P8

What factors affect thinking and braking distance

Thinking distance = cruising speed x reaction time
Depends on: Speed, Tiredness, Drugs/Alcohol, phone use (focus)

Braking distance = KE/braking force (½mv²/F)
Depends on: Speed², vehicle mass, quality of brakes

How to calculate Forces in a collision?

Force = change in momentum/time

How to reduce forces in collision

Increase distance it takes to stop
Increase time of collision
Decrease acceleration
Decrease rate of change of momentum

Energy transferred from kinetic store of person to elastic and thermal stores of safety features
Done through features eg. air bags, seatbelts, crumple zones

Difference between non-renewable and renewable energy sources

Non-renewable sources are used faster than they can be replaced but renewable sources are constantly being replenished

Examples of renewable and non-renewable energy sources?

Renewable: Solar, wind, biofuels, tidal, geothermal, hydroelectric power

Non-renewable: Coal, nuclear, oil and natural gas power stations

General pros and cons of different energy sources?

Comment on:
-Renewable?
-Releases CO₂?
-Cost to run?
-Cost to build?
-Special considerations

How is electricity supplied through our homes through the national grid?

At power station, S.U transformer used to step up P.d.
Increased voltage decreases current
Energy loss proportional to current² (P=I²R)
Smaller current reduces energy loss
S.D. Transformer near house produces safer voltage of 230V.
Supplied to home through wires (50Hz.) Must be AC so transformers can be used

How does a UK plug work?

High voltage live wire (brown) carries current into appliance and always attached to fuse
Neutral wire (blue) completes circuit so current can flow
Earth wire (Green+Yellow) a safety device to prevent appliance from becoming live

How does the earth wire act as a safety feature?

If there’s a fault and live wire touches metal case of the appliance, the appliance becomes live
Electric current flows through Earth wire to the ground rather than someone touching it, stopping them from being electrocuted

How does the fuse act as a safety feature?

Fuses have a rating which says how much current flows through it eg. 3A
If too much current flows, heat melts the wire as it’s very thin.
Breaks the circuit stopping anything dangerous

How do isolating transformers work as a safety feature

Same number of turns on both sides
Allows use of electrical device without physically connection to mains
Used in bathrooms and electrical shavers to prevent electrocution

How does double insulation work as a safety feature

If an appliance has an outer case made of something other than metal, it doesn’t need an earth wire and is said to be double insulated
Appliance can’t become live

How do circuit breakers act as a safety feature?

Found in fuse box of many homes
“Trips” and breaks the circuit when it gets too high (current or P.d.)
Can easily be reset
Used to protect appliance or cable from overheating

Some common speeds you should know in m/s

Speed of sound- 340m/s
Speed of light- 299,792,258m/s
Average walking speed- 1.4m/s
Fastest human- 12.4m/s
Wind- 5m/s

What are Earthquakes?

Earth’s crust made up of plates of rock (tectonic plates)
Boundaries between plates called fault lines
Sudden slip of plates sends seismic waves through Earth
Seisometers can be used to detect these waves

What are the 2 diff. seismic waves produced by Earthquakes?

Primary waves- Longitudinal, Faster (5km/s), Can propagate through solids + Liquids

Secondary waves- Transverse, slower (3km/s), Propagate through solids only

How do you map the mantle?

Plot where each type of wave is detected and time-delay in receiving them
Waves travel at varying speeds depending on density of material
Path the waves travel refracted by changes in density
Through this, the structure of Earth can be studied

What are shadow zones?

Zones where one or both types of waves aren’t detected
Existence of secondary wave shadow zones shows earth has liquid outer core
Existence of partial primary wave shadow zones shows Earth has solid inner core

What are black-bodies?

A black body object emits and absorbs every wavelength of EM radiation eg. stars

How do scientists determine which colour a star is?

Plot intensity of received radiation for each wavelength
Peak intensity determined by temperature of object
Hotter object, shorter peak wavelength
Total amount of energy emitted also increases with temp.

