time?
The longer the impact time is, the more the impact force is reduced
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What can we say about the impact forces and the total momentum when two vehicles collide?
When two vehicles collide, they exert equal and opposite forces on each other, their total momentum is uncharged
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Why do seat belts and air bags reduce the force on people in care accidents?
Seat belts and air bags spread the force across the chest and they also increase the impact time
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How do side impact bars and crumple zones work?
Side impact bars and crumple zones 'give away' in an impact so increasing the impact time
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How can we work out if a car in a crash was 'speeding'?
We can use the conservation of momentum to find the speed of a car before an impact
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What happens when insulating materials are rubbed together?
Certain insulating materials become charged when rubbed together
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What is transferred when objects become charged?
Electrons are transferred when objects become charged:insulating materials that become positively charged when rubbed lose electrons, insulating materials that become negatively charged when rubbed gain electrons
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What happens when charges are brought together?
Like charges repel; unlike charges attract
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Why are electric circuits represented by circuit diagrams?
Every component has its own agreed symbol. A circuit diagram shows how components are connects together
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What is the difference between a battery and a cell?
A battery consists of two or more cells connected together
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What determines the size of an electric current?
The size of an electric current is the rate of flow of charge
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How can we calculate the size of an electric current from the charge flow and the time taken?
Electric = charge flow/time taken
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What do we mean by potential difference?
The potential different across a component (volts) = work done or energy transferred (in joules) / charge (in coulombs)
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What is resistance and what is its unit?
Resistance (in ohms) = potential difference (volts) / current (amperes)
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What is Ohm's Law?
Ohm's law states that the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor
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What happens if you reverse the current in a resistor?
Reversing the current through a component reverses the pd across it
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What happens to the resistance of a filament bulb as its temperature increases?
Filament bulb : resistance increases with increase of the filament temperature
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What happens with a diode?
'forward' resistance is low, 'reverse' resistance is high
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What happens with a thermistor?
Resistance decreases if its temperature increases
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What happens with a LDR?
Resistance decreases if the light intensity on it increases
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What can we say about the current and potential difference for components in a series circuit?
For components in series: the current is the same in each component, adding the potential difference gives the total potential difference
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How can we find the total resistance of resistors in series?
Adding the resistance of resistors in series
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What can we say about the potential difference of several cells in series?
For cells in series, acting in the same direction, the total potential difference is the sum of their individual potential differences
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What can we say about the currents in the components in a parallel circuit?
For components in parallel: the total current is the sum of the currents through the separate components, the bigger the resistance of a component, the smaller its current is
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What can we say about the potential differences across the components in a parallel circuit?
In a parallel circuit the potential difference is the same across each component
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How can we calculate current through a resistor in a parallel circuit?
To calculate the current through a resistor in a parallel circuit, use this equation : current (amperes) = potential difference (volts) / resistance (ohms)
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What is meant by direct current and alternating current?
Direct current is in one direction only. Alternating current repeatedly reverses its direction
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What do we mean by the peak voltage of an alternating potential difference?
The peak voltage of an alternating potential difference is the maximum voltage measured from zero volts
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What do we mean by the live wire and the neutral wire of a mains circuit?
A mains circuit has a live wire that is alternately positive and negative every cycle and a neutral wire at zero volts
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How do we use an oscilloscope to measure the frequency of an alternating current?
To measure the frequency of an a.c. supply, we measure the time period of the waves then use the formula: frequency = 1 / time taken for 1 cycle
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What is the casing of a mains plug or socket made from and why?
Sockets and plug cases are made of stiff plastic materials that enclose the electrical connections. Plastic is used because it is a good electrical insulator
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What is in a mains cable?
Mains cable consists of two or three insulated copper wires surrounded by an outer layer of flexible plastic material
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What colour are the live, neutral and earth wires?
In a three-pin plug or a three-core cable, the live wire is brown, the neutral wire is blue, and the earth wire is green and yellow
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Why does a 3-pin plug include an earth pin?
The earth wire is connected to the longest pin and is used to earth the metal case of a mains appliance
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What do we use a fuse for?
A fuse contains a thin wire that heats up, melts, and cuts off the current if the current is too large
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Why is a fuse always on the 'live' side of an appliance?
A fuse is always fitted in series with the live wire. This cuts the appliance off from the live wire if the fuse blows
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What is a circuit breaker?
A circuit breaker is an electromagnetic switch that opens and cuts off the current if too much current passes through the circuit breaker
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Why are appliances with plastic cases not earthed?
A mains appliance with a plastic case does not need to be earthed because plastic is an insulator and cannot become live
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What is the relationship between power and energy?
The power supplied to a device is the energy transferred to it each second
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How can we calculate electrical power and what is its unit?
Electrical power supplied (watts) = current (amperes) x potential difference (volts)
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How can we calculate the correct current for a fuse?
Correct rating (in amperes) for a fuse: = electrical power (watts) / potential difference (volts)
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What is an electric current?
An electric current is the rate of flow of charge
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How do we calculate the flow of electric charge from the current?
Charge (coulombs) = current (amperes) x time (seconds)
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What energy transfers take place when charge flows through a resistor?
When an electrical charge flows through a resistor, energy transferred to the resistor makes it hot
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How is the energy transferred by a flow of charge related to potential difference?
Energy transferred (joules) = potential difference (volts) x charge flow (coulombs)
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What can we say about the electrical energy supplied by the battery in a circuit and the electrical energy transferred to the components?
When charge flows round a circuit for a certain time, the electrical energy supplied by the battery is equal to the electrical energy transferred to all the components in the circuit
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Why are electrical faults dangerous?
