P2 Flashcards
What reactions take place in stars?
During most of a star’s lifetime, hydrogen nuclei fuse together to form helium nuclei. As the star runs out of hydrogen, other fusion reactions take place forming the nuclei of other elements. Heavier elements than hydrogen and helium (up to iron) are formed. Elements heavier than iron are formed in supernovas.
What is a star like during its ‘main sequence’ period of its life cycle?
During its ‘main sequence’ period of its life cycle, a star is stable because the forces in it are balanced. The outward pressure from the expanding hot gases is balanced by the force of the star’s gravity. Our Sun is at this stable phase in its life.
Why does fusion work in stars?
The temperatures and pressures inside a star are so great that nuclear fusion can happen. Stars have enough hydrogen to maintain their energy output for millions of years.
What is the life cycle for stars about the same size as our sun?
Protostar- main sequence star-red giant → white dwarf → black dwarf
What do the elements formed in stars and found in other planets suggest?
Heavy elements are found in the Sun and planets of the solar system. This suggests that the solar system was formed from the remains of earlier stars that exploded as supernovas.
What is the life cycle for stars bigger than our sun?
protostar-Main sequence star → red super giant → supernova → neutron star or black hole
How is a star formed?
Stars form from massive clouds of dust and gas in space. Gravity pulls the dust and gas together. As the gas falls together, it gets hot. A star forms when it is hot enough for nuclear reactions to start. This releases energy, and keeps the star hot.
What are the hazards of radiation?
When radiation collides with molecules in living cells it can damage them. If the DNA in the nucleus of a cell is damaged, the cell may become cancerous. The cell then goes out of control, divides rapidly and causes serious health problems.
The greater the dose of radiation a cell gets, the greater the chance that the cell will become cancerous.
What did they do during the Rutherford’s scattering experiment?
A beam of alpha particles was aimed at very thin gold foil and their passage through the foil detected. The scientists expected the alpha particles to pass straight through the foil, but something else also happened.
What happened as a result of the Rutherford’s scattering experiment?
As a result of this experiment, the plum pudding model was replaced by the nuclear model of the atom.
How does hydrogen fuse to form helium?
A hyrdogen-1 nucleus is made of 1 proton. This can combine with a hydrogen-2 nucleus (which has one proton and one neutron) to form a new nucleus with two protons and one neutron. This is the nucleus of helium-3. So helium-3 has been formed by fusing the hyrodgen-1
How penetrating is Alpha radiation?
Alpha radiation is the least penetrating. It can be stopped - or absorbed - by just a sheet of paper.
What are isotopes?
Isotopes are the atoms of an element with different numbers of neutrons. They have the same proton number, but different mass numbers.
What happens during nuclear fission?
For fission to happen, the uranium-235 or plutonium-239 nucleus must first absorb a neutron. When this happens:
The nucleus splits into two smaller nuclei
Two or three neutrons are released
Some energy is released
The additional neutrons released may be absorbed by other uranium or plutonium nuclei, causing them to split. Even more neutrons are then released, which in turn can split more nuclei. This is called a chain reaction. The chain reaction in nuclear reactors is controlled to stop it going too fast.
What are the uses of radiation?
very high doses of radiation can kill the cell completely. We use this property of radiation to kill cancer cells, and also harmful bacteria and other micro-organisms.
How can the Geiger-Muller tube be used to monitor radiation?
Each time it absorbs radiation, it transmits an electrical pulse to a counting machine. This makes a clicking sound or displays the count rate. The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Muller tube is absorbing.
Why is radiation used as a tracer not usually harmful?
It has a short half-life and so decays before it can do much damage
It is not poisonous
How can the nuclear of an atom be represented?
(A over Z) X
A is the atomic mass (number of protons + neutrons)
Z is the atomic number (number of protons)
X is chemical symbol (as shown on the Periodic Table)
What was the plum pudding model of an atom?
An early model (scientific idea) about the structure of the atom was called the plum pudding model. In this model, the atom was imagined to be a sphere of positive charge with negatively charged electrons dotted around inside it - like plums in a pudding.
What are the two common isotopes used for nuclear fission and why?
Uranium or plutonium isotopes are normally used as the fuel in nuclear reactors because their nuclei are relatively large and easy to split.
What are the charges of the three types or radiation and what does this mean?
