Physics 2

Distance

Distance-Time Graphs• Gradient = Speed• Flat sections are stationary• Straight = steady speed• Curves= acceleration or

deceleration

Velocity and Acceleration

Acceleration is how quickly velocity is changingAcceleration=Change in Velocity/Time Taken

Velocity-Time Graphs• Gradient = Acceleration• Flat sections = steady speed• Area under the graph

represents distance • Curve is change in

acceleration

Weight

• MASS is the “stuff” inside, whereas WEIGHT is the force due to gravity

• Weight = Mass x Gravitational Field Strength• Earths GFS is 10N/Kg

Resultant Forces

• It is the overall FORCE• The overall effect of forces which will decide

the motion of an object• If two forces are acting in the same direction,

the resultant force is the sum of those two• If two forces are acting along the same line,

then the resultant force is found by subtracting them

Driving force =1000N

Pushing Force =600N

Resultant Force =1600N

Driving force =1000NFriction

=600N

Resultant Force =400N

Acceleration

• If the resultant force in 0 the object is stationary • It there is no resultant force on a moving object,

then it will carry on moving with constant velocity

• If there is an resultant force, then the object will accelerate in the direction of the force

• That is until the force equal out again

• Force = Mass x Acceleration Or Acceleration = Force / Mass

• When two object interact, the forces they put (exert) upon each other are equal and opposite

• This is called a reaction force, so if you push against something it will push back against you with equal force

Friction

• It acts against movement• If you travel at a steady speed, the driving

force needs to equal the frictional force• Streamlining reduces drag or air resistance• Drag increases as speed increases, as you

accelerate you hit more air particles with more force. This created more drag

Terminal Velocity

• When an object first falls, gravity (weight) has more force than frictional forces

• This causes the object to accelerate downwards

• As the speed increases, so does the drag• This reduces the acceleration• Weight can not get any bigger,

so you reach terminal velocity (fall at a steady speed)

Stopping Distance

Thinking Distance• Faster you are going = Further you will go• Your Reactions- Tiredness, drugs, alcohol, bad

visibility and distractions Braking Distance• Faster you are going = Further you will go• The Car- the condition of Tyres and condition of

Brakes• The Road- road surface and weather condition

30 mph

50 mph

70 mph

9m

15m

21m

14m

38m

75m

So this shows that thinking distance is directionally proportional but braking distance is squarely proportional

Thinking Braking Distance Distance

Stopping Dis. = Thinking Dis. + Braking Dis.

Work Done

• To move an object energy has to be transferred

• The energy can be used usefully i.e. To move something or wastefully i.e. Friction

• Work Done= Force x Distance Moved

Gravitational Potential Energy

• When an object is lifted vertically work is done against the force of gravity. This is transferred into gravitational potential energy (GPE)

• GPE= Mass x Height x GFS (gravitational field strength)

• The Earth has a GFS of 10N/Kg

Kinetic Energy

• Any thing that moves has kinetic energy• Kinetic Energy = ½ Mass x Speed²• Moving car has lots of KE so to slow it down

energy is lost i.e. Heat energy • Work done = KE F x d = ½ mv²• Falling objects have the potential energy lost and

they gain kinetic energy

Elasticity

• Apply a force = Stretch the Object• Work done is stored as ELASTIC POTENTIAL

ENERGY• Then its goes back to its original shape

releasing the energy as KINETIC ENERGY

• Extension of Spring is DIRECTIONALLY PROPORTIONAL to the force applied

• Force = K (spring constant) x energy• There is a limit to a springs elasticity, it is

normal until it reaches its maximum force• Past this point the spring will not

return to its original shape

Power

• It is the rate of doing work

• Power = Work Done / Time Taken

• Measured in Watts, which means 1 Watt is 1 joule of energy transferred every second

Momentum

• It’s a property of a moving object• Momentum = Mass x Velocity• Also P before = P after• Momentum is a vector, so has direction• When a force acts upon an object it changes

its momentum• The bigger the force the faster the change of

momentum

Car Safety

• Brakes transform the kinetic energy of the car into thermal energy on the road

• Regenerative brakes don’t transform into heat the transform into electrical energy

• Big change in Momentum in a short time = MASSIVE

END OF FIRST HALF

Static Electricity

• It is created when two object rub against each other and either lose or gain electrons

• Like charges repel, so if hair had been charged then the hair would separate because their like charges repel each other

• However these charges can be easily lost through a conductor

Current and Voltage

• Current is the rate of flow of charge• Current= Charge / Time• The Potential Difference is the work done per

coulomb of charge • Voltage = Work Done / Charge

Circuits

Resistance

Current through a resistor (at constant temp.) is directionally proportional to Voltage

The higher the resistance the higher the potential difference

However in a normal filament lamp the temperature of the filament increases this causes the curve

This is a Diode. The current will only flow in one direction. The diode has a very high resistance in the opposite direction

Series

• All or nothing, if one component breaks ao does the circuit

• Potential difference is shared out, so in 23 fairy-lights on the mains electricity they all have a voltage of 10V

• Current is the same everywhere• And the Resistance builds/adds up, 5 bulbs

with 10Ω so the circuit has 50Ω

Parallel

• Things can be switched off separately• Voltage is the same across all components• However current is shared between each

branch. The current going in is the same as going out, but the components have different currents going across them

