Physics 2

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

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

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

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)

• 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

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.

• 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

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

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)

• 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

• 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

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

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

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

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