Alpha particles are positively charged, beta particles are negatively charged and gamma radiation is electrically neutral. This means that alpha radiation and beta radiation can be deflected by electric fields, but gamma radiation is not deflected. alpha radiation and beta radiation can also be deflected by magnetic fields. Just as with electric fields, gamma radiation is not deflected by magnetic fields.
If the radioactive source is outside the body, which is the most dangerous?
Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body
Beta and gamma radiation are the most dangerous sources because they can penetrate the skin and damage the cells inside
What is nuclear is fission?
‘Fission’ is another word for splitting. The process of splitting a nucleus is called nuclear fission.
Why are emitters of beta or gamma radiation used for tracers?
Emitters of beta radiation or gamma radiation are used because these types of radiation readily pass out of the body, and they are less likely to be absorbed by cells than alpha radiation.
How penetrating is gamma radiation?
Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead or many metres of concrete.
What typically uses nuclear fusion?
The Sun and other stars use nuclear fusion to release energy.
Why do we measure half-life?
Because It is not possible to predict when an individual atom might decay. But it is possible to measure how long it takes for half the nuclei of a piece of radioactive material to decay.
What are the artificial sources of background radiation?
human activity has added to background radiation by creating and using artificial sources of radiation. These include radioactive waste from nuclear power stations, radioactive fallout from nuclear weapons testing and medical x-rays.
What is gamma radiation?
Gamma radiation is very short wavelength - high frequency - electromagnetic radiation. This is similar to other types of electromagnetic radiation such as visible light and x-rays, which can travel long distances.
What do natural sources of background radiation include?
Cosmic rays - radiation that reaches the Earth from space
Rocks and soil - some rocks are radioactive and give off radioactive radon gas
Living things - plants absorb radioactive materials from the soil and these pass up the food chain
How is radiation used?
In smoke detectors
For sterilising medical instruments
For killing cancer cells
For dating rocks and materials such as archaeological finds
In chemical tracers to help with medical diagnosis
For measuring the thickness of materials in, for example, a paper factory
What happens during beta decay?
n beta decay, a neutron changes into a proton plus an electron. The proton stays in the nucleus. The electron leaves the atom with high energy as a beta particle.
The nucleus has one more proton and one less neutron when it emits a beta particle. This means that:
The atomic mass number stays the same
The atomic number increases by 1
What is nuclear fusion?
Nuclear fusion involves two atomic nuclei joining to make a large nucleus. Energy is released when this happens.
What happens during alpha decay?
Two protons and two neutrons are lost from a nucleus when it emits an alpha particle. This means that:
The atomic mass number decreases by 4 The atomic number decreases by 2
A new element is formed that is two places lower in the Periodic Table than the original element.
Who conducted the experiment to disprove the plum pudding model?
A scientist called Ernest Rutherford designed an experiment to test the plum pudding model. It was carried out by his assistants Hans Geiger and Ernest Marsden.
How does the thickness of a substance affect radiation absorbed?
The thicker the substance, the more the radiation is absorbed.
How are tracers used inside the body?
Doctors may use radioactive chemicals called tracers for medical imaging. Certain chemicals concentrate in different damaged or diseased parts of the body, and the radiation concentrates with it. Radiation detectors placed outside the body detect the radiation emitted and, with the aid of computers, build up an image of the inside of the body.
How does hydrogen fuse to form helium?
The sequence of nuclear fusion reactions in a star is complex, but overall hydrogen nuclei join to form helium nuclei. Here is one nuclear fusion reaction that takes place:
Hydrogen-1 nuclei fuse with hydrogen-2 nuclei to make helium-3 nuclei
and hydrogen-2 nuclei.
How do film badges work?
There is a light-proof packet of photographic film inside the badge. The more radiation this absorbs, the darker it becomes when it is developed. To get an accurate measure of the dose received, the badge contains different materials that the radiation must penetrate to reach the film. These may include aluminium, copper, lead-tin alloy and plastic. There is also an open area at the centre of the badge.
What is beta radiation?
Beta radiation consists of high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed.
What does half-life mean?
There are two definitions of half-life, but they mean essentially the same thing:
The time it takes for the number of nuclei of the isotope in a sample to halve The time it takes for the count rate from a sample containing the isotope to fall to half its starting level
What happens to radiation as it gets further away from the radioactive material?
All types of radiation become less intense the further the distance from the radioactive material, as the particles or rays become more spread out.
How can we detect radiation with photographic film?
