P8 Flashcards
What is the average walking speed?
~1.4 m/s (5 km/h)
What is the speed of sound in air?
340 m/s
What’s the average human reaction time?
~0.25 seconds (250 milliseconds)
What’s the formula for acceleration?
a = F/m
How do you convert from km/h to m/s?
Divide by 3.6 (or convert step-by-step: km → m, hours → seconds
What are the two components of stopping distance?
• Thinking distance: distance travelled during reaction time
• Braking distance: distance while slowing to a stop
What factors affect thinking distance?
• Speed
• Reaction time
• Distractions
• Tiredness
• Drugs/alcohol
What factors affect braking distance?
• Speed
• Road conditions
• Tyre/brake condition
• Vehicle mass
What happens to stopping distance at higher speeds?
: It increases significantly due to increased kinetic energy.
What danger is caused by hard braking?
Large deceleration → large force → potential injury
How does a seatbelt reduce injury risk?
It stretches, increasing stopping distance and reducing force.
What do crumple zones do?
They absorb energy, increase stopping time, and reduce force.
What is the function of airbags?
Increase time for the head to stop moving → reduce neck force.
How do fossil fuels generate electricity?
Combustion → thermal energy → steam → turbines.
How does nuclear fuel generate electricity?
Fission → thermal energy → steam → turbines.
What is the source of biofuel energy?
Combustion of plant-based material.
How does wind generate electricity?
Turbines rotate directly due to wind.
How does hydroelectricity work?
Falling water (GPE) spins turbines.
What is tidal energy?
Water movement from tides turns turbines in tidal barrages.
How does solar energy work?
Photovoltaic cells directly convert sunlight to electricity.
What energy trend began in the late 1800s?
Rise in coal use during the Industrial Revolution.
What increased in the early 1900s?
Use of petrol and natural gas.
When did nuclear energy become more common?
Since the late 1900s.
When did renewable energy use begin to rise?
Recently, with wind and hydro being most used.
How is electricity transferred in the UK?
Via the National Grid — high-voltage overhead lines.
Why use step-up transformers?
Increase voltage, reduce current, which reduces heat loss.
What is the formula related to power loss?
P = I^2 R
What do step-down transformers do?
Reduce voltage for safe domestic use.
What is the frequency and voltage of mains AC?
50 Hz and 230 V
What is DC?
Direct current — constant voltage (from batteries)
What does the live wire do?
Brown, carries current from mains to appliance.
What does the neutral wire do?
Blue, completes the circuit.
What does the earth wire do?
Green/yellow, connected to casing — safely grounds excess current.
Why is the live wire dangerous even when off?
It can still carry current if circuit is live.
What is red shift?
The increase in wavelength of light from galaxies moving away.
What does red shift support?
Evidence that the universe is expanding.
What is CMBR?
Cosmic Microwave Background Radiation — stretched early-universe radiation.
What does CMBR support?
The Big Bang Theory.
What causes stars to form?
Gravity pulls dust and gas together, increasing temperature and pressure.
What process powers stars?
Nuclear fusion of hydrogen into helium.
What happens when fusion stops?
The star collapses — size determines the outcome.
What does a small/average star become?
White dwarf after a planetary nebula.
What does a massive star become?
Supernova, then a neutron star or black hole.
What affects the radiation emitted by solar bodies?
Their temperature — hotter bodies emit more and shorter wavelengths.
What are the rocky planets?
Mercury, Venus, Earth, Mars.
What are the gas giants?
Jupiter, Saturn, Uranus, Neptune.
Why do larger planets have rings?
Strong gravitational pull traps debris in orbit.
What are moons?
Natural satellites that orbit planets.
What are artificial satellites?
Man-made devices in orbit.
What is a polar orbit used for?
Weather and surveillance — covers the Earth quickly.
What is geostationary orbit used for?
Communications — satellite appears fixed over the equator.
Why do planets orbit in circles?
Due to gravitational force from the Sun.
What happens if a planet moves closer to the Sun?
Orbital speed increases due to increased gravity.
What controls Earth’s temperature?
Balance of EM radiation absorbed vs emitted.
What causes global warming?
More greenhouse gases → more absorption → rising temperature.
What are P-waves?
Longitudinal, fast, travel through solids and liquids.
What are S-waves?
Transverse, slower, only travel through solids.
What do seismic waves tell us about Earth’s core?
S-waves don’t travel through it → liquid outer core.
How is the ocean floor mapped?
Using SONAR — sound waves reflect off the seabed.
What do high-frequency waves detect?
Small features, e.g. fish shoals.
What do low-frequency waves detect?
Deeper sediments — they travel farther due to less energy loss.
What are typical speeds in everyday life?
Walking: 1.4 m/s
• Running: 2.5 m/s
• Cycling: 6 m/s
• Sound in air: 340 m/s
• Wind speed: 5–20 m/s
What is a typical acceleration for a car?
Around 2–3 m/s² (can vary depending on the vehicle).
How do you convert units using ratios?
Use proportional reasoning:
• 1 km = 1000 m
• 1 hour = 3600 s
How can you measure human reaction time?
• Ruler drop test: distance fallen is used to calculate time
• Light or sound response timers
What estimates can you make for large accelerations?
• Emergency stop: up to -6 m/s²
• Rollercoasters or sports cars: 10–15 m/s²
What are the potential differences in live, neutral, and earth wires?
• Live: ~230 V
• Neutral: 0 V
• Earth: 0 V (safety)
Why is a live wire dangerous even when the switch is off?
It can still be at 230 V and cause a shock if touched.
Touching live and earth together can complete a circuit through you
