Zusammenfassung der Ressource
AQA Physics 2
- Motion
- 1.1 Distance-time
graphs
- These are used to describe
the motion of an object
- Speed (m/s) = distance (m) / time (s)
- Keywords: Speed
- 1.2 Velocity and
acceleration
- The velocity of an object is
its speed in a given direction
- If an object change direction but has the
same speed, its velocity still stays the same
- a = (v - u) / t
- Keywords: Velocity, Acceleration, Deceleration
- 1.3 More about
velocity-time graphs
- The gradient of the line on a velocity-time
graph represents acceleration
- The area under the line of a velocity-time graph
represents the distance travelled in a given time
- 1.4 Using graphs
- The gradient of a graph is an object's
speed on a distance-time graph
- The gradient of a graph is an object's
acceleration on a velocity-time graph
- The area under a velocity-time graph is the
distance travelled over that time period
- Always use the measurements
from the graph in calculations
- Forces
- 2.1 Forces
between objects
- Forces are measured
in newtons (N)
- Objects always exert
equal and opposite forces
- Keywords: Force, Newton
- An example of equal and opposite
forces is driving along a road
- 2.2 Resultant Force
- When resultant force is 0 an object is either at rest or
continues moving at the same speed in the same direction
- Keyword: Resultant force
- When resultant force is not 0, an object
will accelerate from rest, accelerate or deccelerate
- 2.3 Force and acceleration
- F = m x a
- A resultant force always causes acceleration
- The greater the resultant force,
the greater the acceleration
- Keyword: Mass
- 2.4 On the road
- If a vehicle travels at a steady speed
along the road, the resultant force is zero
- The faster the speed of a vehicle,
the bigger the deceleration needed
- Stopping distance is thinking
distance + braking distance
- Both TD and BD can be increased
through drugs and alcohol or conditions
- Keywords: Stopping distance, thinking distance, braking distance
- 2.5 Falling objects
- An object accelerates to the earth's surface at 9.81m/s²
- F = m x a
- W (N) = m x g
- If an object is on earth, g is
called gravitational field strength
- If an object falls through a fluid, the
fluid exerts a drag force on the object
- The object can only accelerate to a
certain speed, called terminal velocity
- Keywords: Weight, gravitational field strength, drag force, terminal velocity
- 2.6 Stretching
and squashing
- F = k x e (Hooke's Law)
- Keywords: Elasticity, directly proportional, limit of proportionality, Hooke's law
- Objects and materials that extend when
weight is placed on them are called elastic
- k = the spring constant in newtons per m, N/m.
The stiffer a spring, the greater its spring constant
- When an object is stressed, work is
done. This is stored as elastic potential
- 2.7 Force and
speed issues
- Reducing the speed of a vehicle reduces
the amount of fuel it uses per mile
- Reducing air resistance
also improves fuel economy
- Speed cameras are used
to discourage speeding
- Anti-skid surfaces are
used to prevent skidding
- Work, energy and momentum
- 3.1 Energy and work
- When an object moves, a
force must have been applied
- Both work and energy have the unit joule, J
- W = F x d
- Work done = energy transferred
- Work done to overcome friction is mainly
transferred into energy by heating
- Keywords: Work, friction
- 3.2 Gravitational
potential energy
- GPE is energy stored in an object because of
its position in Earth's gravitational potential
- E = m x 9.81 x h
- Power is the rate of
transfer of energy
- P = E / t
- Keywords: Gravitational potential energy, power
- 3.3 Kinetic energy
- All moving objects have kinetic energy.
