Cars are designed to slow people down over a longer time when they crash (longer for change in momentum):
- Crumple Zone – bonnets take a long time crumple
- Seat Belts – stretch so there is less force acting on chest
- Air bags – slow you down
Roller coasters and Relativity
Energy is always transferred; Food enables us to move (Chemical → Kinetic)
Work Done = Force x Distance
Kinetic Energy (moving) = ½ Mass x Velocity²
Energy’s unit is Joules.
Potential Energy = Mass x Grams x Height
Energy Conservation – Using other energy to save fossil fuels and save the world.
Principle of Conservation of Energy – energy can never e created or destroyed: only converted from on to another.
Energy is only useful when you transfer it from one form to another.
When something falls, the potential energy is converted to kinetic energy:
Kinetic Energy gained = Potential energy lost
Power is the rate of doing work. So Power = Work done / Time Taken
Power measured in watts or j/s (same thing)
Circular force – velocity is always changing (accelerating). A force acting toward the centre of a circle is called a centripetal force.
Putting Radiation to Use
Ionising – losing/gaining electrons, three types:
- Alpha (Helium Nuclei) – Big, Heavy and Slow Moving, + Charge – Strongly Ionising: Doesn’t Penetrate far into materials, stopped by PAPER
- Beta – Small, negatively charged, in between, moderately ionising and penetrating, stopped by ALUMINIUM
- Gamma – weakly ionising but can penetrate far into a material, stopped by LEAD
Background radiation is all around us from:
- Everything; from unstable isotopes: food, buildings and rocks
- Space: Cosmic rays from the sun (earth atmosphere protects us from that)
- Humans; Errors like nuclear explosions and waste
Background radiation can change depending where you are:
- High altitude: you are closer to cosmic rays
- Underground mines: because of the rocks down there
- Homes; some are built over or by granite which releases radiation
Radon gas causes: lung cancer (ventilation systems can stop)
Atoms: nucleus has most of the mass (still tiny) and protons and neutrons
Alpha has 2+ charge
Beta has 1- charge
Gamma waves have no charge
Isotopes – different forms of same element (different amount of neutrons), only a few stable ones. Unstable ones decay into other elements (and give out radiation on the way)
You can tell when the unstable isotope atoms will decay, it’s random. Nothing affects decay.
Radiation decreases over time.
Half-life is the time taken for half of the reactive atoms to decay. Can’t do full because it takes too long.
If half life falls quickly it has short half-life.
How to work out half-life: Atom A’s activity is 500cmp (counts per min). 1 hour later it’s 125cmp
This shows it has two half-lives in hour, so 1 half life is 30mins
Half-life graphs always go down in a curve. G-M tube and counters are used to measure half life over time (multiple readings).
You need to take away background radiation from every reading.
Ionising Radiation Uses:
- Smoke detectors: alpha radiation placed next to electrodes a current flows, if smoke appears it absorbs radiation and stops current which sets off alarm
- Tracers in Medicine – check if things around the body are taking things as they should be. There will be a strong reading where the body isn’t doing something it should. Never use Alpha rays for body (they have longer half lives)
- Radiotherapy – high dose of gamma rays kill humans cells, so they can kill cancer cells.
- Food and medical supplies are exposed to high dose of gamma rays which kills of microbes. Doesn’t use temperature which means it doesn’t damage food. Gamma rays need to have long half life so it doesn’t need to do it too often.
Knowing half life and how much radioactive isotope left in specimen you can work out how long it’s been around.
Carbon-14 makes up 1/10 000 000 of anything but when it dies, it starts to decay. It’s half life is 5730 years.
So if a body was found with 1/80 000 000 Carbon-14 you could work out how long it was alive by:
1/10 → 1/20 → 1/40 → 1/80 : Shows it has three half-lives. 3 x 5730 = whatever
Carbon dating is uncertain because:
- Assumes same amount of carbon in air
- All living things take in same proportion of C-14
- Substances haven’t been contaminated by recent carbons
Beta and Gamma causes most damage outside body because it can damage cells inside
If alpha gets in it can damage body a lot because it collides a lot with cells.
