Physics Additional

Distance-Time graphs

• Gradient = How fast it is travelling
• Flat section = Stopped
• Straight diagonal = Travelling at a constant speed (steeper the line = the faster it is travelling)
• Downhill line = Its going backwards
• Curves = Acceleration/deceleration
• Increase gradeient = Speeding up
• Decrease gradient = Slowing down

Acceleration = How quickly velocity changes

Gravity = A force thaat attracts all masses - only felt with large objects

• Gives things a weight
• Means they accelerate towards earth

• Mass = The amount of 'stuff' in an object (Not a force) (Kg)
• Weight = the pull of gravitational force (Newtons)

Resultant force = The overall force, taking into account all other forces acting upon an object (their direction and force)

• If there is a resultant force then it will cause a change in velocity - no resultant force means no change in speed NOT that it is stopped
• Has to be a resultant force for things to start moving
• If there is a resultant force means there is acceleration

Reaction forces = When two objects interact, the forces they exert are equal or opposite (if you push something, it pushes back just as hard but in the other direction - things only move if one object has less mass than the other

• Friction = Force acting between two surfaces always in the opposite direction to the direction of movement
• Drag in water
• Air resistance in air

1. Thinking distance - Affected by: Speed, Tiredness, Drugs/Alcohol etc.

2. Braking distance - Affected by: Speed, Level of brakes, Level of tyres, Level of grip (road conditions)

When a supply force is moves an object through a distance, energy is transferred and work is done (Joules) 

Gravitational potential energy = Affected by the vertical position of the object and the objects mass

Kinetic energy = Movement energy

• Kinetic energy transferred = work done - e.g. A car stopping, Kinetice energy is converted to heat, sound etc. in brakes
• Kinetic energy gained = potential energy lost

Any object that can go back to its original shape once force is removed has elastic potential - Elastic potential energy is converted into kinetic energy once the force is removed

Power = Can transfer a lot of energy in a short space of time (Watts or J/s)

Car design and Safety

Regenerated brakes = Engine turns backwards to act against kinetic energy

Crumple zones = Increase impact time, more time absorbing impact - slowing kinetic energy (acts as a bumper)

Side impact bars = Help direct kinetic energy away from passengers

Seat belts = Stretch slightly to absorb energy of the wearer

Car power ratings:

The more energy converted from fuel = The faster the car

Fastest speed - When air resistance = Power output so aerodynamics are important

Static electricity

Static build-up = When negatively charged ions are scraped off onto another material due to friction - leaving one material positively charged and the other negatively charged

ONLY -ve ions move

Like charges repel, opposites attract

Current = The flow of electric charge round a circuit - only flow through components with a potential difference (Amps - A) 

Potential difference = Driving force that pushes the current round (Volts - V)

Resistance = slows down the flow of current - directly proportional (ohm - Ω)

Resistor = Current through a resistor is directly proportional

Filament lamp = As the temperature of filament increases so does the resistance

Diode = Current only flows through in one direction - Very high resistance in opposite direction

Resistance increases with temperature

As electrical charge flows through a resistor - heat energy is given off = Causes ions in the resistor to gain kinetic energy and move more, making it harder for charge-carrying electrons to get through --> resistance increases

Limit of current in resistor - More current = Higher temperature --> Increase in resistance --> Current decreases

LDR = As light increases, Resistance falls

Thermistor = As temperature increases, Resistance falls

Series circuits

• One component stops - Whole circuit stops
• Potential difference (voltage) is shared
• Current is the same throughout
• Total resistance = Resistance of all components added up
• Cell voltages add up

Parallel circuits

• Each component is seperately connected - Disconnecting hardly effects other components
• All components get all the voltage
• Current is shared between the branches

Mains electricity

Mains supply = 230V + A.C. (50Hz)

Batteries/Cells = D.C.

