Transcript P2 Revision

P2 Revision
Speed and Velocity
SPEED – how fast your going
VELOCITY – how fast you going and the direction
S
VxT
S = Displacement measured in metres (m)
V = Velocity measured in m/s
T = Time measured in seconds (s)
EXAMPLE;
A cat skulks 20 metres in 35 seconds
Find a) average speed b) how long it takes to skulk 75m
a) V = s/t = 20/35 = 0.5714 = 0.57m/s
b) T = s/v = 75/0.5714 = 131s = 2mins 11s
Acceleration
Acceleration is how quickly the velocity is changing
(v-u)
A x T
V = final velocity measured in m/s
U = initial velocity measured in m/s
A = acceleration measured in m/s²
T = Time taken measured in seconds (s)
EXAMPLE;
A skulking cat accelerated from 2m/s to 6m/s in 5.6s. Find its acceleration
ANSWER;
A = (v-u)/t
(6-2)/5.6 = 4/5.6 = 0.71 m/s²
Velocity Time Graphs
• GRADIENT = ACCELERATION
• Flat sections represent a steady speed
• Steeper the graph, the greater the acceleration/deceleration
• Uphill sections (/) are acceleration
• Downhill sections (\) are deceleration
• The area under any section of the graph = distance travelled in that time
• A curve means changing acceleration
CALCULATING;
 Acceleration = gradient = vertical change
horizontal change
 Velocity = read off the value from the velocity axis
 Distance travelled = in any time interval is equal to the area under the graph
Forces
Six different forces;
 Gravity/Weight – always acting straight downwards
 Reaction force from a surface – acting straight upwards
 Thrust/Push/Pull due to an engine speeding up something
 Drag/Air Resistance/Friction – slowing something down
 Lift due to an aeroplane wing
 Tension in a rope or cable
There are five different force diagrams;
1) STATIONARY OBJECT – All forces in balance
Reaction
- Gravity/Weight is acting downwards
- Reaction Force pushing up
- So all forces are balanced
- Without reaction force it would accelerate downwards
due to the pull of gravity
- The 2 horizontal forces must be equal and opposite (or
zero) otherwise the object will accelerate sideways
Weight/Gravity
2) STEADY HORIZONTAL VELOCITY – All forces balanced
Reaction
Thrust
Drag
Weight
3) STEADY VERTICAL VELOCITY – All forces balanced
Drag
Weight
To move with
a steady
speed the
forces must
be in balance.
If there is an
unbalanced
force then you
get
acceleration,
not a steady
speed.
4) HORIZONTAL Acceleration – unbalanced forces
acceleration
5) VERTICLE ACCELERATION – unbalanced forces
acceleration
1) You only get
acceleration with
an overall resultant
(unbalanced) force
2) The bigger this
unbalanced force is
the greater the
acceleration. Note;
that the forces in
the other direction
are still balanced.
So if the
acceleration is
vertical, the
horizontal forces
are still balanced
Friction Forces
FRICTION SLOWS THINGS DOWN;
- If an object has no force it will always slow down and stop because of friction
- Friction always acts in the opposite direction to movement
- To travel at a steady speed, the driving force needs to balance the frictional forces
- You get friction between 2 surfaces in contact or when a object pas through a
fluid (drag)
RESISTANCE/DRAG FROM FUILDS/AIR/LIQUID;
- The most important factor in reducing drag in fluids is keeping the shape of the
object streamlined, like boat hulls. The opposite extreme is a parachute which is
bout high drag.
DRAG INCREASES AS THE SPEED INCREASES;
Resistance from fluids increases with speed. A car has much more friction to work
against when travelling at 70mph compared to 30mph. So t 70mph the engine has
to work much harder to maintain a steady speed. Therefore it uses more petrol.
Terminal Velocity
When the downward force of gravity/weight equals the
upward force of the air resistance and the objects
stops accelerating because the forces are balanced
and travels at a constant speed
The terminal velocity of any object depends on the drag
in comparison to its weight. The drag depends on its
shape and area. So a skydiver covers a small area, he
will reach terminal velocity at around 120mph. Where
as a skydiver with an open parachute will reach
terminal velocity at 15mph – a much safer speed to hit
the ground. This is due to the fact there is more air
resistance .
