Physics 2

Helpful Notes created by notes submitted on get revising - all formulas at the back which might be helpful :)

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  • Created by: Summer
  • Created on: 25-05-10 19:07

Representing Motion

Distance Time Graphs

  • The Slope of a Distance Time Graph Represents Speed
  • Speed(m/s) = Distance(m)/Time(s)
  • When an object is stationary the line on the graph is horizontal(flat)
  • When an object is moving at a steady speed the line is straight but sloped.
  • Distance is on the Y axis and Time is on the X axis
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Representing Motion

Velocity Time Graphs

  • The velocity of an object is its speed in a given direction
  • The slope on a velocity time graph represents Acceleration
  • VELOCITY IS SPEED IN A GIVEN DIRECTION
  • ACCELERATION is change of velocity per second
  • Acceleration(m/s/s) = Change in Velocity / Time
  • When an Object is moving with constant velocity the line on the graph is horizontal
  • When an Object is moving with constant acceleration the line is straight but slopped
  • The Gradient of a velocity-time graph represents Acceleration
  • The Area under a velocity time graph represents Distance Travelled
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Newtons three laws of motion

Newtons Three Laws of Motion

  • 1. Every Object in steady motion tends to remain in that state unless an external force applies to it
  • 2.The relationship between an objects mass (m), its acceleration (a), and the applied force (F) can be represented by the equation
  • Resultant Force(N)=mass(kg)xacceleration(m/s2)
  • IF THERE IS AN UNBALANCED FORCE , THEN THE OBJECT WILL ACCELERATE IN THAT DIRECTION
  • 3. for every action there is an equal and opposite reaction
  • if you push against a wall, the wall will push back at you at the same force you applied to it
  • the faster a body moves through a fluid, the greater the frictional force acting on it.
  • a body falling through a fluid will intitailly accelerate due to the force of gravity.
  • EVENTUALLY THE RESULTANT FORCE ON A BODY WILL BE ZERO THEREFORE WILL FALL AT ITS TERMINAL VELOCITY
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Work done

Work-done

  • When a force causes a body to move through a distance, energy is transformed and work is done.
  • WORK DONE(JOULES) = FORCE APPLIED(NEWTONS) X DISTANCE TRAVELLED(METRES)
  • WORK DONE AGAINST FRICTION IS MAINLY TRANSFORMED TO HEAT
  • for an object to recover its original shape, elastic potential is the energy stored in an object when work is done on the object to change its shape
  • the kinetic energy of a body depends on its mass and speed
  • KINETIC ENERGY(Joules) = 1/2 MASS(kg) X VELOCITY squared(m/s/s)
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Momentum and Collisons

  • The faster a body is moving the more kinetic energy is has
  • It also has MOMENTUM
  • When working out what happens to a bodie as a result of a collison/explosion it is more useful to think of it in momentum rarther than energy
  • Momentum,Mass and Velocity Can be related by the equation
  • Momentum(kgm/s) = Mass x Velocity
  • Momentum has both MAGNITUDE AND DIRECTION
  • Momentum is conserved in any Collision/Explosion provided no external forces act upon it
  • When a force acts on an object it causes a change in momentum
  • the larger the force, the faster the change of momentum
  • FORCE ACTING = CHANGE IN MOMENTUM / TIME TAKEN FOR CHANGE
  • Crumple zones crumple on impact. this increses the time taken for the car to stop
  • Seatbelts stretch slighlty . this increses the time taken to stop . it reduces the forces acting upon there chest
  • Airbags alow you to slow down more gradually
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Static Electricty

