physics - topic 8: global challenges

What are the estimated speeds for walking, running, cycling, and driving on motorways and quiet roads?

Walking- 3mph

Running- 6.7mph

Cycling- 12.3mph

Driving (motorway)- 70mph

Driving (quieter roads)- 30mph

What is the difference between thinking and braking distance?

Thinking- The distance the vehicle travels in your reaction time

Stopping- The distance it takes for you to come to a stop

What factors can affect braking distance?

• Speed

• Ice

• Brake/tire conditions

• Mass of the car (passengers)

What factors can affect thinking distance?

• Fatigue or illness

• Drugs

• Alcohol

• Distractions e.g. phone

What parts of a car can reduce forces in a collision?

• Crumple Zone - deforms on impacts and absorbs KE

• Airbags - cushioning

• Anti Lock Braking Systems - brakes switch on and off so they don’t lock

• Seatbelts

What experiment can test reaction time?

Ruler Drop Experiment

What happens in a nuclear power station?

• Nuclear fuel (e.g. uranium) undergoes nuclear fission

• The energy released heats water into steam

• The steam turns the turbine

• The turbine drives a generator, which produces electricity

• Advantages: reliable, no CO₂ during generation, high energy output

• Disadvantages: radioactive waste, expensive

What happens in a fossil fuel power station?

• Fossil fuels are burned

• The heat boils water to form water

• Steam turns a turbine

• The turbine drives a generator which produces electricity.

• Advantages: reliable, high power output.

• Disadvantages: non-renewable, releases CO₂ and pollutants.

Examples of renewable energy:

• Solar

• Wind

• Tidal

• Geothermal (hot energy under the earth)

• Biofuel/biomass

Examples of non-renewable energy:

• Fossil fuels (coal, oil, natural gas)

• Nuclear energy (uranium)

What is the voltage and hertz of a UK plug?

230V, 50Hz

What is the National Grid?

A system consisting of cables and transformers that link power houses to consumers (houses or factories).

Do step-up transformers increase or decrease current? Why?

Decrease - Minimses power loss

Do step-down transformers increase or decrease voltage? Why?

Decrease - Provides safe and usable power to homes

What are the three wires in a UK plug?

Brown Live Wire- Carries current at a high voltage into the appliance

Blue Neutral Wire- Makes the circuit complete so current can flow

Earth Wire- A safety device to prevent the appliance becoming live

Where are the wires located in the plug?

Brown - Right (connected to fuse)

Blue - Left

Green/yellow earth - Top

All wires are connected to a cable grip, which connects to the outer insulation.

What are the two safety features on a plug?

Earth Wire:

• Thick with low resistance

• If there is a fault, the current travels through this wire to the ground

Fuse:

• A hollow tube with wire running down the middle

• If too much current flows, it melts the fuse and the circuit will break

How do you determine which fuse to get?

Divide the power rating (Watts) by the mains voltage (230V) to get the current. Round this number up.

What are the electricity safety features found in a house? Where is it found?

Isolating Transformers

• Same turns on both coils

• Allows you to use an electrical device without being connected to the mains

• E.g. found in bathrooms for charging electric brushes

Double Insulation

• Outer plastic casing replaces an earth wire

• Prevents shock when touched

Circuit Breakers

• Found in the fuse box

• The circuit breaker ‘trips’ and breaks when current is too high

  Prevents overheating

What is the outwards structure of the Earth?

Inner iron core (solid), outer core (liquid), mantle (solid), crust (solid)

What are the boundaries between tectonic plates called?

Fault lines

What causes seismic waves?

The sudden slip of the plates

What are the characteristics of P and S waves?

What do the waves look like when travelling through the Earth?

How to remember what P-waves travel through?

P-Waves are superior

• So they travel through liquids AND solids

Why are p and s waves refracted when travelling through the layers of the Earth?

The density is changing

What do we call the area that the waves don’t reach? What does each one prove?

Shadow Zone

S-Wave shadow zone - Proves the Earth has a liquid outer core

P-Wave shadow zone - Proves the Earth has an iron inner core

What is a black body? Example?

A body that emits and absorbs every type of radiation (e.g. stars, black holes)

What is Wien’s Displacement Law?

As an object heats up, its peak wavelength of radiation decreases. It shifts towards the blue-end of the spectrum.

What are the planets in our solar system?

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

What are the two types of satellites and their characteristics?

What is the centripetal force?

The force directed to the centre of orbit

What provides the centripetal force of a celestial object?

The gravitational force between the object and the sun.

What is the relationship between force and distance in orbit?

As distance increases, force decreases (inverse square law)

What sequence do all stars follow up to main sequence?

1. Form in interstellar gas clouds (nebulae)

2. Nebulae collapse due to gravitational force, forming a protostar

3. Nuclear fusion starts - hydrogen fuses into helium

4. Star is stable due to balanced outward (pressure) and inward (gravitational ) forces

What is the life cycle of a low mass star (e.g. our sun) after main sequence?

1. Helium begins to fuse together and the star expands to form a red giant.

2. Its outer layers of gas are ejected to form a planetary nebula.

3. A white dwarf is left behind, which is the hot core.

4. This cools to form a black dwarf.

What is the life cycle of a high mass star after main sequence?

1. Heavier elements begin to fuse, and the star expands to form a red supergiant.

2. Eventually fusion reaches iron, and its outer laters collapse into the star.

3. The core ricochets, creating a supernova.

4. If the remaining core is larger, it becomes a black hole.

5. If not, it becomes a neutron star.

What is the Big Bang?

A theory on the beginning of the universe.

It claims that the universe started at a singular point, which is where all matter and energy was created.

The single point ‘exploded’ and begun to expand.

What is the evidence for the Big Bang?

Red Shifts

• Light from distant galaxies is shifted towards the red end of the spectrum

• The further away a galaxy is, the greater the red-shift

• This shows galaxies are moving away from us

• Therefore, the universe is expanding

Cosmic Microwave Background Radiation

• Scientists Penzias and Wilson discovered that there was microwave radiation coming from all directions

• This is believed to be the VL and IR left from the Big Bang

• The radiation has been stretched over-time, so it now has a wavelength in the microwave region of the EM spectrum

What is the process of the greenhouse effect?

• Short wavelength radiation (UV, VL) heats up the Earth’s surface

• The Earth emits a longer wavelength radiation (IR)

• Radiation is absorbed by greenhouse gases

• Radiation is re-radiated in all directions incl. back to Earth