Forces and Acceleration
If the forces on an object are all BALANCED, then it’ll keep moving at the SAME
SPEED in the SAME DIRECTION. (if it starts off still it will stay still)
- When something is moving at a constant speed without changing direction – all
the forces must be balanced
- You NEVER need a constant overall force to keep them moving
- To keep a steady speed there must be NO RESULTANT FORCE
If there is an UNBALANCED FORCE, then the object will ACCELERATE in the
direction of the force. The size of the acceleration is decided by the formula:
F = ma
- An unbalanced force will always produce acceleration/deceleration
- This acceleration can take 5 different forms: starting, stopping, speeding up,
slowing down and changing direction
- On a force diagram the arrows will be unequal
The overall UNBALANCED FORCE is often called the RESULTANT FORCE
F
MxA
F = Resultant force measured in Newton's (N)
M = Mass measured in kg
A = Acceleration measured in m/s²
 The bigger the force - the greater the acceleration/deceleration
 The bigger the mass - the smaller the acceleration
 To get a big mass to accelerate as fast as a small mass, it needs a bigger
force. Just think about pushing a heavy shopping trolley
EXAMPLE:
What force is needed too accelerate a mass of 12kg at 5m/s²
ANSWER:
F = ma
F = 12 x 5 = 60N
Reaction Forces
If object A EXERTS A FORCE on object B then object B exerts
THE EXACT OPPOSITE FORCE on object A!
• That means if you push against a wall, the wall will push back against
you just as hard. And as soon as you stop pushing, so does the wall. If
you think about it, there must be an opposing force when you lean
against a wall – other you and the wall would fall over
• If you pull a cart, whatever force you exert on the rope, the rope
exerts the exact opposite pull on you.
• If you put a book on a table, the weight of the book acts downwards
on the table and the table exerts an equal and opposite force
upwards on the book
WHENEVER AN OBJECT IS ON A HORIONTAL SURFCE THERE’LL ALWAYS BE A
RACTION FORCE PUSHING UPWARDS, SUPPORTING THE OBJECT. THE TOTAL
REACTION FORCE WILL BE EQUAL AND OPPOSITE TO THE WEIGHT
Stopping Distances
The distance it takes to stop a car is divided into thinking and braking distance
THINKING DISTANCE; It is affected by three main factors;
-
How fast you’re going – whatever your reaction time, the faster you’re going,
the further you’ll go
How dopey you are – affected by tiredness, drugs, alcohol and old age
How bad the visibility is – lashing rain and oncoming lights etc make hazard
harder to spot
BRAKING DISTANCE; It is affected by four main factors;
-
How fast your going – the faster your going, the further it takes to stop
How heavily loaded the vehicle is – with the same brakes, a heavily loaded
vehicle takes longer to stop. A car won’t stop as quick when its full of people
and luggage and lowing a caravan
How good your brakes are – all brakes must be checked and maintained
regularly. Worn/faulty brakes will let you down catastrophically
How good the grip is – this depends on three things, road surface, weather +
tyres
SPEED LIMITS; they are so important because of how long it takes
cars the break.
Leaves and diesel spills and much on the road are serious hazards
because they’re unexpected. Wet/icy roads are always much
more slippy than dry roads, but often you only discover this
when you try to brake hard! Tyres should have a minimum
tread depth of 1.6mm. This is essential for getting rid of the
water in wet conditions. Without tread, a tyre would simply
ride on a layer of water and skid very easily. This is called
aquaplaning.
Momentum
Momentum = Mass x Velocity
Kg m/s
m/s
kg
• The greater the mass and velocity of an object the more momentum
• Momentum is a vector quantity – it has size and direction (like velocity)
Force Acting =
Newton's
Change in Momentum
Time taken for change to happen
Kg m/s
s
• When a force acts on an object, it causes a change in momentum
• A larger force = faster change of momentum (& greater acceleration)
Car Safety
If someone's momentum changes very quickly, like in a car crash the forces on
the body will be very large – and would cause injury. This is why cars are
designed to slow people down over a longer time when they have a crash
– the longer it takes for a change in momentum – the smaller the force.
SAFETY FEATURES;
 CRUMPLE ZONES – crumple on impact, increasing the time taken for the
car to stop.
 SEAT BELTS – stretch slightly increasing the time taken for the wearer to
stop. This reduces the forces acting on the chest. Seat belts reduce the
number of deaths in car crashes by 50%.