Static Electricity

  • Some insulating Materials become electrically charged when they are rubbed together
  • Charges that are the same repel, whilst unlike (opposite) charges attract.
  • When certain insulating materials are rubbed against each other they become electrically charged.
  • Negatively charged electrons are rubbed of one material onto the other
  • The material that gains electrons becomes negatively charged
  • The material that loses electrons becomes positivly charged
  • When two electricly charged objects are brought together, they exert a force on each other
  • Electrical Charges can move easily through some substances , e.g metals
  • The rate of flow of electrical charge is called current.
  • A Charged body can be discharged by connecting it to earth with a conductor
  • Charge then flows through the conductor
  • The greater the charge on an isolated body the greater the potentinal differance beetween the body and the earth
  • If the potential differance becomes high enough a spark may jump across the gap beetween the body and any earthered conductor that is brought near it.
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Electrical Circuits

  • Two things are important for a circuit to work: there must be a complete circuit, there must be no short circuits
  • The current that flows through a circuit in series is the same
  • The P.D(Voltage) that flows through a circuit in series is shared
  • The current that flows through a circuit connected in parallel is shared
  • The P.D that flows through a circuit in parallel is the same
  • Current-Potential Difference Graphs are used to show-how the current through a component varies with the P.D across it
  • The Current through a Resistor (at a constant temperature) is directly proportional to the P.D across the resistor
  • P.D = CURRENT X RESISTANCE
  • The resistance of a filament lamp increases as the temperature increases
  • the resistance of a thermister decreses as the temperature increses
  • the resistance of a LDR (Light Dependant Resistor) decreases as light intensity increases
  • The current through a componant depends on its resistance
  • The greater the resistance the smaller the current for a given P.D accross the componant
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Electrical Circuits...

Current-Potential difference graphs are used to show how the current through a component varies with the potential difference across it

  • The current through a resistor(at a constant temperature) is directly proportional to the potential difference across the resistor
  • P.D(Volts) = CURRENT(Amps) X RESISTANCE(Ohms)
  • The resistance of a filament lamp increases as the temperature of the filament lamp increases
  • The current through a diode flows in one direction only, the diode has a high resistance in the reverse direction
  • The resistance of an LDR decreases as light intensity increases
  • The resistance of a Thermister decreases as temperature increases
  • The current through a componant depends on its resistance.
  • The greater the resistance the smaller the current for a given P.D across the compant
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Mains Electricity

Cells and batteries supply current which flows in one direction, this is called direct current or d.c

  • An alternating current is one that is constantly changing direction
  • A Direct current is one that flows in one direction only
  • Mains electricity is a.c supply
  • In the UK, it has a frequency of 50 cycles per second (50 hertz)
  • UK mains supply is 230Volts
  • If an electrical fault causes too great a current the circuit should be switched off by a fuse
  • When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit
  • Appliances with metal cases are usally earthed
  • The earth wire and the fuse together protect the applience and the user
  • The live terminal of the mains supply alternates beetween positive and negative potential with respect to the neutal terminal
  • the neutral terminal stays at a potential close to zerowith respect to the earth
  • Frequency(Hz) = 1/Time Period(peak to peak)
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Electrical Appliances

  • Electrical Appliances Transform energy
  • The power of an electrical appliance is the rate at which is transforms energy
  • Most appliances have their power and the potential difference of the supply printed on them
  • FROM THIS WE CAN CALCULATE THEIR CURRENT AND THE FUSE THEY NEED
  • Electric current is the rate of flow of charge
  • When an electrical charge flows through a resistor, electrical energy is transformed into heat energy
  • The rate at which energy is transformed in a device is called the power
  • Power(Watts) = Energy Transformed(Joules) / Time(Secounds)
  • Power, P.D and current are related by the equation
  • POWER = CURRENT X P.D
  • energy transformed , p.d and charge are related by the equation
  • ENERGY TRANSFORMED(JOULES) = P.D(VOLTS) X CHARGE(COULOMBS)
  • the amount of electrical charge that flows is related to current by the equation
  • CHARGE = CURRENT X TIME
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Atomic Structure (Works of other Scientists)