The greater the mass, the faster the speed
- E = 1/2 x m x v²
- Keywords: Kinetic energy, elastic potential energy
- 3.4 Momentum
- All moving objects have momentum. The greater the
mass and velocity and the greater the momentum
- p = m x v
- Momentum is conserved whenever objects
interact, provided no external forces act on them
- Keywords: Momentum, conservation of momentum
- 3.5 Explosions
- p = m x v
- Like velocity momentum
has both size and direction
- When two objects push each other, they move apart
at different speeds if they are unequal weights
- 3.6 Impact forces
- When vehicles collide, the force of the impact depends
on mass, change of velocity and the duration of impact
- When two vehicles collide they exert
equal and opposite forces on one another
- Keywords: Impact time, crumple zone
- 3.7 Car safety
- Seat belts and air bag spread the force across
the chest and increase the impact time
- Side impact bars and crumple zones 'give way'
in an impact so increasing the impact time
- We can use the conservation of momentum
to find the speed of a car before impact
- Current electricity
- 4.1 Electrical charges
- Certain insulating materials become
charged when rubbed together
- Electrons are transferred
when objects become charged
- Like charges repel,
unlike charges
atract
- Keywords: Insulating, electron, attract, repel
- 4.2 Electric circuits
- Every component has
its own agreed symbol
- I = Q / t
- 4.3 Resistance
- V = W / Q = E / Q
- R = V / I
- Ohm's law states that the current through a resistor at constant temperature
is directly proportional to the potential difference across the resistor
- Reversing the current through a component
reversing the potential difference across it
- Keywords: Series, potential difference, parallel,
volt (V), resistance, Ohm's law, ohmic conductor
- 4.4 More current-potential
difference graphs
- In a filament bulb, resistance increases
with increase of the filament temperature
- In a diode the forward resistance
is low and the reverse high
- In a thermistor, resistance
increases as temperature decreases
- In a light-dependent resistor, resistance
decreases as light intensity decreases
- Keywords: Filament bulb, diode,
light-dependent resistor, thermistor
- 4.5 Series circuits
- In a series circuit, the current
is the same in each component
- Adding the potential differences
gives the total potential difference
- Adding the resistances
gives the total resistance
- I = V / R
- 4.6 Parallel circuits
- For components in parallel, the total current
- The bigger the resistance of a
component, the smaller the current is
- In a parallel circuit the potential difference
is the same across each component
- Mains Electricity
- 5.1 Alternating current
- Direct current is in one direction only. Alternating
current repeatedly reverses its current
- The peak voltage of an alternating potential difference
is the maximum voltage measured from 0 volts
- f = 1 / T
- Keywords: Direct current, alternating current,
frequency, live wire, neutral wire, oscilloscope
- 5.2 Cables and plugs
- Sockets and plugs are made of stiff plastic
materials, which enclose the electrical connecions
- Cables consist of 2 or 3 insulated copper wires
surrounded by an outer layer of flexible plastic material
- In a 3 pin plug or cable there is a live (brown),
neutral (blue) and earth wire (green/yellow)
- Keywords: Socket, cable, 3-pin plug
- 5.3 Fuses
- A fuse contains a thin wire that heats up and melts if too
much current passes through it which cuts the current
- A circuit breaker is an electromagnetic switch that opens
and cuts the current off if too much current passes through it
- Keywords: Fuse, circuit breaker, residual current circuit breaker (RCCB)
- 5.4 Electrical power and
potential difference
- The power supplied to a device is the energy transferred to it each second
- P = I x V
- The correct rating for a
fuse is power (watts) / volts
- 5.5 Electrical energy and charge
- An electrical current is
the rate of flow of charge
- Q = I x t
- When charge flows through a resistor,
energy transferred to a resistor makes it hot
- E = V x Q
- 5.6 Electrical issues
- Electrical faults are dangerous because
they can cause electric shocks and fires
- Never touch a mains appliance with wet hands. Never touch a
bare wire or terminal at a potential difference of more than ≥ 30 v
- Check cables, plugs and
sockets for damage regularly
- Radioactivity
- 6.1 Observing nuclear radiation
- A radioactive substance contains unstable
nuclei that become stable by emitting radiation