Photographic film goes darker when it absorbs radiation, just like it does when it absorbs visible light. The more radiation the film absorbs, the darker it is when it is developed. People who work with radiation wear film badges, which are checked regularly to monitor the levels of radiation absorbed.
How is radiation used to monitor the thickness of a material?
Radiation is used in industry in detectors that monitor and control the thickness of materials such as paper, plastic and aluminium. The thicker the material, the more radiation is absorbed and the less radiation reaches the detector. It then sends signals to the equipment that adjusts the thickness of the material.
How do you find the half-life of a radioactive substance from a graph?
It is possible to find out the half-life of a radioactive substance from a graph of the count rate against time. At the point where the counts drop to half of what they original were, is how long the half-life is.
What is alpha radiation?
Alpha radiation consists of alpha particles. An alpha particle is identical to the nucleus of a helium atom, which comprises two protons and two neutrons.
How penetrating is Beta radiation?
Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.
What actually happened during the Rutherford’s scattering experiment?
Some of the alpha particles emerged from the foil at different angles, and some even came straight back. The scientists realised that the positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the atom.
What is radioactive decay?
The nuclei of radioactive atoms are unstable. They break down and change into a completely different type of atom. This is called radioactive decay.
If the radioactive source is inside the body, which is the most dangerous?
Alpha radiation is the most dangerous because it is easily absorbed by cells
Beta and gamma radiation are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it
How do you find the period of an AC supply?
You can find this by looking at the time between one peak and the next, between one trough and the next, or between any two identical places on adjacent oscillations.
What does an ammeter look like?
A circle with an A in it.
What does a variable resister look like?
A resister, but with a sloped arrow through it.
Why do some appliances like hairdryers and vacuums not have an earth wire?
This is because they have plastic casings, or they have been designed so that the live wire cannot touch the casing. As a result, the casing cannot give an electric shock, even if the wires inside become loose. These appliances have double insulation and carry a symbol.
What does a cell and battery look like?
A cell is one long, thin line with a gap between it and another short, thicker line. A battery is multiple cells.
What does it mean if something is a series circuit and what does this mean for the current?
Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows across each component connected in series is the same.
What does a fuse look like?
A rectangle with a horizontal line through it.
What happens when you rub two different insulating materials against each other?
When the materials are rubbed against each other:
Negatively charged particles called electrons move from one material to the other
The material that loses electrons becomes positively charged
The material that gains electrons becomes negatively charged
Both materials gain an equal amount of charge, but the charges are opposite
What do fuses do?
Fuses protect electrical circuits and appliances.
The fuse breaks the circuit if a fault in an appliance causes too much current flow. This protects the wiring and the appliance if something goes wrong.
What does a light emitting diode look like?
It looks like a horizontal triangle, with its tip resting against a straight vertical line. You can see the wire line in the triangle. It is surrounded by a circle, with two arrows pointing away from it at the right side.
What does it mean if something is a parallel circuit and what does this mean for the current?
Components that are connected on separate loops are connected in parallel. The current is shared between each component connected in parallel.
What happens to current if more cells are added?
When more cells are connected in series in a circuit, they produce a bigger potential difference across its components. More current flows through the components as a result.
What does a voltmeter look like?
A circle with a V in it.
What are wires made out of and why?
A mains electricity cable contains two or three inner wires. Each has a core of copper, because copper is a good conductor of electricity. The outer layers are flexible plastic, because plastic is a good electrical insulator.
How do fuses work?
The fuse contains a piece of wire which melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.
What happens to current if two or more components are added?
When two or more components are connected in series, the same current flows through each component.
What does a lamp look like?
A circle with a cross in it.
What does it mean if there is a short circuit?
you can find a way past the lamp without going through any other component.
How do you calculate current?
I = Q ÷ t
I is the current in amperes (amps), A Q is the charge in coulombs, C t is the time in seconds, s
How do you calculate the energy transferred?
E = V×Q
E is the energy transferred in joules, J V is the potential differences in volts, V Q is the charge in coulombs, C
What is power?
Power is a measure of how quickly energy is transferred. The unit of power is the watt, W.
What does a thermistor look like?
A resister with a straight, diagonal line through it which has a horizontal bottom.
What do circuit breakers do?
Circuit breakers also protect electrical circuits and appliances. Residual current circuit breakers, RCCBs, protect some circuits. They detect a difference in the current between the live and neutral wires. RCCBs work much faster than fuses do.
