# Physics

• Created by: victoria
• Created on: 18-04-13 19:22

## Forces and Motion

Forces- objects change motion- change- speed-direction- changes+ acceleration

force=masssxacceleration

(n)      (kg)        (m/s2)                                    M/S"

acceleration= force/mass                                                      ("=2)

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Total stopping distance= thinking distance+braking distance

breaking distance= distance car travels once breaks applies

reaction time= time needed for driver to react

thinking distance= Durning the reaction time the car willl travel a certain distance

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## Forces and Motion 2

Factors that effect thinking distance and reaction time

tierdness                                                     sat nav

drugs                                                           age

alcohol                                                        mobile phones

over the counter drugs                                  talking to passengers

prescription drugs

listening to music

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Faster speed futher car travels durning reaction time

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## Forces and Motion 3

Braking distance

Not only depend on speed of car- worn brakes- reduces force they apply- too much force, wheels lock- car skids.

road conditions- icy- less friction- braking distance increases- worn tyers- wet roads

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Stopping distance

Greater at higher speeds- reason for speed limits ( one of)

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## Work and power

'work done' means= ennergy is being used/ transferred or transformed

work done JOULES

no energy tansfered= no work done

work is allways done when a force is used to move something through a distance againtt an opposing force

Examples of doing work;

climbing stairs

pushing a trolly

pulling a sledge

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## Work and power 2

Amount of work done- depends on force applied- and distance moved in direction of force

work done= force x distance moved in direction of force

(joules, j)     (newtons, N)         ( metres, m)

Distance moved MUST be in same direction as force

Power= The work done in given time OR the rate of doing work WATTS

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## Work and power 3

Vehicle Power

Cars with more powerful engine- travel- accelerate - faster.

Less economical- use fuel quicker

Produce more pollution

Power of vehicle=

Power= Force x Velocity       (p= f x v)

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## Work and power 4

Kinetic Energy

anything moving- kinetic energy

Amount of energy depends mass and velocity

Kinetic energy= 1/2   x  mass x (velocity)2

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Kinetic energy and braking distance

The amount of K.E depends on v2- if velocity doubles- the K>E goes up 4 times. For a car to stop it needs to get rid of this energy and takes up 4 times as much distance to do this

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## Fuels for Vehicles

Petrol/ Diesel

- Both from crude oil, forms of fossil fuels- bad for enviroment- global warming- running out- alternative fuel- increase carbon dioxide- safe for us petrol/diseal- provides us with energy for radio, headlights and engine.

Biofuels

- Burning- carbon dioxide- no overall increase ( plant would have absorbed same amount that is released) Not enough landscape to power all our engines- biodiesel

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Fuel Consumption

Amount of fuel a car uses= fuel consumption   MPG ( MILES PER GALLON)

Fuel consumption varied depending on

Mass of car---- Streamlining----- Driving style ( agressive)----- Accelerating and braking more uses fuel

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## Momentum

Momentum of object depends on mass and velocity

Momentum= mass x velocity

kg m/s          kg          m/s

p=m x v     ( p= momentum)

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## Force and Momentum

Momentum of object changes, there is force on the object that is given by the equation

Force= change in momentum/ time

Car crash- change in momentum- short time= Large forces on occupants

Crumple zones reduce force

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## Collisions and car safety

Paddle control= reduces amount of time diver takes hands off wheel

ABS- Traction Control- Electric Windows- Paddle Controls- Crumple Zones

Seatbelts absorb the energy in a collison

Car saftey features absorb the force so that there is less force is put onto the passengers  BY:

Increasing the time taken for vehicle to stop

Increasing the stoppping distance

Decreasing the acceleration

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## Falling Objects

The mass  of an object is the amount of it in kilograms.

Weight measures the pull of gravity in Newtons

Weight= Mass x G

(n)              (kg)      N/KG

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Drag

Falling objects accellerate becuase of the force of gravity pulling on them- air resistance has an effect.

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## Energy Changes

Falling objects convert gravitational potential energy into kinetic energy

Doubling mass- doubles it K.E

Doubling velocity- increases K.E by a factor of 4

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## The Solar System

8 Main Planets

A number of smaller dwarf planets

My Very Easy Method Just Speeds Up Naming Planets

Mercuary                                     Uranus

Venus                                         Neptune

Earth                                          P= Nothing was Pluto but has been demoted

Mars

Jupiter

Saturn

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## The Solar System 2

All planets including dwarf planets orbit the sun

Suns powerfull gravity keeps them all in orbit

A force that makes an object move in a circular path is called a centripetal force

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Icy comets also orbit the sun travel over a million miles ph

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Black holes-- gravity so strong not even light can escape

Immesirable number of stars

Worm holes

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## The Solar System 3

Our galaxy= Milky way- collection over 200 billion stars

Total- 50 billion galaxys in universe

More stars in the universe than grains of sand in the entire world

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## Exploring Space

Exploring space since 1960s

Probes have been sent to almost every planet- and to most large moons.

Probes- collect data- temperature- magnetic field stregnth- atmosphere- stregnth of gravity

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Stars give out light- we can see them

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## Comets

Large balls of ice and dust

Hundreds orbiting the sun

Unlike most asteroids- highly eliptical ( squahsed circles)

The closer they get to the sun the faster they move ( the suns gravitational attaction is stronger the closer you get to it)

When they get close to the sun- solar wind metls part of the comet and a destinctive trail of debris is formed.

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## Asteroids

Pieces of rock- too small to be classes as planets- unusal shapes- mostly not sphears- gravity not strong enough- Most found inbetween orbits of mars and jupiter, inside asteroid belt.