Mains Electricity

• Supplied in AC• Has 230V• And has frequency of 50Hz• It can be shown on an oscilloscope

Electricity in the Home

Hazards: Long Cables; Frayed cables; damaged plugs; too many plugs in 1 socket; water near sockets

The wires: Live wire carries the alternating current; Neutral has 0V and Earth is attached to metal casing

BLUE E F T

BROWN I G H T

Fuses and Earthing

• Fault in the LIVE WIRE causes it to touch the metal case

• This causes a larger current to flow through the circuit

• This surge cause the FUSE to MELT• This cuts of the live supply and breaks the

circuit, THUS saving the appliance and the user

Live wire touches the metal casing

Big Surge of Electricity to earth

Fault in the Live Wire

The Fuse melts/blows The appliance is SAFE

Energy and Power

• All resistors produce heat when a current flows through them. The more current the more heat

• To be energy efficient they have to transfer more of their total electrical energy to a useful source

• Energy Transferred= Power Rating x Time

Atomic Structure- Rutherford

• In 1909 Rutherford fired alpha particles at gold foil to discover more about particles

• He found most went straight through, this shows particles are mostly empty space

• Some came straight back, the shows that most of the mass is concentration in a central nucleus

• Some were deflected, this shows the nucleus is positive and there must be negative electrons not in the nucleus

Radiation

• Isotopes are atoms of the same element but are slightly different, they have the same number of protons but different numbers of neutrons

• Radioactivity is entirely random, it comes from an unstable and decaying nuclei. This emits alpha, beta or gamma radiation

• Background radiation comes from: naturally unstable isotopes like rocks and food; space like cosmic rays; Man-made places like weapons and medicine and power-stations

Types of Radiation

Alpha radiation is a helium nucleus, so two protons and two neutrons. Can’t penetrate much but because of its size it’s strongly ionising (bash into atoms and knock electrons off of them)

Beta radiation is an electron which is emitted when a neutron turns into a proton. Can go through some things and is mildly ionising

Gamma radiation is an ray. This penetrates everything but is weakly ionising.

Radiation Safety

• Radiation damage depend on the type of radiation and how long you were exposed

• Alpha particles are deflected slightly by magnetic field but beta particles are extremely deflected by the magnetic field

• Granite release radon gas which can be trapped in peoples houses

• Nuclear industry workers wear protective clothing and face masks and have radiation badges

• Radiographers work behind lead screens and wear lead aprons

Half-Life

• Half life is the AVERAGE TIME it takes for the NUMBER OF NUCLEI in a radioactive isotope to HALVE

• Radioactivity never stops, there will always be some activity, so its hard to measure

• Short half life means lots of nuclei decay quickly, activity falls quickly

-1 Half Life- -1 Half Life- -1 Half Life-

Uses of Radiation

• Smoke detectors- alpha particles make and circuit and smoke breaks the circuit, making the alarm go off

• Sterilisation- Gamma rays are used to kill bacteria on food or medical equipment, without harming them

• Radiotherapy- gamma is fired at a cancer to kill all of those cells, but damage is done

• Tracers- beta or gamma sources are put into someone and an external detector says where most of the radiation is

Damage of Radioactivity

• Large amounts of radiation kill cells and leave you with radiation sickness, but nothing else

• Small amounts cause minor damage to cells without killing them. They then mutant and divide uncontrollably, this is a cancer

• Alpha is very harmful inside the body because it damages a very localised area

• Beta and gamma are dangerous outside the body because they can penetrate the skin

Nuclear Fission

• This is what happens in nuclear power stations and nuclear bombs

• An Neutron had to be absorbed by an unstable nuclei

• This creates two new smaller nuclei and releases more neutron, this makes a chain reaction

• This gives out a lot of energy

Nuclear Fusion

• This is where two small nuclei join to create a larger nucleus and energy

• Fusion doesn’t leave a lot of radioactive waste and there is a bounty of fuel (hydrogen)

• It can only happen at really high temperatures• You need at strong magnetic force to hold the

pressure and heat

2

1 H H1

1+ 3

2He + ENERGY

Life Cycle of Stars

Nebula- The nursery for Stars. Clouds of Dust and gas start to form. Gravity makes it spiral and form a Protostar

Protostar- Gravity is turned into heat. The temp is then high enough for nucleur fusion to start. This gives out light, star

Main Sequence star- long stable period where outward pressure is equal to the force of gravity (the sun) but this can’t last forever

Red Giant- hydrogen has run out and it was a small star

Red SuperGiant- Hydrogen has run out but it was a big star

OR

Red Giant

Red Giant- small star make this. It is unstable so ejects its outer layer of dust and gas.

White Dwarf- This is what’s left after the red giant. It is a hot solid, dense core. When it cools down it becomes a Black Dwarf

Planetary Nebula- This is the outer layer of duct and gas.

Red SuperGiant

Red SuperGiant- This is made from large stars. They glow more brightly because they do more fusion, so they expand

Supernova- This is the explosion of the Red SuperGiant. It forms elements heavier than iron and spreads them out into the universe creating new planets and new stars

Neutron Star- What is left of the supernova is a dense core. This is an neutron star

OR

Black Hole- If the star is big enough the remains of the supernova will form a black hole