speed and velocity
SPEED & VELOCITY
speed: is how fast your going.
velocity : is how fast your going in a particular direction.
velocity = displacment / time taken
acceleration is how quickly the veloctiy is changing . this change in velocity can be a change in speed or a change in direction or both
acceleration = changein velocity /time taken
units for acceleration is m/s ( squared )
friction and terminal velocity
friction always slows things down
friction always acts on the opposite direction if movement.
resistance or drag : from fluid and air
to reduce drag from fluids the shape of the object should be streamlined.
terminal velocity: is when the resistance force is equal to the acceleraion force.
forces are a push or a pull ..
the movement of an object depends on the force acting on it. th balance of these forces is called the resultant force. e.g. moving car has the forces acting upon it which effect its movment .
force and acceleration
if the forces on the object are all BALANCED then the the object will keep moving at the same speed in the same direction .
if the forces are UNBALANCED then the object will move in the same direction of the force.
1. the thinking distance is the disance travelled by the vechile in the time it takes a driver to react
2. the braking distance is the distance the vechile travels under the brakng force.
3. the sopping distance = the thinking dstance + the braking distance
when the resistive force is bigger than the drving force , the car is deaccelerating. An unbalnaced force acts on the car causing the car to slow down... i.e deaccelerate.
work and kenitc energy
work= Force x distance
when aforce moves an object ,energy is transfered and the work is done.
work and energy is measured in joules (j)
kineic energy : energy of movement
kinetic energy :1/2 x mass x velocity (squared)
kineic energy depends on both mass and the speed more it wieghs and the faster it is going , the better the kinetic energy will be.
electrical and potential energy
cells batteries , generate all transfer energy to compontents in the circuit
1.when an electrical charge goes through a change in the voltage, energy is transfered.
2. energy is given to the change at the power source to raise it through a voltage.
3) the charge is given up when it passes through compotents in the circuit .
electrical energy : voltage x current x time .
energy transfer is rarely 100% efficant , there will almost always be wasted heat , noise energy etc.
object lifted above the ground gains potential energy (PE)
often called GPE
additional hieght gives it the potential to do work when it falls.
potential energy (j) =mass (kg) x accelertion pf free fall (N/KG) change in hieght (h)
gravity on earth is 10 (N)
power is a rate at which work is done. it's the work done per second, its measured in WATTS. one watt means one joule of energy is transfered per second. work done is the energy transfered , therefore
power= workdone / timetaken
in an object moving in a circular motion at a constant speed its velocity is constantly changing direction -since the velocity is changing direcion the objs is accelerating .
-acceleration - the change of velocity per sec
-centripetal - towards the center of the circle.
centripetal (N) = mass (kg) x speed (squared) / radius(m)
everything moving in a circle needs a force to ensure it carries on in a cricle. the velocity is changing all the time as its always changing direction .
it is also accelerating so his means it has an overall resultant force
the faster the object is moving , the bigger the centripetal force has to be. the larger the object is , the bigger the centripetal force has to be . the smaller the circle he larger the force has to be (to keep it turning)
at (1) the carriage has the most GPE
at (2), the potential energy has been converted into kinetic energy , therefore this is where it has the most kinetic energy ,but the least potential energy.
at (3), it has accelerated again , it will have GPE
at (4) , it will lose potentail energy once again as it will have been converted into kinetic energy.
when working out the maximum speed or something on a roller coaster , think of the potential energy it has lost and the kinetic energy it has gained.
a radioactive nucleus is unsatable and will emit radiation
there are 3 main types :
-only travels a few centimeters in air
- stopped by a thin sheet of paper
ionising radiation (continued)
-penertares card or several shees of paper
-stopped by a 3mm thick sheet of aluminium or other metal .
reduced signifficantly by a thick lead sheet or blocks of concrete.
ionising radiation (continued)
ionising radiation - radiation that has enough energy to break molecules or atoms into charged particles called ions.
ionistaion : the moleculesor atoms lose elecron.
after ionisation the ions can then take part in chemical reactions -->ionsing radistion damages living cells
it kill/damages thier DNA in the cell so that the cells mutates into cancer cell, which then grows inan uncomfortable manner.
electrons fly around the edge .. protons and nrutrons make up the nuclei
1. atoms are made up of protons, neutrons and electrons.