 AIR BAGS – they slow you down more slowly and reduce the number of
deaths in car crashes by 30%.
Taking Risks
Reasons why people take risks;
-
The degree of familiarity – cars are not a risk to us as we use them all the time
Whether you are forced to do something or you choose to
Whether you feel in control of the situation – many people think driving a car
is safer than flying because they are in control
- Possible rewards – you do something because you enjoy it
- Personal experiences – if someone you know had a nasty bungee jumping
accident – you probably wouldn’t want to do it yourself
- Age/personality types
You can estimate the risk of something happening based on how many times it’s
happened – its called a “statistical risk assessment. Or you can use a scientific
theory to model the situation, then calculate the probability. Generally risk
assessors use a combination of the two to get the best possible estimate.
Work
When a force moves an object, energy is transferred and work is done
Whenever something moves, something else is providing some sort of ‘effort’ to
move it. This thing needs a supply of energy. It then does ‘work’ by moving the
object – and one way or the other it transfers the energy it receives into other
forms.
W
F x S
W = Work Done measured in Joules (J)
F = Force measured in Newton's (N)
S = Distance measured in metres (m)
Work Done and Energy Transferred are the same thing
EXAMPLE;
Some kids drag an old tractor tyre 5m over rough ground. They pull with a total force
of 340N. Find the energy transferred
ANSWER;
W = F x S = 340 x 5 = 1700J
Kinetic Energy
Anything moving has kinetic energy – its the energy of movement
K.E.
½ x m x v²
KE = Kinetic energy measured in Joules (J)
½ = one half
M = Mass measured in kg
If the Mass is ever written in g convert it to kg – e.g. 140g = 0.14kg
V = Velocity measured in m/s
EXAMPLE;
A car of mass 2450kg is travelling at 38m/s. Calculate it kinetic energy
ANSWER;
KE = ½mv² = ½ x 2450 x 38² = 1768900
Electrical Energy
Anything which supplies electricity is also supplying electrical
energy. They transfer energy to components in the circuit.
E
VxIxT
E = Electrical energy measured in Joules (J)
V = Voltage measured in Volts (V)
I = Current measured in Amps (A)
T = Time measured in Seconds (s)
Even if something is written in minutes transfer it to seconds
EXAMPLE;
The motor in an electric toothbrush is attached to a 3V battery. If a
current of 0.8A flows through the motor for 3 minutes; what is
the energy transformed
ANSWER;
E = V x I x T = 3 x 0.8 x (3 x 60) = 432J
Gravitational Potential Energy
It is the energy due to height. On Earth, gravity is 10m/s²
P.E.
MxGxH
PE = Gravitational Potential Energy measured in Joules (J)
M = Mass measured in kg
G = Gravity, on earth it is 10m/s²
H = Height measured in metres (m)
EXAMPLE;
A sheep of mass 47kg slowly raised through 6.3m. Find the gain in
potential energy
ANSWER;
PE = M x G x H = 47 x 10 x 6.3 = 2961J
Conservation of Energy
ENERGY CONSERVATION; using less fossil fuels because of the damage it does and
they might run out.
PRINCIPLE OF THE CONSERVATION OF ENERGY; Energy can never be created nor
destroyed – only converted from one form to another. Energy is only useful
when it’s converted from one form to another.
Calculating the Speed of Falling Objects;;
Kinetic energy gained = Potential energy lost
EXAMPLE;
A mouldy tomato of mass 140g is dropped from a height of 1.7m. Calculate its
speed as it hits the floor.
ANSWER;
1) Find the PE lost; PE = M x G x H = 0.14 x 10 x 1.7 = 2.38J
2)
3)
4)
NEEDS TO BE COMPLETED PAGE 49
REV GUIDE
Not all energy transferred is useful that's why
electrical are rarely 100% efficient!
EXAMPLES;
- When you boil a kettle some energy is lost as
sound and as heat to the room
- A light bulb looses some energy as heat to the
room
Power
Power = Rate of doing Work
W
P x T
W = Work Done measured in Joules (J)A
P = Power measured in Watts (W)
T = Time measured in seconds (s)
EXAMPLE;
A motor transfers 4.8KJ of useful energy in 2 minutes. Find its
power output
ANSWER;
P = W/T = 4800/120 = 40W
Power Output
E
P x T
E = Energy Transferred measured in Joules (J)
P = Power measured in Watts (W)
T = Time measured in seconds (s)
THE TIMED RUN UPSTAIRES; in this case the energy transferred is the potential
energy you gain. Hence power = mgh t
Power Output – E Transferred/Time = mgh/t
= 62kg x 10 x 12m
= 531W
14s
THE TIMED ACCELERATION; the energy transferred is the kinetic energy you gain.