Precautions that should be taken with radioactive things:
- No skin contact (tongs)
- Arms length – keep away from body
- Don’t look right at it
- Use lead box
Power of Atoms
Einstein said that mass is a form of energy. Nuclear fission is proof of that.
Nuclear Fission – The splitting up of uranium atoms. Uncontrolled releases of energy = bomb.
Controlled (chain reaction):
- Slow moving neutron is fired at uranium.
- The neutron gets absorbed
- This makes the uranium unstable which causes it to split
- The uranium also gives off neutrons that can be used to hit other uranium particles (back to 1)
The lost mass (the neutrons) are converted into energy which means Einstein was right.
Nuclear mass gives out much more energy than chemical ones: why their used in bombs.
The daughter nuclei (the result of the splitting in uranium) is radioactive and they are not stable (too many neutrons. They become stable by transforming neutrons in protons (in the process beta particles are given off). They keeping doing this until they become stable (called decay series)
Nuclear Power Stations work like this:
- In nuclear reactors, controlled chain reaction takes place where uranium is split up, this gives off a lot of heat energy.
- The heat is used to boil water to drive a steam turbine
-
Nuclear (Uranium Reactor) → Heat (Boiling Water → Kinetic (Turbine) → Electrical (Generator)
Inside Reactor: Neutrons added to start splitting, daughter nuclei collide with other atoms causing temperature to rise, the Co2 which is pumped in carries away the heat energy which is used to turn water to steam (which powers the turbine)
Nuclear Power Advantages:
- Clean; doesn’t release as much C02 into environment (which stops green house effect)
- Can create a lot of jobs in area
- Nuclear fuel is cheap (uranium)
Nuclear Power Disadvantages:
- Overall cost is high (building power plants and getting rid of waste)
- Waste is radioactive so it could damage human cells if leaked (have to put deep in the ground with metal containers and surrounded with concrete
- Dismantling nuclear plants takes decades
Nuclear Fusion – the joining of small atomic nuclei. Opposite of Fission; it combines two light nuclei to make larger nucleus. Fusion makes more energy than fission. Fusion doesn’t leave much waste behind and hydrogen (by-product) can be used as fuel afterward.
Problems: Fusion needs temperature of 10 000 000°C and really high densities. No material can stand that temperature so reactors are hard to make. You also have to keep the hydrogen (used as neutrons that are added) in a magnetic field. More power needed to produce conditions than reactor can make.
Static electricity is charges that are not free to move about. This causes them to build up in one place and often ends with spark or shock when they do move.
Static electricity is caused by friction: when two insulating materials rub eachother; electrons will scrap off one and go to another. This leaves a + and – on each one.
Positive charges can not move. They are created by electron going elsewhere.
Opposite charges attract. The larger the build of charges, the larger the shock/spark.
Good uses of SE:
- Fingerprinting: fine dust is brushed over ridges of finger print (gives an image of finger print) then electrostatic dust lifter is used to lift dust and then a highly charged film pressed on to dust which are attracted to it. This leaves an impression on the film
- Laser Printing: A laser passes over the drum inside a printer, giving it a pattern of charged dots. The toner picks up the drum whenever a dot is there. The dots of toner then put onto the paper to make up words and pictures.
When synthetic clothes are dragged over eachother, they static charges on both parts which causes a attraction. Sparks occur when they rearrange themselves. Also happen with car seats but shock happens when you touch metal outside.
Lighting – rain drops and ice bump together which knocks of electrons. The electrons go to the bottom and then they build up and a huge voltage is given off.
Aircraft Fuelling: when planes are being fuelled, the fuel gains a – charge from the pipe and the pipe gets + charge which could explode. You have to attracted metal strap so the electrons are conducted away.
