# Physics Unit 2

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• Created by: Lottie_C
• Created on: 05-04-16 13:37
Friction
wastes energy by transferring to heat, provides grip, slippy surface has less friction, resistive force
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resultant force
if in direction of motion causes acceleration, if against direction causes deceleration, if acting on stationary body it will accelerate in direction of resultant force
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velocity
speed of body in given direction
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stretching force
spring stops stretching when weight equals tension, if mass added stretches more
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drag forces
air/water resistance, act against motion, caused by air/water particles hitting object as it moves past, increases if object moves faster/has bigger surface area
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elastic potential energy
if apply force to elastic object it may stretch, if force removed goes back to original shape
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thinking time reaction
time taken between spotting hazard and pressing brakes
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thinking distance
distance travelled in reaction time
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stopping distance
total distance travelled from spotting hazard to stopping
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braking time
time taken to stop vehicle after brakes pressed
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stretching a spring
spring may overstretch if too heavy force, doesn't go back to original shape, past limit of proportionality
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mass
measure of amount of matter a body contains, kg
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weight
force of gravity acting on mass, newtons
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conservation of momentum
in any collision momentum is conserved, total momentum before is same as total after, provided no external forces act
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extension
stretched length - original length
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work done
energy can be transferred by doing work, work done when force causes body to move through distance
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rebound
2 objects that bounce off one another
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explosion
2 objects not moving push apart and move in opposite directions
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coalesce
2 objects join together
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factors affecting stopping distance
drunk, drugs, distraction, speed, mass of car, ice, worn tyres
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distance time graphs
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velocity time graph
acceleration is vertical/horizontal, distance is area under graph
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regenerative braking
makes use of energy produced, stores energy in battery rather than wasting it
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crumple zones
crumple up on impact, increase the impact time, decreasing the force produced by the change in momentum
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side impact bars
strong metal tubes in car doors, direct kinetic energy away from passengers
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seat belts
stretch slightly, reduces forces acting on chest, some kinetic energy absorbed by seat belt stretching
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air bags
slow you down more gradually, prevent you from hitting hard surfaces
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charge
given to insulating molecule by rubbing them
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rules of electrostatics
opposite charges attract, like charges repel, charged objects attract neutral objects
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earthing and discharge
object will charge up providing its not connected to earth by conductor
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earth connection
when you connect an object to ground with conductor
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What will happen if a person is the earth connection?
They will get an electric shock
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What will happen if the dome is highly charged?
Large PD between dome and earth so it pushes electrons through the air as sparks
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Discharging a positive object
extra electrons pulled up from earth to neutralise charge
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insulating electrons
bound to atoms so charge cannot flow to Earth
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gold leaf electroscope
if positive rod, electrons move up to cap, gold leaf left positive so repel and gold leaf sticks out. if negative rod used electrons pushed down stem, gold leaf repels and sticks out
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van de graaf generator
frictions rub electrons onto belt, electrons carried up, electrons rubbed off onto dome, dome becomes negatively charged
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perspex
friction transfers off perspex onto cloth making perspex positive
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polyethene
friction transfers electrons on to polyethene from cloth making polyethene negative
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PD/voltage
gives charges energy which makes them produce more velocity
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restricting current
resistors introduce certain amounts of resistance to restrict current and protect them
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why is resistance is opposition?
more resistance reduces current, all components have resistance
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Diode
a component that will only conduct in one direction, used to prevent reverse currents
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Thermistor
as temperature is higher, resistance is lower, use for thermostat
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LED's (light emitting diodes)
conducts electricity to light up when forward biased, last longer and are cheaper, use less energy, TV standby, car lights
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LDR's
as light intensity is higher, resistance is lower, use for street light which switch on automatically when its dark
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Variable resistors
as current decreases bulb gets dimmer, use for dimmer switch/ volume control
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series circuit
all components on single loop, current same through every component, PD shared, components with bigger resistance have a bigger share of PD
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Parallel circuit
more than 1 circuit loop, PD same for every component, current splits between loops
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choosing correct fuses
find normal current needed, choose fuse with next highest current rating
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problems with fuses
need to be replaced, slow to respond
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quick to respond, safer as they switch off quicker, reusable
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why should RCCB's switch off if input and output different?
current thats not returning could be going somewhere else e.g. electronic shock
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RCCB's
residual current circuit breaker, trips if current changes (current input is different to output current), respond quickly, easily switched back on
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DC
direct current, batteries, current which flows in 1 direction only
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AC
alternating current, mains electricity, constantly changing direction, 50Hz used for UK Mains
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Safe wiring
all bare wires must be screwed in place, no wires 'whiskers' visible, live wires must be connected to fuse
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3 pin plug
1 is earth pin, safety feature, 0V unless fault, yellow/green. 2 is neutral pin, PD around 0, blue. 3 is live pin, high alternating current, PD 230V, red.
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Triple core wires
3 copper wires (conductors), made of thin copper threads, outside covered with plastic
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isotopes
different form of same element, same number of protons, different number of neutrons
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ionisation
atoms can gain/lose electrons to form ion. Alpha, Beta, Gamma are types of ionising radiation
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the higher the radiation dose, the more at risk you are
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Alpha
2 neutrons and 2 protons (helium), mass of 4, charge of +2, least penetrating, strongly ionising, blocked by paper
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Beta
moderately penetrating/ionising, charge of -1, nearly no mass, an electron, blocked by aluminium
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Gamma
rays, type of EM wave, very penetrating, weakly ionising, no mass/charge, blocked by lead
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outside body beta and gamma most dangerous, inside body alpha most dangerous
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Rutherford
one or two atoms bounce back from nucleus
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Half life
the radioactivity of a sample decreases over time, half life is the average time for number of nuclei in sample to half, varies
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Nuclear fission
splitting up big atomic nuclei, neutron hits nucleus so its unstable, then releases 2/3 neutrons and energy
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comes from all around us. For example air, food, rocks, cosmic rays, human activity (hospitals), radon gas
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random process, unstable nuclei are radioactive so will decay giving out alpha, beta or gamma
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## Other cards in this set

### Card 2

resultant force

#### Back

if in direction of motion causes acceleration, if against direction causes deceleration, if acting on stationary body it will accelerate in direction of resultant force

velocity

stretching force

drag forces