Hence Power = ½mv² t
Power Output – Energy Transferred/Time = ½mv² t
= ½ x 62kg x 8m/s²
= 496W
Circular Motion
•
•
Velocity is constantly changing
If an object is travelling in a circle it is constantly changing direction, which means it’s
accelerating. This means there must be a force acting on it (F = ma). This force acts
towards the centre of the circle and is called a centripetal force.
CAR GOING ROUND A BEND; the bend is part of a circle, the
centripetal force is towards the centre of the circle. The force is
from friction between the cars tyres and the road.
BUCKET WHIRLING ROUND ON A ROPE; the centripetal force comes
from the tension in the rope. Break the rope and the bucket flies
off at a tangent.
A SATTELITE ORBITING EARTH; the centripetal force keeping the
satellite in a circular orbit is the gravitational force between Earth
and the satellite.
Roller Coasters
Max GPE
Max Accel
Zero G
Min KE
Min Speed
Min Accel
Min GPE
Max KE
Max Speed
Min Accel
Min GPE
To Loop the Loop You Need A Centripetal Force
When you loop the loop you feel heavier at the bottom of the loop
than you do at the top. During the loop two forces are acting on
you;
- Your weight always acts towards the ground
- A reaction force from you seat which always acts towards the
centre of the loop
These two forces combine to a resultant centripetal force. The two
simplest cases are when you’re at the very top and very bottom of
the loop.
TOP – both weight and reaction force are acting in the same direction
BOTTOM – the two forces are acting in opposite directions
Einstein’s Relativity
THOUGHT EXPERIMENTS; theory's based on theoretical ideas and have not been
tested. Examples are Einstein's theory of relativity.
Scientists can be reluctant to accept new theories, especially if they challenge the
established way of thinking. Newton's laws of motion predicted that the speed
of a ray of light, relative to you, should depend on your velocity – just like the
speed of everything else. These laws had stood for over 200 years, so when
Einstein came along and questioned them it was a big deal. A radical theory like
this is much more likely to be accepted if its the work of more tan one person.
Makes sense if you think about it – the theory cant really be dismissed as one
person . Makes sense if you think about it – the theory cant really be dismissed
as one persons crazy ideas. Before Einstein's theory was published, several
other scientist were already working in similar areas. In the 1880’s, two
American physicists, Albert Michelson and Edward Morely carried out
experiments that suggested that the speed of light was always the same. And
Dutch physicist Hendrik Lorentz had already produced work on the effect of
motion on space and time. Observations which support a theory can greatly
increase its chance of acceptance, e.g. Observations made during a solar
eclipse in 1919 supported Einstein's predication that light s bent by gravity
A Good Theory Should Make Predication That Can Be Tested
1. Einstein's theories made very precise predications about the effects of
motion on time
2. These predications couldn’t be tested for many years because our
equipment wasn’t accurate enough
3. However once testing did become possible, his predications worked in
many situations.
EXAMPLES;
ATOMIC CLOCKS; scientists flew atomic clocks in a plane around the world
and measured the time taken. The time measured by the moving clocks
was very slightly different from that measured by the stationary clocks
on the ground. It appeared that time pass more slowly on the moving
plane
COSMIC RAYS; cosmic rays can produce very short-lived particles called
muons. When muons are moving at close to the speed of light, their
lifetime increases, i.e. Time moves more slowly for them
Ionising Radiation
The more ionising the radiation is, the less penetrating it is
ALPHA PARTICLES;




They are Helium Nuclei
They are big, heavy and slow moving
They have a strong positive charge.
Their big mass and charge makes them strongly ionising –
so they bash into lots of atoms and knock electrons off
them, which creates lots of ions, hence the term ionising.
 So they don’t penetrate far into materials – but are
stopped quickly
 They are blocked by paper and skin
BETA PARTICLES;






They are Electrons.
They move quite fast and they are quite small.
They have a negative charge.