What is the period of an AC supply?
The period of an AC supply is the time taken for one complete oscillation.
How do you measure current?
Current is measured in amperes (which is often abbreviated to amps or A). The current flowing through a component in a circuit is measured using an ammeter. This must be connected in series with the component.
Which colour represents which wire?
Blue= Neutral
Brown=Live
Green with yellow stripes=Earth
What is direct current?
If the current flows in only one direction it is called direct current (DC). Batteries and cells supply DC electricity, with a typical battery supplying around 1.5 V.
Where do the wires go inside the plug?
The blue neutral wire goes to the left, the brown live wire to the right and the green and yellow striped earth wire is on top. The fuse fits next to the live wire.
How do you calculate potential difference?
V = W ÷ Q
V is the potential difference in volts, V W is the work done (energy transferred) in joules, J Q is the charge in coulombs, C
What does a diode look like?
It looks like a horizontal triangle, with its tip resting against a straight vertical line. You can see the wire line in the triangle. It is surrounded by a circle
What is potential difference?
The potential difference between two points in an electric circuit is the work done when a coulomb of charge passes between the points. A potential difference, also called voltage, across an electrical component is needed to make a current flow through it. Cells or batteries often provide the potential difference needed.
What are the features of a plug?
The case is made from tough plastic or rubber, because these materials are good electrical insulators.
The three pins are made from brass, which is a good conductor of electricity.
There is a fuse between the live terminal and the live pin.
The fuse breaks the circuit if too much current flows.
The cable is secured in the plug by a cable grip. This should grip the cable itself, and not the individual wires inside it.
What does a resister look like?
A clear rectangle- You can not see the wire inside the rectangle, it is completely white.
What is current?
Electric current is a flow of electric charge.
What happens to potential difference if two or more components are added?
When two or more components are connected in series, the total potential difference of the supply is shared between them. This means that if you add together the voltages across each component connected in series, the total equals the voltage of the power supply.
What is alternating current?
If the current constantly changes direction, it is called alternating current (AC). Mains electricity is an AC supply, with the UK mains supply being about 230 V.
What is the frequency of an AC supply?
The frequency of an AC supply is the number of oscillations per second.
How do you measure potential difference?
A potential difference, also called voltage, across an electrical component is needed to make a current flow through it. Cells or batteries often provide the potential difference needed.
What does the earth wire work?
The earth wire creates a safe route for the current to flow through if the live wire touches the casing. the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock. A strong current surges through the earth wire because it has a very low resistance. This breaks the fuse and disconnects the appliance.
What does a light dependent resistor look like?
Like a clear rectangle inside a circle, with two arrows pointed towards it at the left side.
How do you calculate power?
P = E ÷ t
P is the power in watts, W E is the energy transferred (or work done) in joules, J T is the time in seconds, s
What happens to the potential difference if more cells are added?
hen two or more cells are connected in series in a circuit, the total potential difference is the sum of their potential differences. For example, if two 1.5 V cells are connected in series in the same direction, the total potential difference is 3.0 V. If two 1.5V cells are connected in series, but in opposite directions, the total potential difference is 0V, so no current will flow.
How else can you calculate power using current and potential difference?
P = I × V
P is the power in watts, W I is the current in amperes (amps), A V is the potential differences in volts, V
How do you find the frequency of an AC supply?
You can find it from the period:
Frequency = 1 ÷ period
Remember to convert to seconds if needed.
What two things are necessary for a circuit to work?
There must be a complete circuit
There must be no short circuits
How do you detect charges?
Two charged objects will repel each other if they have the same type of charge (they areboth positive or both negative). Two charged objects will attract each other if they have opposite charges. The only way to tell if an object is charged is to see if it repels another charged object. This is because charged objects will also attract small uncharged objects.
What is power?
Power is a measure of how quickly work is being done and so how quickly energy is being transferred.
How do you calculate momentum?
p = m × v
p is the momentum in kilograms metres per second, kg m/s m is the mass in kilograms, kg v is the velocity in m/s
How do you calculate the change in gravitational potential energy?
Ep = m × g × h
Ep is the change in gravitational potential energy in joules, J m is the mass in kilograms, kg g is the gravitational field strength in newtons per kilogram, N/kg h is the change in height in metres, m
When does the momentum of an object change?