Which colour stars are the hottest?

Blue stars are hotter
Medium stars emit peak wavelength in green part of spectrum but give enough red and blue to look white
Cooler stars primarily give off yellow and red light

How is radiation dealt with in the atmosphere?

Short wavelength visible light pass through atmosphere mainly unobstructed, some reflects from clouds
Earth absorbs radiation and heads up. Warm enough to emit only long wavelength infrared radiation
IR absorbed by greenhouse gases in atmosphere, heating it
IR radiation absorbed by atmosphere and re-emitted in all directions, some back to surface of Earth

What is the order in our solar system

Anything that orbits around the sun (planets, dwarves moons etc.)

Mercury → Venus → Earth → Mars → Asteroid belt → Saturn → Uranus → Neptune → Pluto → Makemake → Kuiper belt

How does gravity hold the solar system together

All objects in solar system attracted together due to gravity
Sun most massive object therefore largest force of gravity
Larger objects’ masses and closer together, greater force of gravity

How do orbits work?

Centripetal force is gravitational force for celestial objects in orbit around another object
Force gravity gets weaker with distance according to inverse square law (F_g = 1/d²)
Larger force on object, faster orbit so objects closest to sun orbit fastest

Rules of circular motion

Any kind of circular motion a centripetal force always needs:
Force acting towards centre of orbit
Force/acceleration at right angles to direction of movement (velocity)
Velocity changing as direction changing but speed constant

Describe how gravity, speed of comet and direction of its tail changes as it orbits the sun

Gravity- comet highly elliptical so distance between comet and sun greatly varies so gravitational force changes a lot (according to inverse square law)

Speed- when gravity is weaker at further distances, comet travels slower and vice versa

Tail- Always points away from sun as sunlight hits it, only visible close to the sun as sunlight hot enough to sublimate ice on comet

What is a geostationary orbit satellite?

Orbits Earth once in 24 hours
Remains in fixed position above Earth’s surface
Orbits Earth above equator
Used for communication satellites

What are low polar orbit satellites

Have very short period
Travels pole to pole
Can observe every part of Earth over time
Relatively close to Earth’s surface
Used as weather, mapping and spy satellites

How are stars formed

Formed from gas clouds (nebulae) that collapse due to gravitational force, produces protostar
When protostar large and hot enough, fuses hydrogen to helium in core
Now called a main sequence star

What is the life cycle of a low-medium sized star?

Once nuclear fusion stops, expands and cool to become red giants
Lose outer gas layers to form planetary nebula
Centre of star collapses to form small and hot white dwarf
White dwarf cools over to form brown dwarf and eventually a black dwarf

What is the life cycle of larger stars

Once nuclear fusion stops, expands and cool to become red supergiants
Centre of star continues to collapse until it explodes in a supernova
Remaining star collapses to form neutron star or black hole
Black holes have such large mass and gravity that even light can’t escape

What is the doppler effect?

Apparent change in frequency of wave due to movement of source of wave
If object emitting waves moving away from observer, wavelength increases so frequency decrease (vice versa)

Difference between a red shift and blue shift in space?

Red shift- galaxy receding, light waves stretched

Blue shift- galaxy approaching, light waves compressed

How are shifts visualised?

See shifts using absorption spectra emitted by stars (from P7) eg. if everything moves towards red light then red shift
Atmospheric hydrogen absorbs particular colours of light (as contains right amount of energy for electrons to excite)

What were Hubble’s observations?

Found all galaxies red shift and moving away, universe expanding
Used red shift to calculate velocities of galaxies against distance from Earth
Distant galaxies had bigger red shifts as moving away faster

What other evidence is there for Big Bang?

Cosmic microwave background radiation (CMBR): 1960s- scientists discovered microwave radiation from all directions of Universe
Radiation believed to be heat radiation left over from Big Bang
Radiation had high frequency but stretched over time so became microwaves