They are moderately ionising
Penetrate moderately before colliding.
For every Beta Particle emitted a neutron turns
into a proton in the nucleus.
 They are blocked by thin metals such as
aluminium
GAMMA RAYS;
 Very short wavelength EM Waves.
 They tend to pass through rather than collide with
atoms, so they are weakly ionising
 Penetrate a long way into materials. Eventually they hit
something and do damage.
 They are similar to X – rays the only difference is where
they come from, X – rays comes from firing electrons are
a piece of metal and gamma rays come from unstable
atomic nuclei when they decay
 They are blocked by thick lead or very thick concrete
Background Radiation
Cosmic Rays come mostly from the Sun. Luckily, the Earths atmosphere protects us from
much of this radiation. The Earths magnetic field also deflects cosmic rays away from
Earth. Radiation due to human activity, e.g. Fallout from nuclear explosions or dumped
nuclear waste.
THE LEVEL OF BACKGROUND RADIATION CHANGES DEPENDING ON WHERE YOU ARE; At
high altitudes it increases because of more exposure to cosmic rays. That means pilots
have an increased risk of getting some types of cancer. Underground in mines it
increases because of the rocks all around. Certain underground rocks like granite can
cause higher levels at the surface, especially if they release radioactive radon gas –
which tends to get trapped in peoples houses.
Radon Gas
Cosmic Rays
Rocks and Building
Materails
Nuclear Industry
Medical X-Rays
Food
Radon Gas;
• The radon concentration in peoples houses varies widely across
the UK, depending on what type of rock the house is built on.
• Studies have shown that exposure to high does of radon gas can
cause lung cancer and the greater the radon concentration the
higher the risk.
• The scientific community is a bit divided on the effect of lower
concentration doses and threes still debate of what the safe(ish) is.
• Evidence suggests that the risk of developing lung cancer from
radon is high greater for smokers compared to non smokers
• Some medical professionals reckon that about 1 in 20 deaths from
lung cancer (2000 a year) are caused by radon exposure
• New houses in areas where high levels of radon gas might occur
must be designed with good ventilation systems. These reduce the
concentration of radon in the living space. In existing houses the
Government recommends that ventilation systems are put in
wherever the radon concentration is higher than a certain level
Isotopes & Radiation
PARTICLE MASS
CHARGE
RADIATION
CHARGE
Proton
1
+1
Alpha
+2 (2 Protons)
Neutron
1
0
Beta
-1 (Electron)
Electron
1/2000
-1
Gamma
0 no charge waves
ISOTOPES; Atoms with the same number of protons by different number of
neutrons. Hence they have the same atomic number but different atomic number.
Most elements have different isotopes, but only 1 or 2 are stable. The other
isotopes tend to be radioactive, which means they decay into other elements and
give out radiation.
RADIATION; Unstable nuclei will decay and in the process give out radiation. This
produce is random – this means if you have 1000 unstable nuclei you can’t say when
any one of them is going to decay and neither can you do anything at all to make a
decay happen. It’s will decay when it wants to and isn’t affected by physical conditions
or chemical bonding. When a nucleus does decay it will spit out one or more of the
three types of radiation. You can write these decays as nuclear equations but the mass
and atomic numbers much be equal on both sides;
Half-Life
Half-Life is the time taken for Half of the radioactive atoms now present to decay.
Each time a decay happens and an alpha/beta/gamma particle is given out – so
one more radioactive nucleus has disappeared. As the unstable nuclei all
steadily disappear, the activity as a whole will decreases. So the older a sample
becomes, the less radiation it will emit
WORKING OUT THE HALF-LIFE; use a step by step method and divide by 2 each
time. Example;;
Initial Count
640
after ONE half life
320
after THREE half lives
80
It has got four half lives.
after TWO half lives
160
after FOUR half lives
40
MEASURING THE HALF-LIFE OF A SAMPLE USING A GRAPH;;
The half life is found from the graph, by finding the time interval on the bottom axis
corresponding to a halving of the activity on the vertical axis.
Background Rate; 20/min
Subtract the Background Rate from every reading to give an accurate number
Uses of Ionising Radiation
SMOKE DETECTORS – USE ALPHA RADIATION;
They contain a small amount of americum-241,which gives out alpha particles. The
alpha particles ionise the air which is detected by a sensor. Smoke entering the
detector blocks the alpha particles. This makes the sensor trigger a loud alarm
to alert people to the fire.