- There are 3 main types of radiation from radioactive
substances, alpha (α), beta (ß) and gamma (Γ)
- Radioactive decay is a random event and we
cannot influence or predict when it'll happen
- Background radiation is from radioactive
substances in the environment, space or X-rays
- Keywords: Nucleus, proton, neutron,
electron, alpha, beta, gamma (radiation)
- 6.2 The discovery of the nucleus
- Rutherford used the measurements from alpha
particle scattering experiments as evidence that an
atom has a small positively charged central nucleus
where most of the mass of the atom is located
- The nuclear model of the atom correctly explained why the alpha
particles are scattered and why some are scattered through larger angles
- 6.3 Nuclear reactions
- Isotopes of an element are atoms with the
same number of protons but different number
of neutron. Therefore they have the same
atomic numbers but different mass numbers
- Alpha decay is a loss of 2 protons
and neutrons from the nucleus
- Beta decay is when a neutron in the nucleus
changes into a proton and an electron
- Keywords: Ion, isotope, atomic number, mass number
- 6.4 More about
different radiation types
- α radiation is stopped by
paper or a few cm of air
- ß radiation is stopped by thin
metal or roughly 1m of air
- Γ radiation is stopped by thick lead
and has an unlimited range in air
- A magnetic or an electric field can be used to
separate a beam of alpha, beta and gamma radiation
- Alpha, beta and gamma radiation
ionise substances they pass through
- Keyword: Ionisation
- 6.5 Half-life
- The half-life of a radioactive isotope is the average time it takes
for the number of nuclei of the isotope in a sample to halve
- The activity of radioactive source is the
number of nuclei that decay per second
- The number of atoms of a radioactive isotope and
the activity both decrease by half every half-life
- Keyword: Half-life
- 6.6 Radioactivity
at work
- The use we can make of a radioactive isotope depends
on its half-life, and the type of radiation it gives out
- For radioactive dating of a sample, we
need a radioactive isotope that is present
in the sample which has a half-life about
the same as the age of the sample
- Keywords: Tracer, radioactive dating
- Energy from the nucleus
- 7.1 Nuclear fission
- Nuclear fission is the splitting of a nucleus into two
approximately equal fragments and the release of 2 or 3 neutrons
- Nuclear fission occurs when a neutron hits a
uranium-235 or plutonium-239 nucleus which splits it
- A chain reaction occurs when neutrons from
fission go on to cause other fission events
- In a nuclear reactor control rods absorb
fission neutrons to ensure that, on
average, only one neutron per fission
goes on to produce further fission
- Keywords: Nuclear fission, chain reaction
- 7.2 Nuclear fusion
- Nuclear fusion is the process
of forcing two nuclei close
enough together so they
form a single larger nucleus
- Keywords: Nuclear fusion
- Energy is released when two
light nuclei are fused together
- 7.3 Nuclear issues
- Radon gas is an α-emitting isotope that seeps
into houses in certain areas through the ground
- There are thousands of fission reactors
safely in use throughout the world.
None of them are of the same type as
the Chernobyl reactors that exploded
- Nuclear waste is stored in safe and secure conditions for many
years after unused uranium and plutonium is removed from it
- 7.4 The early universe
- A galaxy is a collection of billions of
stars held together by their own gravity
- Before galaxies and stars formed, the
universe was formed of hydrogen and helium
- The force of gravity pulled
matter into galaxies and stars
- Keywords: Gravitational attraction, star
- 7.5 The life history of a star
- Keywords: Protostar, main sequence star, red giant, white dwarf,
black dwarf, supergiant, supernova, neutron star, black hole
- A protostar is a gas and dust cloud
in space that can go on to form a star
- Low mass stars follow the path: protostar,
MS star, red giant, white then black dwarf
- High mass stars follow the path: protostar, MS star, red
supergiant, supernova, black hole (if sufficient mass)
- The sun will eventually become a black dwarf
- A supernova is the explosion of
a supergiant after it collapses
- 7.6 How the chemical
elements formed
- Elements as heavy as iron are formed
inside stars as a result of nuclear fusion
- Elements heavier than iron are formed in
supernovas along with lighter elements
- The sun and the rest of the Solar System
were formed from the debris of a supernova