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# Physics P2 Topic Overview Coursework

Extracts from this document...

Introduction

As Fast As You Can

Vector quantity – they have magnitude (size/speed/unit/distance) and direction

Speed – how fast you’re going

Velocity – speed in a given direction (vector quantity)

Displacement – the distance in a given direction (vector quantity)

Speed cameras work by taking two pictures, and then used formula (speed = distance/time)

Acceleration – how quickly velocity is changing. Change speed or change in direction.

Acceleration = Change in Velocity (two units taken away from eachother)/Time Taken

Graphs: the gradient is the acceleration. Straight line is steady speed, straight line going up is steady acceleration, and curved line going up is increasing acceleration.

Balanced force means steady speed (which could be stationary object).

Unbalance force means acceleration in the side that has the most force acting on it.

When something has no force applied to it, it will stop because of friction. (If you don’t accelerate a car it will stop eventually). To avoid resistance or drag from things they must be streamlined so that the resistance can travel over.

Terminal Velocity – maximum speed that something can reach with that force applying on it. Example: when car starts, it has less resistance, as time goes by: resistance equals the acceleration which means the car has reached its terminal velocity.

Rules:

• Balanced forces: it’ll stay at same speed
• Unbalanced force (resultant force): object will accelerate in direction of force
• Bigger force; more acceleration. Bigger force needed to move big mass

Force = Mass x Acceleration                 Example: Forced needed for 12kg at 5m/s is 60N

If you apply a force on a wall if exerts the same force on to you.

The distance a car needs to stop is calculated by: Thinking and Braking Distance.

Thinking distance:

• Speed
• Mentality; drugs, tired, alcohol
• Visibility; rain, snow, dirty windows, darkness

Breaking Distance:

• Speed
• Weight; more force must be applied to stoop a heavy car
• Brakes; shit breaks take longer to stop
• Grip; road surface, weather, tyres: if grip is shit it’ll take longer to stop

Momentum (kg m/s) (vector quantity) = Mass (kg) x Velocity (m/s):

More mass/velocity, the more momentum: momentum is force of something hitting something else. Force causes change in momentum.

Force acting = Change in Momentum (kg m/s) / Time Take for Change

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
...read more.

Middle

Alpha (Helium Nuclei) – Big, Heavy and Slow Moving, + Charge – Strongly Ionising: Doesn’t Penetrate far into materials, stopped by PAPERBeta – 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
...read more.

Conclusion

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.

...read more.

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