TRACERS IN MEDICINE – ALWAYS SHORT HALF LIFE EMITTERS;
Certain radioactive isotopes can be injected into people and their progress around
the body can be followed using an external detector. A computer converts the
reading display showing where the strongest reading is coming from. A wellknown example is iodine-131, which is absorbed by the thyroid gland just like
normal iodine-127, but it gives out radiation which can be detected to indicate
whether the thyroid gland is taking in iodine as it should. All isotopes which are
taken into the body must be GAMMA or BETA emitters, so that the radiation
passes out of the body – and they should only last a few hours, so that the
radioactivity inside the patient quickly disappears. They should have a short
half-life
RADIOTHERAPHY – USING GAMMA RAYS;
Since high doses of gamma rays will kill all living cells, they can be
used to treat cancers. The gamma rays have to be directed
carefully and at just the right dosage so as the kill the cancer cells
without damaging too many normal cells. However, a fair bit of
damage is inevitably done to normal cells, which makes the
patient feel very ill. But if the cancer is successfully killed off in the
end – its worth it.
STERILISATION OF FOOD & SURGICAL INSTRUMENTS – GAMMA RAYS
Food can be exposed to a high dose of gamma rays which kill all
microbes, keeping the food fresh for longer. Medical instruments
can be sterilised in just the same way, rather than by boiling them.
The great advantage of irradiation over boiling is that it doesn’t
involve high temperatures, so things like fresh apples or plastic
instruments can be totally sterilised without damaging them. Te
food is not radioactive afterwards – so its perfectly safe to eat. The
isotope used for this needs to be a very strong emitter of gamma
rays with a long half-life so that it doesn’t need replacing too often
Radioactive Dating
-
The discovery of radioactivity and idea of half-life gave scientists their first
opportunity to accurately work out the age of rocks, fossils and archaeological
specimens.
- By measuring the amount of a radioactive isotope left in the sample and knowing
its half life you can work out how long the thing has been around
CARBON 14; Carbon-14 makes up about 1/10000000 of the carbon in the air. The
level stays fairly constant in the atmosphere. The same of Carbon-14 is also
found in living things. However, when they die the C14 is trapped inside the
thing and it gradually decays with a half life of 5730 years. So, by measuring the
proportion of C14 found in some old axe handle, burial shroud you can calculate
how long ago the item was living.
THE RESULTS FROM RADIOACTIVE DATING AREN’T PERFECT BECAUSE;
- The level of C14 hasn’t always been constant – cosmic radiation, climate change
and human activity all effect it. So, scientists are adjusting their calibration tables
- Not all living things can act as we expect. E.g. Some plants take up less C14
- Scientists cannot be 100% sure the sample hasn’t been contaminated
- Measuring error – the proportion of C14 is unlikely to exact. So its better to use
technology as it makes less mistakes
Radioactivity Safety
RADIATION HARMS LIVING CELLS;
• Alpha, beta and gamma radiation enter living cells and collide with molecules
• These collisions cause ionisation which damages/destroys the molecules
• Lower doses tend to cause minor damage without killing the cell
• This can give rise to mutant cells which divide uncontrollably – THIS IS CANCER
• Higher doses tend to kill cells completely which cause radiation sickness if a lot
of the bodies cells all get killed at once
• The extent of harmful effects depends on; how much exposure and the energy
and penetration of the radiation
OUTSIDE THE BODY – Beta and gamma radiation are more dangerous here as they
can get inside organs where as alpha can’t penetrate the skin
INSIDE THE BODY – alpha sources do all their damage in a very localised areas there
are more damaging here as they cant escape where as beta and gamma rays
pass straight out.
IN THE SCHOOL LABORATORY;;
1. Never allow skin to contact with a source.
Always handle with tongs.
2. Hold the source at arm’s length to keep it as far
from the body as possible
3. Keep the source pointed away from the body
and avoid looking straight at it
4. Always store the source in a lead box and put it
back as soon as the experiment is over
When Marie Curie discovered the radioactive properties of radium in 1898,
nobody new anything about its dangers. People were fascinated by radium – it
was used in medicines and to make luminous paint. You could buy everyday
products made using this pain e.g. Glow in the dark watches.
However by the 1930’s people were starting to link health problems to radiation –
many wat dial painters developed cancer as a result of exposure to radium.
