Physics Unit 2 Aqa

Steady speed

Stopped

Accelerate

Decelerate

Steady Speed

Speed (M/S)

Acceleration

Steady speed

Increasing acceleration

Deceleration

The area under graph

Acceleration (M/s^2) = Change in velocity/Time

Weight = mass(kg)*gravitational field strength(g)

It's caused by gravity so it changes if gravity is different.

The overall effect of forces acting along the same line.

If there is a resultant force the object will change its state of rest/motion, so it will change the velocity.

If the resultant force on a stationary object is 0 it remains stationary, if it's moving it remains at the same velocity. If there is a non zero resultant force it will accelerate.

Resultant force (N) = Mass (kg) * Acceleration (M/S^2)

They exert equal and opposite forces, the one with the smaller mass will accelerate more.

Acts in opposite direction to movement, for a steady speed, friction = driving force. Occurs between 2 surfaces or through a fluid (drag)

Frictional forces in fluids increase with speed.

Make the object streamlined

As speed increases so does gravity, so the object reaches a steady speed. Making a bigger surface area will decrease terminal velocity.

Sum of thinking distance + braking distance.

Speed, dopeyness

Speed, good brakes, good tyres, good grip (surface, weather, tyre)

When a force moves an object through a distance, energy is transferred and work is done.

Work done (j) = force (n) * distance (m)

Energy given because of vertical position in a gravitational field.

GPE (j) = mass (kg) * g * height (m)

KE (j) = 1/2 * mass (kg) * speed^2 (m/s)

To stop a car kinetic energy is converted to heat energy as friction.

Kinetic energy = Work done

Falling objects will convert potential energy to kinetic energy, some of this is converted to heat and sound.

Space shuttles have heat shields which lose heat quickly.

Work done to change the objects shape is stored then converted to kinetic energy when the force is removed.

Force (n) = Spring constant (k) * extension

The maximum force the object can take + still extend proportionality.

Power (W or J/s) = (Work done/energy transformed(j))/(Time (s))

Time run upstairs, Power = (mass*g*height)/time

Time acceleration, Power = (1/2*mass*velocity^2)/time

Momentum (kgm/s) = Mass(kg)*velocity(m/s)

The total momentum before an event is the same as after the event

Before total = momentum a + momentum b

After total = (both masses) * total velocity

Before total = no momentum

After total = momentum a + momentum b

It will get a faster change of momentum.

Reduce kinetic energy by transferring it to heat + sound

Regenerative brakes - Put the motor in reverse and converts kinetic energy into electrical energy, that's stored as chemical energy in the battery.

By converting kinetic energy in a safe way.

Crumple zone - Front + back of car, energy converted as it changes shape.

Side impact bars - Strong metal tubes, directs energy to places like the crumple zone.

Seat belts - Absorbs energy + increases time for user to stop.

Air bags - Slow you down, stop hitting hard surface.

More powerful engine = faster top speed

Aerodynamic cars are faster, more powerful

Electrons move from one object to another creating a negative and positive charge. Opposite charges attract and same charges repel.

Flow of electric charge around a circuit.

Work done to push the current around

Things which slow down the current.

Current (A) = Charge (C) / Time (s)

PD (V) = Work done (j)/ Charge (c)

Use to find out the resistance of a component.

Used to get resistance graphs.

Voltmeter must be in parallel.

Variable resistor allows you to get many readings.

Resistors - Straight line

Filament lamp - S shape, as temperature increases so does the resistance.

Diode - Reverse curved L, but only in the first quadrant, current only flows in one direction.

When charge flows through a resistor heat energy causes ions to vibrate more, making it harder for charge to pass through the resistor.

PD (V) = Current (I) * Resistance (R)

Diode - semiconductor, regulates voltage, and current flows in one direction.

LED - emits light when current goes in a forward direction. Used more as lighting as they have a smaller current (digital clocks, traffic lights, remote controls)

LDR - resistance decreases as light intensity increases.

Thermistor - Resistance decreases as temperature increases

Everything must be connected.

Potential difference is shared out (More cells = more voltage)

Current is the same

Resistance adds up to make the total resistance.

You can remove components

Potential difference is the same everywhere

Current is shared between branches.

AC, 230 volts, 50Hz frequency.

Shows a trace, vertical height with AC is input voltage.

With DC distance from the straight line trace is voltage.

Frequency (Hz) = 1/time period (s)

Long/frayed cables or in contact with something hot/wet. Water near sockets, shoving into sockets, damaged plugs, too many plugs in a socket, lighting sockets with no bulbs, appliances without covers.

Copper core + plastic coating.

Live wire (AC), Neutral wire (0v).

The earth wire protects wiring and works with the fuse to prevent shocks. It's attatched to the metal casing and carries the electricity to the earth.

