Download Physics 2a Revision - The Thomas Cowley High School

Physics 2a Revision
1. Speed, velocity and acceleration
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Speed(m/s) = distance travelled (m)
Time taken (s)
The steeper the line on a distance-time graph, the greater the speed
Velocity is speed in a given direction
Acceleration = change in velocity(m/s)
time (s)
The slope of the line in a velocity-time graph represents acceleration
The area under the line represents the distance travelled
Transport issues.
Stopping distance = thinking distance + braking distance
Braking distance is distance vehicle travels under braking force – affected
by speed, road conditions, maintenance of vehicle,
Thinking distance, is distance travelled before driver reacts- again speed
affects distance as does alcohol, drug, tiredness of driver
You should be able to explain the need for congestion charges , tax on fuel,
Speed cameras
2. Forces
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Forces are measured in Newton’s (N)
When two objects interact they exert equal and opposite forces
Resultant force is the effect of two or more forces on an object.
If an object is stationary or moving at a constant speed the forces are equal
or balanced.
If an object is accelerating or decelerating then there is resultant force
acting upon it.
(Resultant)Force = Mass X acceleration
Mass is measured in Kg
Weight is the effect of gravity on the objects mass and measured in Newton’s
Weight = Mass X gravitational field
Gravitational field on Earth = 10N/kg. The moons gravitational field is 1/6th that
of earth
Falling objects. An object falling freely accelerates at 10m/s2
As an object accelerates, the frictional forces (air resistance) increase until
both forces are equal. The objects speed then becomes constant. Terminal
Velocity
3. Work & Energy
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Work done (J) = energy transferred
Work done(J) = force (N) X distance moved(m)
Elastic potential = energy stored in an elastic object( Elastic objects regain
shape after being stretched or squashed)
Gravitational potential = force (N) x Distance raised (m)
Kinetic energy = ½ mass X speed2 Higher
Momentum has size and direction.
When two objects push each other apart, they move apart with equal and
opposite momentum
 Momentum (Kg m/s) = Mass(kg) x Velocity (m/s)
 Basically -The Heavier the lorry and the faster it is travelling the greater
force it will exert in a crash (i.e. the greater its momentum)
 When ever objects interact the momentum is conserved.
 Car safety. Crumple zones in cars are designed to lesson the force of
impact. They increase the impact time and lesson the force exerted
 Force = change in momentum (kg m/s)
Time (s)
 You should be able to explain how air bags, car seat belts & side impact bars
work.
4. Electrical charges
You should already know the structure of a n Atom and the charges of the sub
atomic particles
 Static electricity. Caused when electrons are “rubbed off” one material onto
another. Materials losing electrons becomes positively charged, the other
negatively charged. Like charges repel, unlike attract.
Uses – Painting cars/bicycle frames. Photocopiers, air fresheners, reducing
air pollution. You need to be able to explain uses and also the Possible dangers of
static when –Refuelling planes, refuelling car at petrol station, using
Computers and how these are overcome.
 Moving charge . Current is rate of flow of charge. Metal objects can only
hold charge if they are isolated from ground. Earthed by connecting to
ground.
5. Electric circuits.
 Know Symbols for Cell, Battery, switch, diode, ammeter, voltmeter, lamp,
fuse, heater, fixed and variable resistors.
 Draw circuit diagrams with ammeters (series) and voltmeters (parallel)
 Ohms law
Potential difference (Volts, V) = Current (Amperes A) X Resistance(ohm Ώ)
 Resistance - measure of how hard it is for current to flow through a
component. Current through a Resistor at constant temperature is directly
proportional to the PD across the resistor (A / Straight line graph).
Filament lamp – resistance increases with temperature. Diode – forward
resistance low; reverse resistance high. Thermistor resistance decreases as
temperature increases. LDR resistance decreases as light intensity
increases.
 Series circuits. Current same in each component. PD of each added to give
total PD of circuit. Resistance of each added to give total for circuit( R1 + R2
= Total)
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Parallel circuits. Pd is same across each component. Total current = sum of
currents through each component. Bigger the resistance the smaller the
current.
6. Alternating current.
 Mains electricity - Repeatedly reverses is direction. Live wire is
alternatively positive and negative every cycle. Neutral wire 0 volts.
 Plugs- Cables – have 2 or 3 insulated copper wires surrounded by outer layer
of flexible plastic. You must be able to draw and label a plug and know
correct colours.
 Fuses. Thin wire that melts if too much current flows(breaks circuit) Circuit
breaker - electromagnetic switch that opens and trips circuit if too much
current flows. Fuses should be of correct rating to prevent fires as cables
overheat.
 Power (watts, W) = Energy transformed (J)
Time (s)
 Watts = Current X Voltage. This can be used to calculate the current an
appliance uses. Voltage to homes = 230V.
 Charge. Charge (columbs C) = Current X time. When charge flows a resistor ,
electrical energy transferred as heat.
 Energy transferred(J) = PD X Charge (C)
7.Nuclear reactions.
 Isotopes are atoms of an element which have different numbers of
neutrons ( so mass number different)
 Decay. 3 types - Alpha large particle consisting 2 protons & 2
neutrons.(loses 4 mass units ). Beta β neutron in nucleus changes into a
proton and an electron ( electron is emitted). Gamma. γEnergy wave
produced after an Alpha or Beta particle emitted.
 Background radiation – from rocks and space. Half life time taken for half
material to decay.
 Discovery of atom structure – by scattering experiments.( HIGHER only)
 Fission – Uranium 235 or plutonium 239 nucleus splits . Chain reactions
occur as fission causes other atoms to split. Nuclear reactors –control rods
absorb surplus neutrons, Water used to keep fuel rods cool.
 Fusion – Two nuclei forced close enough to join. Energy released ( This is
what happens in stars! New elements formed) Fusion reactors – would
release enough energy to meet all our energy needs – scientists still working
on it though!
Higher
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