More recently, we’ve learnt a lot about the dangers of radiation.
Splitting the Atom
Einstein predicted E=mc². His predictions were confirmed over 30 years late by the
development of nuclear fission;
THE CHAIN REACTION;
- A slow moving neutron is fired at the uranium-235 atom. The neutron is absorbed by
the nucleus – this makes the atom unstable and causes it to spilt,
- When the U-235 atom splits it forms two new lighter elements (daughter nuclei).
There are lots of different pairs of atoms that uranium can spilt into, e.g. Krypton-91
and barium-143, but all these new nuclei are radioactive because they have the
‘wrong’ number of neutrons
- Each time a uranium atom splits up it also spits out 2 or 3 neutrons, which can hit
other uranium nuclei, causing them to split also and so on and son on. This is a chain
reaction.
- Each nucleus splitting (called a fission) gives out a lot of energy. Going back to
Einstein's theory, this energy comes from the fact that the fission products have
slightly less mass than the original nucleus – the ‘lost’ mass is converted to energy.
Each fission gives out a lot more energy than you release much more energy than you
get with a chemical bong between two atoms. Nuclear processes release much more
energy than chemical processes do. That's why nuclear bombs are much better than
bombs which rely on chemical reactions
 Nuclear Fission can happen with uranium and plutonium atoms
THE PRODUCTS OF NUCLEAR FISSION ARE RADIOACTIVE;
The daughter nuclei produced by nuclear fission have too many
neutrons to be stable. To become more stable they turn a neutron
into a proton – giving off a beta particle at the same time.
This process continues, creating a decay series until you get a stable
nucleus. Decay series are drawn with arrows between each
isotope in the series and show what particle each isotope emits
when it decays
Nuclear Power Stations
Nuclear power stations are powered by nuclear reactors. In a nuclear reactor, a
controlled chain reaction takes place in which uranium atoms split up. The
fission of an atom of uranium releases loads of energy in the form of thermal
energy (heat). This heat is used to boil water to drive a steam turbine
Inside a Gas-Cooled Nuclear Reactor
1) Neutrons are injected into the reactor to ‘kick-start’
the fission process
2) The daughter products then collide with other atoms,
causing the temperature in the reactor to rise
3) Control rods often made of born limit the rate of
fission by absorbing excess neutrons
4) A gas, typically CO₂ is pumped through the reactor to
carry way the heat generated
5) The gas is then passed through a heat exchanger,
where it gives it energy to water – this water is heated
and turned into steam, which turns a turbine
generating electricity
Pros and Cons of using Nuclear Power;;
 Fossil fuels (coal, oil, gas) all release CO₂. This adds to the
greenhouse effect and global warming. Burning coal and oil also
releases sulphur that can cause acid rain. In terms of emissions like
this nuclear power is very clean
 The main environmental problem is with the disposal of waste. The
products left over after nuclear fission are generally radioactive –
so they can’t just be thrown way.
 It carries the risk off leaks from the plant or major catastrophes like
Chernobyl
 Building a nuclear plant bring skilled jobs to the area and support
industries around it.
 Nuclear fuel like uranium is cheap but the overall cost of nuclear
power is high due to the cost of the power plant and final
decommissioning. Dismantling a nuclear plant safely takes decades
Nuclear Fusion
• Its the opposite of nuclear fission
• In nuclear fusion, the light nuclei like hydrogen combine to create larger
nucleus
• Fusion releases a lot of energy (more than fission for a given mass) all the
energy released is stars comes from fusion. So people are trying to
develop fusion reactors to make electricity
• Fusion doesn’t leave behind a lot of radioactive waste and threes plenty
of hydrogen to use as fuel
• The big problem is that fusion only happens at really high densities and
temperatures (about 10000000°C)
• No material can withstand that kind of temperature – it would just be
vaporised – so fusion reactors are really hard to build. You have to contain
the hot hydrogen in a magnetic field instead of a physical container
• There are a few experimental reactors around at the moment, the biggest
one being JET (Joint European Torus) but none of them are generating
electricity yet. It takes more power to get up to temperature than the
reactor can produce
Cold Fusion
A new scientific theory has to go through a validation process before its accepted. This
means making the research results public – usually in a scientific journal such as
Nature, so that other scientists can repeat the experiments. If lots of scientists get the
same results, the theory is likely to be accepted. Cold Fusion hasn’t been accepted;
•
Cold fusion is nuclear fusion which occur at around room temperature – rather than
at millions of degrees Celsius
•
In 1989, 2 scientists – Stanley Pons & Martin Fleischmann reported to a press
conference that they had succeeded in releasing energy from cold fusion using a
simple experiment. This caused a lot of excitement – cold fusion would make it
possible to generate lot of electricity, easily and cheaply. However many scientists
were sceptical believing that fusions is only possible at very high temperatures.