  • In 1804, John Dalton agreed with Democritus that matter was made up of tiny spheres that could not be broken up
  • Nearly 100 years later, JJ Thompson discovered that electrons can be removed from atoms
  • He suggested that atoms were spheres of positive charge with negatively charged neutrons stuck in them like plums in a plum pudding
  • However in 1909 Rutherford tried firing alpha particles at thin gold foil, most of them went through but some were deflected
  • He then came up with the Nuclear model of the atom
  • The nuclei of some atoms are unstable
  • The can split or decay and release radiation
  • Such isotopes are called Radioactive Isotopes/Radioisotopes
  • When radioactive isotope decays it forms a different atom with a different number of protons
  • When an atom emits alpha/beta radiation its nucleus changes
  • it becomes the nucleus of a different element
  • this is because the number of protons determines what type of atom it is
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Alpha and Beta Decay

Alpha decay

Change in nucleus - Nucleus loses 2 protons and 2 neutrons

Particle Emitted - 2 protons and 2 neutrons emitted as an alpha particle

Beta Decay

Change in nucleus - a neutron in the nucleus changes into a proton

Particle Emitted - an electron is created in the nucleus and instantlly emitted

IN EACH CASE A DIFFERENT ELEMENT IS LEFT BEHIND

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Nuclear Fisson and Fusion

Nuclear Fission - the splitting of atomic nuclei and is used in nuclear reactors as a source of heat energy which can be transformed to eletrical energy

Nuclear Fusion - the joining together of atomic nuclei and is the process by which energy is released in stars

URANIUM- 235 AND PLUTONIUM-239 istopes are normally used as the fuel in nuclear reactors , because their atoms have relativly large nuclei that are easy to split, expecially when hit with neutrons.

ENERGY IS RELEASED IN NUCLEAR REACTOR AS A RESULT OF A PROCESS CALLED NUCLEAR FISSION

THIS EVENT CAN CAUSE OTHER FISSONABLE NUCLEI TO SPLIT, SO PRODUCING A CHAIN REACTION OF EVENTS

The nuclei undergoing fission splits into two smaller nuclei and 2 or 3 neutrons and energy is released

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Nuclear Fussion

THE JOINING TOGETHER OF TWO ATOMIC NUCLEI TO FORM A LARGER ONE

- IT IS THE PROCESS BY WHICH ENERGY IS RELEASED IN STARS

- IT INVOLVES TWO ATOMIC NUCLEI JOINING TOGETHER TO MAKE A LARGE NUCLEUS

- ENERGY IS RELEASED WHEN TIS HAPPENS

- THE SUN AND OTHER STARS USE NUCLEAR FUSION TO RELEASE ENERGY

- THE SEQUENCE OF NUCLEAR FUSION REACTIONS IN A STAR IS COMPLEX, BUT OVERALL HYDROGEN NUCLEI JOIN TO FORM HELIUM NUCLEI

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ALL FORMULA

FORCES AND MOTION

  • Speed(m/s) = Distance(metres)/ Time(seconds)
  • Acceleration(m/s2) = Change in Velocity(m/s)/Time Taken(seconds)
  • Weight(Newtons) = Mass(kg) x Gravitational Field Strength(N/kg)
  • Resultant Force(Newtons) = Mass(kg) x Acceleration(m/s2)
  • Thinking distance + Braking distance = Stopping Distance
  • Work done(Joules) = Force Applied(Newtons) x Distance Moved(Metres)
  • Kinetic Energy(Joules as it is energy) = 1/2 Mass(kg) x Velocity Squared (m/s)
  • Momentum(kgm/s) = Mass(kg) x Velocity(m/s)
  • Force Acting(n) = Change in momentum(kgm/s)/time taken for change to happen

ELECTRICITY

  • RESISTANCE = P.D / CIRRENT
  • Frequency (Hz) = 1/Time Period(s)
  • Energy = Power x Time
  • Power = Voltage x Current
  • Total charge(coulombs) = current x time
  • Energy tranformed = Charge x P.D
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Comments

Rachel

nicely put... simple and to the point, but still including some key details

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