Electrical faults are dangerous because they can cause electrical shocks and fires
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How can we prevent electrical faults?
Never touch a mains plug or appliance with wet hands, check cables, plugs and sockets for damage regularly, check smoke alarms and infrared sensors regularly
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When choosing and electrical appliance, what factors in addition to the cost should we consider?
When choosing an electrical appliance, the power and efficiency rating of the appliance need to be considered
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How do different forms of lighting compare in terms of cost and energy efficiency?
Filament bulbs and halogen bulbs are much less efficient than low energy bulbs
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What is a radioactive substance?
A radio active substance contains unstable nuclei that become stable by emitting raditation
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What types of radiation are given out from a radioactive substance?
There are three main types of radiation substances- alpha, beta and gamma radiation
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When does a radioactive source give out radiation (radioactive decay)?
Radio active decay is a random event- we cannot predict or influence when it will happen
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Where does back ground radiation come from?
Background radiation is from radioactive substances in the environment or from space or from devices such as x-ray machines
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How was the nuclear model of the atom established?
Rutherford used the measurements from alpha-scattering experiments to prove that an atom has a small positively charged central nucleus where most of the mass of the atom is located
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Why was the plum pudding model of the atom rejected?
The plum pudding model could not explain why some alpha particles were scattered through large angles
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Why was the nuclear model accepted?
The nuclear model of the atom correctly explained why the alpha particles are scattered and why some are scattered through large angles
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What is an isotope?
Isotopes of an element are atoms with the same number of protons bu a different number of neutrons. Therefore they have the same atomic number but a different mass number
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How far can each type of radiation travel in air and what stops it?
Alpha radiation is stopped by paper, and has a range of a few cm in air. Beta radiation is stopped by thin metal and has a range of about a meter in air. Gamma radiation is stopped by thick lead and has an unlimited range in air.
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What is alpha beta and gamma radiation?
Alpha radiation consists of particles, each composed of two protons and two neutrons. Beta radiation consists of fast moving electrons emitted from the nucleus. Gamma radiation consists of electromagnetic radiation
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How can we separate a beam of alpha, beta and gamma radiation?
A magnetic or an electric field can be used to separate a beam of alpha, beta and gamma radiation
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Why is alpha, beta and gamma radiation dangerous?
Alpha, beta and gamma radiation ionise substances they pass through. Ionisation in a living cell can damage or kill the cell
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What do we mean by the 'half-life' of a radioactive source?
The 'half-life' of a radioactive isotope is the average is the average time it takes for the number of nuclei of the isotope in a sample to halve
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What do we mean by the activity of a radioactive source?
The activity of a radioactive source is the number of nuclei that decay per second
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What happens to the activity of a radioactive isotope as it decays?
The number of atoms of a radioactive isotope and the activity both decrease by half every half life
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How do we choose a radioactive isotope for a particular job?
The use we can make of a radioactive isotope depends on a. its half-life b. the type of radiation it gives out
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How can we use radioactivity for monitoring?
For monitoring, the isotope should have a long half-life
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What are radioactive tracers?
Radioactive tracers should be beta or gamma emitters that last long enough to monitor but not too long
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What is radioactive dating?
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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What is nuclear fission?
Nuclear fission is the splitting of a nuclear into two approximately equal fragments and the release of two or three neutrons
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Which radioactive isotopes undergo fission?
Nuclear fission occurs when a neutron hits a uranium - 235 nucleus or a plutonium-239 nucleus and the nucleus splits
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What is a chain reaction?
A chain reaction occurs in a nuclear reactor when each fission event causes further fission events
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How is a chain reaction in a nuclear reactor controlled?
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
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What is nuclear fission?
Nuclear fission is the process of forcing two nuclei close enough together so they form a singer larger nucleus.
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How can nuclei be made to fuse together?
Nuclear fusion can be brought about by making two light nuclei collide at very high speed
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Where does the suns energy come from?
Energy is released when two light nuclei are fused together. Nuclear fusion in the sun's core releases energy
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Why is it difficult to make a nuclear fusion reactor?
A fusion reactor needs to be at a vey high temperature before nuclear fusion can take place. the nuclei to be fused are difficult to contain
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What is random gas and why is it dangerous?
Radon gas is a alpha-emitting isotope that seeps into houses in certain areas through the ground
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How safe are nuclear reactors?
There are thousands of fission reactors safely in use in the world. None of the are of the same type as the chernobyl rectors that exploded
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What happens to nuclear waster?
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 them
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What is a galaxy?
A galaxy is a collection of billions of stars held together by their own gravity.
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What was the universe like in the billions of years before stars and galaxies were formed?
Before galaxies and stars where formed, the universe was a dark patchy cloud of hydrogen and helium
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What is the force responsible for the formation of stars and galaxies?
The force of gravity pulled matter into galaxies and stars
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What is a protostar?
A protostar is a gas and dust cloud in space that can go on to form a star
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What are the stages in the life of a star?
Low mass star: protostar > main sequence star > red giant > white dwarf > black dwarf. High mass star: Protostar > main sequence star > red supergiant > supernova > neutron star > black hole if sufficient mass
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What will eventually happen to the sun?
The sun with eventually become a black dwarf
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What is a supernova?
A supernova is the explosion of a supergiant after is collapses
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What chemical elements are formed inside stars?
Elements as heavy as iron are formed inside stars as a result of nuclear fusion
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What chemical elements are formed in supernovas?
Elements heavier than iron are former in supernovas as well as light elements
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Why does the earth contain heavy elements?
The sun and the rest of the solar system were formed from the debris of a super nova, so the heavy elements prove this fact
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How do we calculate the resultant force on an object from its acceleration and its mass?

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Preview of the front of card 3

Card 4

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What forces oppose the driving force of a car?

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Card 5

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What does the stopping distance of a vehicle depend on?

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