The object speeds up or slows down
The object changes direction
What does the pendulum do?
The pendulum is a simple machine for transferring gravitational potential energy to kinetic energy, and back again.
Why does the bob’s swing in the pendulum become lower with each swing?
the bob’s swing will become lower with each swing, because some energy is also transferred as heat to the surroundings.
How does the pendulum work?
When the bob is at the highest point of its swing, it has no kinetic energy, but its gravitational potential energy is at a maximum. As the bob swings downwards, gravitational potential energy is transferred to kinetic energy, and the bob accelerates.
At the bottom of its swing, the bob’s kinetic energy is at a maximum and its gravitational potential energy is at a minimum.
As the bob swings upwards, its kinetic energy is transferred to gravitational potential energy again. At the top of its swing, it once again has no kinetic energy, but its gravitational potential energy is at a maximum.
How do you calculate power?
P = E ÷ t
P is the power in watts, W E is the work done (or energy transferred) in joules, J t is the time taken in seconds, s.
What does the conservation of momentum mean?
As long as no external forces are acting on the objects involved, the total momentum stays the same in explosions and collisions. We say that momentum is conserved.
What is gravitational potential energy?
When we are above the Earth’s surface we have potential (stored) energy. This is called gravitational potential energy.If an object is lifted, work is done against gravitational force. The object gains energy.
What is momentum?
A moving object has momentum. This is the tendency of the object to keep moving in the same direction. he momentum of an object also depends on the direction of travel.
How do you calculate the work done?
W = F × d
W is the work done in joules, J F is the force applied in newtons, N d is the distance moved in the direction of the force in metres, m
What does it mean if work is done?
Work is done whenever a force moves something. Whenever work is done, energy is transferred from one place to another. Both energy and work are measured in joules, J.
How would you work out the velocity of an object after a collision?
Step 1 – work out the total momentum before the event (before the collision):
p = m × v
Step 2 – work out the total momentum after the event (after the collision):
Because momentum is conserved, total momentum afterwards is the same.
Step 3 – work out the total mass after the event (after the collision): add the masses of objects together
Step 4 – work out new velocity: v = p ÷ m
How do you calculate kinetic energy?
Ek = ½ × m × v2
Ek is the kinetic energy in joules, J m is the mass in kilograms, kg v is the speed in metres per second, m/s.
What are the two things that affect falling objects?
The weight of the object. This is a force acting downwards, caused by the object’s mass the Earth’s gravitational field
Air resistance. This is a frictional force acting in the opposite direction to the movement of the object.
How do you work out the acceleration?
a = (v – u) ÷ t
a is the acceleration of the object in metres per second squared, m/s2 v is the final velocity in metres per second, m/s u is the initial (starting) velocity in metres per second, m/s t is the time taken in seconds, s
What does velocity mean?
The velocity of an object is its speed in a particular direction.
What would happen if a feather and a hammer were dropped together on the moon?
An astronaut on the Moon carried out a famous experiment. He dropped a hammer and a feather at the same time and found that they landed together. The Moon’s gravity is too weak for it to hold onto an atmosphere, so there is no air resistance. When the hammer and feather were dropped, they fell together with the same acceleration.
How do you calculate the force applied to an elastic object?
F = k × e
F is the force in newtons, N k is the 'spring constant' in newtons per metre, N/m e is the extension in metres, m
This equation works as long as the elastic limit (the limit of proportionality) is not exceeded. If a spring is stretched too much, for example, it will not return to its original length when the load is removed.
What is Hooke’s law?
When an elastic object - such as a spring - is stretched, the increased length is called its extension. The extension of an elastic object is directly proportional to the force applied to it:
What does stopping distance depend on?
stopping distance = thinking distance + braking distance
How do you figure out the spring constant?
It is found by carrying out an experiment. For example, the unloaded length of a spring is measured. Different numbers of slotted masses are added to the spring and its new length measured each time. The extension is the new length minus the unloaded length.Assuming the limit of proportionality (elastic limit) is not exceeded, a graph of force against extension produces a straight line that passes through the origin. The gradient of the line is the spring constant, k.
What is terminal velocity?
The maximum speed of an object, reached when the forces moving the object are balanced by its frictional forces.
What do velocity-time graphs show?