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## Impact on Earth

Asteroids and comets have hi the earth- will do in future

Impacts from either have thrown large amounts of hot rock and dust into atmosphere

Impacts often explosive- can lead to enormus country wide ( or larger ) fires. Creating more dust- may block at sun.

Devistating effect on life on earth- impact may lead to rapid climate change- resulting in extinction of some species.

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## Impact on Earth

Asteroids and comets have hi the earth- will do in future

Impacts from either have thrown large amounts of hot rock and dust into atmosphere

Impacts often explosive- can lead to enormus country wide ( or larger ) fires. Creating more dust- may block at sun.

Devistating effect on life on earth- impact may lead to rapid climate change- resulting in extinction of some species.

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## The 'Big Bang'

The universe was originally smaller than an atom ( scientists believe)

There was an explosion- the universe has been expanding ever since

Evidence

Red shift- Galaxies that are moving away from us look redder than norma- as the galaxy moves away the wavelegnth of the light it emits gets stretched, making them look redder. More distinct galaxies have larger red shifts showing that they are moving faster

Cosmic Microwave background raditation- Scientists have detected this throughout the atmosphere. Scientists belive it is the heat of the 'big bang'

JUST A THEORY NOT FACTUALLY CORRECT

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## Life cycle of stars

A huge cloud of gass called a nebula ispulled together by gravity forming a protostar

SMALL STARS

Protostar ----> Yellow dwarf ( like our star)-----> Red giant-----> white dwarf -----> black dwarf

LARGE STARS

Protistar---> blue giant-----> red super giant----> super nova-----> black hole

------> neutron star

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## Life cycle of stars ( small stars)

The star is stabe converting hydrogen unto helium + energy = Main sequece star

When the hydrogen is used up the star sweels and cools = Red giant

The Outer layers break away ( a planetary nebula) leaving a small hot core called a white dwarf

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## Life cycle of stars ( large stars)

A large star burns hotter ( a blue giant) and runs out of fuel sooner. It expands and cools = red super giant.

It runs out of fuel- becomes unstable- blows its outer layer in en enormus explosion called SUPERNOVA .

The core of the supernova collapses to a very dense neutron star ( also called a pulsar)

Is this still has a big mass ut continues to collapse under its own gravity, the pull of gravity is so strong that nothing can escape from it not even light= BLACK HOLE

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## Solar Power

Energy from sun- used to generate electricity

Photocells absorb light---> convert into electricity.

Photo pannels absob light---> heat water

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Photocells

When light shines on a photocell- energy absorbed- electrons knocked out of silicon atoms- electrons free to flow- creating direct current.

The amount of electricity produced by a solar cell also depends on the intensity of the light shining on it and how far the solar cell is from the light souce.

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## Solar Power

Solar Ovens

Solar ovens/ solar funaces- used in hot countries.

Like visable rays- infra-red rays reflected by mirrors. Large curved ( concave) mirror- used to collect rays from sun- focus them on kettle or pan for cooking- OR on a thermal tower to make electricity.

Passive Solar Heating

Some buildings- use passive solar heating

Large windows on south side- light energy passes through windows- absorbed by surfaces unside the building- heating them up.

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## Wind Energy

How much energy produced depends on:

height of turbine

angle of vanes

stregnth of wind

number of vanes

shape of vanes

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Winds are Convection currents set up in earths atmosphere by energy from sun. Kinetic energy of wind can be used to drive the wind turbines directly.

ADV---------   Renewable----no waste ---- no poluted gas emited

DISADV----   destroy landscapes---- noisy--- kill birds--- take up room

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## Carbon capture

Carbon dioxide- produced burning fossil fuels-- power stations

collected and stores undeground--- prevent entering atmosphere-- and contributing to global warming.

D.C-= direct current

Always flows around a circuit in the same direction. D.C from batteries

A.C = Alternating currents

Flows backwards and forewards ariund a circuit- constantly changing direction e.g from sockets ( mains).

An oscilloscope can be used to compare and measure currents + voltages.

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## Generating Electricity

If a magnet moves into a coil of wire a current is induced in the coil- If the magnet reverses- so does the current-current only induced when the magnet is moving.

A larger current can be indicated by

More coils

Stronger magnet

Move magnet quicker

Current can also be infuced by spinning a coil of wire between the poles of a magnet

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## Generating Electricity

If a magnet moves into a coil of wire a current is induced in the coil- If the magnet reverses- so does the current-current only induced when the magnet is moving.

A larger current can be indicated by

More coils

Stronger magnet

Move magnet quicker

Current can also be infuced by spinning a coil of wire between the poles of a magnet

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Bicycle Dynamo

A magnet rotates near a coil of wire so that the lines of flux are cut by the wire. The coil is wound on a soft iron core so that the magnetic field is stronger.

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## Generating Electricity 2

Water is heated to produce steam---> steam turns the turbine----> the turbine turns the generator making electricity------> the national grid distributed electricity around the country

Energy changes

Fossil fules ( chemical energy) ---> water/ steam ( heat energy)---> turbines ( kinetic)-------------> Generator ( electricity)

Efficiency

Alot of energy is wasted as heat. The efficency compares how much useful energy us produced to wasted energy.

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## National Grid

This is the system of pylons, cables and transformers that carry electricity around the country. Step-up transformers increase the voltage to about 400,000 V at the power station- this increases the current in the cables making the system more efficient. step-down transformers reduce the voltage to a safer 230 v for our homes. A.C is generated at powerstations becuase transformers fo not work with D.C

Cables above ground becuase

Easier to fix

Futher away

Cheeper, less work

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