2. protond and electrons have equal and opposite electric charge , protons are positivily charged and electrons are negativly charged.
3. atoms are arranged in the peridoic table in order of thier atomic number.
atomis structure (continued)
4. neutrons have no electric charge , they are neutral
electron : -1
neutrons : 0
radiation is all around us and most of the tme we dont even know about it.
background radiation can form :
naturally unstable isotopes all aound us :-in foos, in the air , in building materials and in rocks betneath our feet.
form space : known as cosmic rays . they mostly come form the sun . luckily he atmosphere protects us from most these rays. the earth magnetic field also deflects cosmic rays.
radiation due to human activity . however this make up only 1% of the total back ground radiation .
background radiation (continiued)
the level of the radiatuion depends on where you are .it is hightest at :
-underground in mines
-certain understand ground rocks .
the radiactivity of a sample always decreases over time.
the problem with trying to measure the half -life is that teh activity never reaches zero so we have to use the idea of half life to measure how quickly the activiy drops off.
half life is the time takien the half of the radioative atoms to decay .
a short half life means teh activity falls quickly , because lots of nuclei dont decay quickly .
a long half life means the activity falls slowly , because most o teh nuclei dont decay for a long time.
half - life
to work out the half life of something half it's inital count until you get to the figure mentioned , and then work out the time interval in between each half life .
uses of radiaion
some detecors (uses a weak souece of alpha radiation )
there is a source measuring the radiation -smoke stops radiation
traces in the medicine (uses gamma rays )
swallowed by patients , we then trace it around the body
we use this information to tell us differnet things (are organs working properly )
radioactive dating is looking at how radioactive something is , and then works backwards to see how old it is.
radioactive saftey is important as i can be very harmful it cab cause cancer. the extent of damage depends on the expousre levels and type of radiation
outside the body .. beta and gamma rays are the mos dangerous
inside the body alpha is the most dangerous.
saftey includes :
hold as far from the body as possible
store in the lead box
point away from you and do not do look directly at it .
- is the splitting of the atomic particles
- the two fissionable isotopes are uranium -235 and for plutanium -239
- for fissionto occur the uranium and plutonium mus absorb a neutron
- the nucleus then splits in to two smaller nuclei and two or three neutrons and energy are realse.
- the neutrons go on to produce further fissions causing a chain reaction
- in a nuclear reactor the process is controlled
- it is the joining of atomic nuclei to from a single large nucleus
- during the process fussion energy is realeased
- nuclei approaching each other will repel one another due to thier positive charge
- to overcome this , the nuclei must be heated to very high temperature.
- this gives them enough energy to overcome the repulsion and fure
- the reaction has to take place in a contained magneic field .
nuclear fission (advantages )
- dosent produce carbon dioxide or smoke , so it dosent contribute to the greenhouse effect
- the earth ha limited amounts of coal & oil ; nuclear fision could still produce energy after coal &oil reserves become scarce.
- its very effcient , it release great amounts of energy
- its the most concentrated energy on earth so we can control it very well
- we know how to do it
nuclear fission (disadvanages )
- high starting cost because plants requires containment safeguards
- possibiltes of nuclear ,meltdown from uncontrolled reaction leads to nuclear fall out with potentially harmful effects on civilians
- produces nuclear waste, which is toxic radioactive
- waste produces can be used to make nuclear weapons , which can kill thousands and have devastating effects.
- uranium is a scarce resource -supply is esimated to last between 30-60 years
nuclear fussion (advantages)
- fussion produces helium , an abundant ge in the earths atmosphere, that wont contribute to global warming
- fusion has no dangerous by products which could be used to produce nuclear power
- the fuel for fusion reactions readily available deuterium &tritium are virtually inexhaustable
- scientists have not yet been able to contain a fusion reaction long enough for there to be a net energy gain
- harder to control than fusion
- research is now taking place abroad - so we may end up having to pay extremely high amounts of money for technology