When an object is moving with a constant velocity, the line on the graph is horizontal. When an object is moving with a constant acceleration, the line on the graph is straight but sloped. The steeper the line, the greater the acceleration of the object. Notice that a line sloping downwards - with a negative gradient - represents an object with a constant deceleration (slowing down); whilst a line sloping upwards represents a constant acceleration.
What is braking distance?
The braking distance is the distance taken to stop once the brakes are applied.
What happens when the brakes are applied?
When the brakes are applied, work is done by the friction force between the brakes and the wheels. This:
Reduces the kinetic energy of the vehicle (because its speed decreases) Increases the temperature of the brakes
The greater the value of K…?
The greater the value of k, the stiffer the spring.
What does the gradient of a line on a velocity-time graph represent?
The gradient of a line on a velocity-time graph represents the acceleration of the object.
When do elastic objects store elastic potential energy?
Elastic objects can store elastic potential energy if they are stretched. Elastic objects can also store elastic potential energy when they are squashed. For example, this happens when a squash ball is dropped onto a hard surface.
Work is done on an elastic object when its shape changes and it stores elastic potential energy.
What happens when the forces are not balanced?
When all the forces are not balanced, the resultant force is not zero. In this case, an object accelerates in the direction of the resultant force. This means that:
A stationary object begins to move in the direction of the resultant force
A moving object speeds up, slows down or changes direction depending on the direction of the resultant force
What happens when all the forces are balanced?
When all the forces are balanced, the resultant force is zero. In this case:
A stationary object remains stationary A moving object keeps on moving at the same speed and in the same direction
What is acceleration?
The change in velocity X the time taken. It is measured in meters per second squared.
What does the area under a velocity-time graph represent?
The area under a velocity-time graph represents the distance covered. You can divide it into shapes and work out the area and add it together- It is measured in meters.
How do you calculate acceleration?
a = F ÷ m
(It is more often shown as: F = m × a)
F is the resultant force in newtons, N m is the mass of the object in kilograms, kg a is the acceleration of the object in metres per second squared, m/s2
What is the resultant force?
An object may have several different forces acting on it, which can have different strengths and directions. But they can be added together to give the resultant force. This is a single force that
What is the difference between weight and mass?
Weight is not the same as mass. Mass is a measure of how much stuff is in an object. Weight is a force acting on that stuff. Weight is the result of gravity. The Earth’s gravity attracts objects towards the centre of the Earth and you feel forces like this as weight.
What are the three stages of falling?
At the start, the object accelerates downwards because of its weight. There is no air resistance. There is a resultant force acting downwards.
As it gains speed, the object’s weight stays the same, but the air resistance on it increases. There is a resultant force acting downwards.
Eventually, the object’s weight is balanced by the air resistance. There is no resultant force and the object reaches a steady speed, called the terminal velocity.
What does the gradient in a distance-time graph represent?
The gradient of a line on a distance-time graph represents the speed of the object.
How do you work out the gradient in a distance-time graph?
To calculate the gradient of the line on a graph, divide the change in the vertical axis by the change in the horizontal axis.
How do you calculate somethings weight?
W = m × g
W is the weight in newtons, N m is the mass in kilograms, kg g is the gravitational field strength in newtons per kilogram, N/kg.
What factors increase the thinking distance?
The thinking distance increases if the reaction time increases. This can happen if the driver is:
Tired Distracted Under the influence of alcohol or other drugs
The thinking distance also increases as the car’s speed increases (as the car will travel further during the reaction time).
What factors increase the braking distance?
The car’s brakes or tyres are in poor condition
The road and weather conditions are poor (icy or wet roads, for example)
The braking distance also increases as the car’s speed increases.
What do distance-time graphs show?
When an object is stationary, the line on the graph is horizontal. When an object is moving at a steady speed in a straight line, the line on the graph is straight but sloped. Note that the steeper the line, the greater the speed of the object.
How can you calculate the speed of an object?
When an object moves in a straight line at a steady speed, you can calculate its speed:
speed = distance travelled ÷ time taken
Speed is measured in metres per second, m/s Distance is measured in metres, m Time taken is measured in seconds, s
What are the forces acting on a moving vehicle?
Gravity pulls down on the car
The reaction force from the road pushes up on the wheels
The driving force from the engine pushes the car along
There is friction between the road and the tyres
Air resistance acts on the front of the car
What is thinking distance?
It takes time for a driver to react to a situation and start to apply the brakes. The car carries on moving during this reaction time. The thinking distance is the distance travelled in this reaction time.
