Transcript P2 revision poster

Resultant forces
Stopping distance
• forces act in pairs, opposite
Thinking distance affected by
directions
tiredness, drugs & alcohol –
• resultant force = difference
PERSON
between 2 forces
Braking distance affected by road
• If equal and opposite = balanced =
conditions, weather, brakes –
no movement OR move at constant
CAR & ENVIRONMENT
speed
Stopping distance = thinking + braking distance
• if not equal = unbalanced =
movement in direction of bigger
force Force (N) = mass (kg) x acceleration (m/s2)
P2 Physics
Speed(m/s) = distance(m)/time (s)
Graphs
DT graph = speed.
Steeper the gradient = faster
Terminal velocity
Velocity is speed in a direction
•2 forces act on falling objects – weight (gravity) & VT graph = acceleration
air resistance
Steeper the gradient = greater acceleration
• 5 stages during parachute jump
Area under graph = distance travelled
• A – weight greater than air resistance = increase
Acceleration (m/s2) = change in velocity
in speed
(m/s) / time (s)
• B – air resistance increases but weight still bigger
= start to slow down
• C – weight = air resistance = steady speed =
terminal velocity
• D - parachute opens, increase in surface area,
air resistance greater than weight = decrease in
Energy
Work done (J) =
speed
• work done = energy transferred force (N) x distance
• E – weight = air resistance = steady speed = lower
(m)
Hooke’s law
• friction in the form of heat
terminal velocity
• Elastic objects return to original shape
• power is energy transferred in a given time
Power (W) = energy (J) / time (s)
• Extension is directly proportional to force
• gravitational potential energy is due to height.
applied
• GFS = 10 N/kg
GPE (J) = mass (kg) x gravitational field strength (N/kg) x
• force = spring constant x extension
• kinetic energy depends on mass and speed
height (m)
• too much extension – object won’t return
to original shape. Reached limit of
Kinetic energy (J) = ½ x mass (kg) x velocity (m/s)
proportionality (P)
Momentum
• the product of the mass and velocity of the object, has size & direction
• conserved in any collision
• car safety features reduce the forces due to a large change in momentum
> seat belts
> crumple zones
> air bags
• the time over which the change in momentum happens increases, so less
impact from forces
Current (A) = charge (C) / time (s)
Resistance (Ω) = voltage (V) / current (A)
Static electricity
Circuits
• Gain negative electrons
• negative electrons flow from the negative
= negatively charged
terminal
• lose negative electrons
• current – ammeter – in series
= positively charged
• current = flow of electric charge
• voltage/ potential difference – voltmeter – in • like charges = repel, opposite charges attract
• used in photocopiers & smoke
parallel
• potential difference = driving force that pushes precipitators
• can be dangerous – petrol stations
current
• series = one loop
parallel = more than one loop
• resistance = anything that slows current
• resistance varies in different components
• resistance in a LDR decreases as LI increases
• resistance in a thermistor decreases as LI
increases
Houeshold electricity
• a.c = alternating current – mains supply
• d.c = direct current – batteries
• frequency = number of waves per second = hertz. UK
supply = 50 Hz
Oscilloscope traces
• Used to determine the time period & frequency
of a supply
• frequency (Hz) = 1 / time period (s)
• time period = distance between 2 peaks
• UK 3 pin plugs
• time period = timebase x number of divisions
Charge (C) = current (A) x time (s)
 Brown = live, Blue = neutral, Green & yellow = earth
Power (W) = energy transferred (J) / time (s)
•Two-core cable = no earth wire, appliance has casing
made of insulator and no metal parts
Energy transferred (J) = potential difference (V) x charge (C)
ISOTOPES
• Fuses contain a piece of wire - if the current is too high,
atoms of the same element with
the fuse wire will melt and break the circuit.
different numbers of neutrons
Atom structure
• Circuit breakers detect a surge in current – open a switch
• protons mass = 1, charge = +1
and break circuit. Faster than fuses, but more expensive
• electrons mass = 0, charge -1
than fuses.
• neutrons mass = 1, charge = 0
• Residual current circuit breaker (RCCB) detects
• mass number = protons +
difference between live and neutral wires and cuts off
neutrons
power. Normally exactly the same current flows through
• atomic number = protons OR
the live and neutral wires
electrons
Atoms & radiation
• background
radiation comes
different source
• radiation dose
depends on dose and
occupation
Rutherford & Marsden
• Rutherford & Marsden fired alpha particles at gold foil.
• Most particles passed straight through the foil.
• Some particles were deflected slightly.
• Some were rebounded back towards the source
• CONCLUSION - all atoms consist largely of empty space with a small,
dense positive core that he called the nucleus and around this nucleus
the negative electrons were spaced out.
• Led to a change in model from plum pudding to nuclear
Radioactive decay
• Totally random process
• Unaffected by physical conditions
• 3 types:
1) Alpha decay – unstable nucleus emits an alpha particle (He
nucleus) Mass # decrease by 4, atomic # decrease by 2.
2) Beta decay - unstable nucleus changes a neutron into a
proton and emits an electron. Mass # unchanged, atomic #
increases by one.
.
3) Gamma decay – short wavelength electromagnetic
radiation given off.
Alpha and beta particles are deflected by electric and
magnetic fields – in opposite directions due to opposite
charges
Half-life
• the average time it takes for
the number of nuclei of a
radioactive isotope in a sample
to halve.
Nuclear fission
• splitting of atomic nuclei
• happens in nuclear power stations
• chain reaction – a slow moving
neutron is absorbed by a uranium or
plutonium nucleus. The nucleus splits –
releasing more neutrons which can
then hit other nuclei and cause them to
split and so on and so on ……
Nuclear fusion
• 2 lighter nuclei join together to make a larger nucleus.
• fusion releases a lot of energy
• no radioactive waste like fission
• BUT only happens at really high temperatures – difficult to hold hydrogen at high temps and
pressures