Each wire is connected to a pin and screwed in. A cable grip is fastened over the cable outer layer. Thicker cables have less resistance (carry more current)

Metal parts are copper/brass = conductors.

Case, cable grip, cable insulators are rubber/plastic = insulators and flexible.

Has a plastic casing and no metal parts showing. Doesn't need and earth wire so it's a two core cable.

Fault in live wire (touches metal case) because case is earthed too much current goes through the earth wire which melts the fuse/trips the circuit breaker if the surge is greater than the fuse rating - breaks the circuit.

Stops fire and electric shocks and stops the rest of the circuit from frying.

Fuses are rated slightly higher than normal current

Break the circuit by opening a switch, you don't have to replace them but they're more expensive than fuses.

Residual circuit breaker - Touch a live wire, less current goes through the neutral wire, difference is detected by the breaker and it opens a switch. They work faster an only need small current changes.

Motors, light bulbs, hair dryers, and speakers.

Filamnet bulbs work by passing a current through a thin wire so it glows.

CFB + LED are much more efficient but they cost more.

(kj) = Power (kw) * time (s)

(kw) = Current (a) * potential difference (v)

(j) = Charge (c) * Potential difference (v)

When a charge goes through a voltage charge energy is transferred, it is supplied at the power source to raise it through a potential.

Charge gives up the energy when it falls through a potential drop.

Battery with more voltage supplies more energy (charge is higher at the start)

Democritus said matter was tiny spheres.

JJThomson discovered electrons could be removed so they must be positive spheres with electrons stuck in.

Fired alpha particles at gold foil (would be slightly deflected), they went straight through one came straight back. Mass was just a tiny positive nucleus.

Proton - 1, +1

Neutron - 1, 0

Electron - 1/2000, -1

Same number of protons (same atomic number)

Different number of neutrons (different mass number)

Radioactive isotopes are unstable and decay into other elements

Random, unaffected by physical conditions (temp, chemical bonding)

Unstable isotopes (air, food, rocks), cosmic rays, nuclear things

Some rocks cause higher levels at the surface

High altitudes (more cosmic rays)

Underground (more rocks)

Nuclear industry workers are exposed to a lot more

Radiographers wear lead aprons and stand behind lead screens

Ap - 2 neutrons + 2 protons, big, heavy, slow moving (Strongly ionising). Don't penetrate far into materials, stopped quickly even in air.

BP - 1 electron, fast, small (moderately ionising)

Penetrate moderately, have a long range in air

GR - Penetrate far into materials, pass straight through air (weakly ionising)

Alpha decay - Atomic mass -4, Atomic number -2

Beta decay - Atomic mass (same), Atomic number +1

Alpha + beta are deflected in opposite directions because of their opposite charges.

Alpha has a large charge and feels a greater force but is large so deflects less.

Average time it takes for the number of nuclei in a radioactive isotope sample to halve. (The count rate falls to half its initial level)

Smoke detector - alpha creates a current between electrodes, smoke absorbs radiation, current stops + alarm sounds.

Tracers - gamma/beta emitters are injected into the body + followed with external detector, radioactivity disappears quickly.

Radiotherapy - Gamma rays kill cancer cells

Sterilisation - Gamma rays kill microbes, sterilise medical instruments and fresh food.

Collisions cause ionisation, low doses will cause cancer but high doses can cause radiation sickness.

Outside body - (Beta + gamma dangerous) - get into organs

Inside body - (Alpha dangerous) - damage in localised area

Short time as possible

Use tongs

Hold at arms length

Keep away from body, avoid looking at

Store in lead box, lead aprons, lead screens

2 light nuclei join, releases a lot of energy (occurs in stars)

It doesn't leave much waste, and we have lots of hydrogen, but needs a really high temperature

To hold the hydrogen you need a strong magnetic field

Split up atomic nuclei, used in nuclear power stations since it releases heat energy, uranium-235 or plutonium-239

A neutron is absorbed into the nucleus, makes it unstable so it splits. This spits out more neutrons so a chain reaction occurs.

It releases a lot of energy but the products are radioactive so are waste. The fuel is cheap but it's expensive because of setting up and decommissioning the power plant, there's the risk of radiation leaks.

Protostar, main sequence star, giant

Red giant -> white dwarf -> black dwarf

Red super giant -> supernova -> black hole or neutron star

P - Formed from clouds of dust + gas. Gravitational energy goes to heat energy increase temperature. Once high enough fusion occurs so heat + light are given out.

MSS - Heat created provides an outward pressure to balance the force of gravity this stable period lasts billions of years

Hydrogen runs out so heavier elements are made so it swells and surface cools.

RG - Will become unstable + eject outer layer as a planetary nebula. Then goes to white dwarf as a hot dense solid core which becomes a black dwarf.

RSG - It begins to glow again, undergoes more fusion and explodes in a supernova, leaving a neutron star or black hole