Electricity in the home

Plugs + Cables:

3 Wires:

1- Brown live wire - Alternates between high +ve and -ve values

2- Blue nuetral wire (0 Volts)

3- Green + Yellow wire - Works with fuse to prevent fire and electric shocks

Earthing and fuses

If the wire touches the case (metal) which is earthed - causes a large current to flow ---> this surge melts the fuse which breaks the circuit (an earthed conductorm [the metal case] cannot become live)

• Larger current = Thicker cable needed
• Fuse should be rated just higher than normal operating current to be safe

Circuit breakers

Break the circuit by opening switch - they are easily reset but more expensive than fuses

Residual current circuit breakers (RCCB's)

• Detects difference between live and and nuetral wire - cuts of power when there is a difference
• Faster - Doesnt take the time of a fuse melting (safer)
• Works for small surges (which can still be fatal) which wouldnt be enough to melt a fuse

Power and Energy

Resistors always produce heat when current flows through them

Efficiency = The amount of electrical input converted to useful energy

Energy transformed = How much useful energy is created in the circuit

Plum pudding model (theory)= Dense positvely charged atom - negative electrons stuck in it

Rutherford experiment - Fired alpha particles through a thin gold foil

They thought that alpha particles would be deflected by 'plum pudding' however most went straight through, odd one bounced back -----> came to conclusion that:

• Most of the mass is contained in the centre of the atom, positively charged = Nucleus

New Model:

• Nucleus - Protons and Nuetrons tightly packed
• Electrons in shells around the nucleus
• Lots of empty space in the atom

Isotopes
Atoms with the same number of protons but different number of nuetrons - same Atomic number, different Mass number

Most elements have different isotopes but very few are stable - Unstable isotopes tend to be radioactive, decay and give out radiation

Background Radiation
Present at all times:

• Naturally occuring unstable isotopes - Rocks, air, food + building materials
• Radiation from space (cosmic waves) mainly from the sun
• Man-made sources - Nuclear waste + weapons etc.

Alpha = Positive, larger charge, larger mass
Beta = Negative, smaller charge, smaller mass

Both are deflected in magnetic fields - Alpha feels a stronger force but beta is deflected further because it has a much smaller mass (they are deflected in opposite directions)

Radiation harms living cells

Collisions (radiation + living cells) --> ionisation of the cell ----> Either:
Damaging or destroying cells  OR  Minor damage --> Mutant cells --> Divide uncontrolably = Cancer

Alpha = Dangerous inside the body because it is larger and cannot escape but is also more ionising
Beta and Gamma = More dangerous oytside the body because they can pass through the skin, whereas alpha cannot

Extent of harmful effects depends on:

• How much exposure
• Energy and penetration of radiation (what type)

 Lead absorbs all 3 types of radiation

Half-life

As more nuclear particles (nuclei) are given out, radiation decreases but never reaches zero radiation

Half-life = Average time it takes for number of nuclei in radioactive material to halve

Uses of radiation:

• Smoke detectors - Alpha (α) radiation causes ionisation and a current flows between two electrodes. Smoke absorbs radiation --> Current stops --> Alarm sounds
• Medical tracers - Short half-life - Beta (β) or Gamma (γ) emitters (so it doesnt harm patient) radiation can be tracked by external detectors
  
• Radio therapy - Cancer treatment - Gamma (γ) kells cells with cancer but often damages other cells making patient ill
• Sterilisation of food/surgical instruments - High dose of gamma (γ) kills microbes without damaging food or instrument unlike sterilisation through boiling  -   Emitter needs long half-life so it can be used for many instruments/food in one go before replacement

Life cycle of a star

Protostar- stars form as clouds of dust and gas collapse under gravitational force, gravitational force rises, increasing the temperature until hydrogen nuclei undergo nuclear fusion to form helium nuclei, giving out heat and light

Main Sequence Star- long stable period, forces balance as it burns. smaller stars burn much faster because large stars burn the hydrogen faster

Stars smaller than the sun form a Red Giant- Hydrogen runs out and heavier elements are formed from nuclear fusion cause the star to swell. It then begins to become more dense when gravity forces the star to compress and creates a White dwarf

Life cycle of a star - continued

Stars larger than the sun form a Red Super Giant- Which undergoes more nuclear fusion and the star expands and contracts due to the unbalancing forces

Eventually they explode and form Supernova- forming heavier elements and ejecting them to form new planets and stars

The supernova loses its outer layers and bcomes much smaller and more dense, leaving a Nuetron star- where the electrons have been forced into the nucleus by gravity, it gives out X-rays and gamma rays

If the star is big enough it will become a Black hole- in which gravity can be strong enough to pull in light

Nuclear

Fission = Splitting up a big atom

• Nuclear power stations use it (gives out lots of energy)
• Problems = Radiation catastrophes + Disposing of the waste

Fusion = Joining of small atomic nuclei

• More radiation for size compared to fission
• Limited waste
• Problem = Needs incredibly high temperatures and pressure, which cannot be created in any container
• Stars use fusion - but hasnt been recreated on earth yet