•
After the press conference, other scientists tried to repeat the experiment. But few
managed to reproduce the results reliable. When a group at MIT (Massachusetts
Institute of Technology) discredited the theory the feeling against cold fusion was so
strong that scientific journals fused to publish papers on it
•
Despite all the setbacks, there is still funding available for cold fusion research and
Pons and Fleischmann's results have actually been repeated many times now –
although not reliably enough to the theory to be accepted
Static Electricity
Build-up of Static is Caused by Friction; When two insulating materials are rubbed
together, electrons will be scraped off one and dumped on the other – This leaves a
positive static charge one and a negative static charge on the other. Which way the
electrons moves depend on the two materials involved. Electrically charged objects
attract small objects placed near them. Classic examples are polythene and
acetate; electrons move from the duster onto a polythene rod leaving the duster
with a positive charge and the rod with a negative charge. Electrons move from the
acetate rod onto the duster leaving the rod with a positive charge and the duster
with a negative charge.
Only Electrons Move; Both positive and negative charges are produced by the
movement of electrons. But the positive charges do not move. A positive static
charge is always caused by electrons moving away elsewhere.
Like Charges Repel, Opposite Charges Attract; Two things with opposite electric
charges are attracted to each other. Two things with the same electric charge will
repel each other. These forces get weaker the further apart the two things are.
As Charge Builds Up, So Does the Voltages = Sparks; The greater the charge on an
isolated object, the greater the voltage between it and the Earth. If the voltage gets
big enough, a spark will jump across the gap. High voltage cables can be dangerous
for this reason and Big Sparks have been known to leap from overhead cables to
earth.
Static Electricity Being Helpful;
Fingerprinting; Static can be used by forensic scientists to take fingerprints – a fine
dust is brush over surfaces which sticks to the ridges of a fingerprint. This dust
can the be picked up sing an electrostatic dust lifter. A thin film is given a high
positive charge and pressed down onto the dust. The tiny dust particles are
attracted to the charged surface and leave an impression of the print on the film.
This can also be used to pick up dusty footprints and tyre marks
Laser Printing; Using coded information from a computer, a laser beam scans across
the positively charged rotating drum. Where the laser hits the drum the
electrical charge is removed. This creates an image of the page on the drum.
Positively charged toner is then applied to the drum. This black powder clings to
the discharged areas of the drum and is repelled to from the rest of it. As the
drum rolls over the negatively charged sheet of paper picks up the image. The
paper passes through the fuser – heated rollers which melt the powder from a
permanent print.
Static Electricity Being A Little Joker;
Clothing Crackles; When synthetic clothes are dragged over (like in a tumble dryer or
over your head) each other electrons get scraped off leaving static charges on
both parts and that leads to the inevitable attraction – they stick to each other
and little sparks as the charges rearrange themselves
Car Shocks; Static charge can also build up between your clothes and the synthetic
car seat. Then, when you get out of the car and ouch the metal door it can give
you a real buzz. Some cars have conducting rubber strips which hang down
behind the car. This gives a safe discharge to earth
Static Electricity Being Dangerous;
Lightning; Rain drops and ice bump together inside storn clouds, knocking off
electrons and leaving the lower clouds negatively charged. This creates a huge
voltage and a big spark
The Aircraft Fuelling Nightmare; As fuels flows out of the fuel pipe the fuel gains
electrons from the pipe, giving it a negative charge and the pipe a positive
charge. The voltage between the fuel and the pipe can easily lead to a spark,
which could ignite the fuel...BOOM. The solution is too connect the plane fuel
tank to earth with a metal strap so that the charge is conducted away, instead of
building up OR connect the fuel tanker and the plane by a metal conductor
Variables
INDEPENDANT; thing you change
DEPENENDANT; thing you measure
CONTROLLED; things controlled