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Velocity & Acceleration Physics Fission and fusion Forces Radioactive decay Work and Energy Power in electrical appliances Momentum Mains Electricity Static Electricity Circuits Unit 2Click on a to jump to that section
Home Next Velocity & AccelerationDistance-time graphs:They show the distance an object,e.g. a car has moved in acertain amount of time.VideosAcceleration Part 1Acceleration Part 2Speed and Velocity
Back Acceleration= change in velocity (m/s) Next (m/s²) Home time taken for change (s)Velocity-time graphs• Velocity is speed in a given direction• Acceleration is change of velocity per secondA body travelling at a steady speed isaccelerating if its direction is changing.
Back NextHome Forces• Force is measured in newtons (N)• The force of friction always acts in the opposite direction of the movement.• Friction occurs when an object moves through air or water, when solid objects slide (they heat up and wear away).• Weight= mass x gravitational field strength(newton, N) (kilogram, kg) (newton/kilogram, N/kg) Usually 10N/Kg, unless the question states otherwise.Stopping DistanceStopping distance of a car= braking + thinking distance Remember: You cannot SLOW down time, you Depends on the weather Depends on the driver’s can just INCREASE conditions (wet/icy roads) reaction time: tiredness, and the vehicle, (worn drugs, alcohol, and the collision time, INCREASE brakes/tyres). speed. reaction time etc.
Back Next Resultant force= mass x acceleration Home (newton, N) (kg) (m/s²) • A stationary object remains still because the resultant force is zero. This is because both forces acting on it are balanced. • E.g. a book is sat on in your hand, the weight of the book is equivalent to the force your hand is exerting to keep it in place.Terminal velocity= constant speedWhen an object falls through a fluid, the faster itmoves, the greater the force of friction.When a body falls:1) At the start, it accelerates (due to the force of gravity-weight),2) Frictional forces (e.g. air resistance) increase …until they balance the gravitational force,3) Then the resultant force is zero, and the body falls at its ‘terminal velocity’.
Back Next Home Work and Energy• A moving object also has movement energy, also called kinetic energy.• When a force moves an object, energy is transferred and work is done: Work done (joules , J) = energy transferred (joules , J)Work done (J) = force applied (N) x distance moved in the direction of the force (m) Kinetic energy= ½ x mass x speed²Kinetic energy can be transformed into other forms of energy as shown in the table:Example: K.Energy is transformed into:A car braking Heat in brakes + An object has more kinetic tyres energy:A wind turbine Electricity, heat, -If it has a bigger mass sound -If it travels at a higher speedRollercoaster car, Gravitationalgoing up a ramp potential energy Video (g.p.e), heat Potential & Kinetic Energy
Back Next Home Momentum • Momentum has both MAGNITUDE and DIRECTION. • ‘Momentum is conserved’ means that the momentum before=momentum after. i.e. the total momentum remains the same. • In a collision, momentum isn’t always conserved because there are external forces acting on the colliding objects.Newtons kgm/s seconds
Back In a car crash… Next• Crumple zones are created to increase collision time, therefore decreasing the force.• Seatbelts stretch slightly, increases the time, decreasing the force acting on the driver.• Airbags also slow you down more gradually.Remember always refer to,‘force= change in momentum ÷ time taken for change’. Home
Back NextHome Static Electricity• Electrostatic precipitators and photocopiers make use of electrostatic charges.• When certain materials rub against each other they become charged.• The material that gains electrons becomes negatively charged.• The material that loses electrons becomes positively charged.
Back NextHome Electrostatic Precipitators Dangers The more charge put on an object, the higher the voltage (p.d) between the object and earth. If the p.d is very high, then a spark can jump between the object and any earthed conductor.• Smoke particles pick up a negative charge.• Smoke particles are attracted to the collecting plates.• Collecting plates are knocked to remove the smoke particles.
Back Next Preventing fires and explosions• A liquid flowing through a pipe can become charged by rubbing. This can be dangerous because it could cause a spark if the substance is inflammable.• Whenever an aeroplane is being refuelled by a tanker, they are always connected by a copper wire.• Friction between the fuel and pipe gains electrons, charging the fuel and pipe, earthing the object prevents a spark and explosion.Home
Back Circuits Next Home ampsResistors in series Resistors in parallel Light Dependent Resistor (LDR) ThermistorThe same current goes through The current is sharedall the components The p.d is equal for bothThe p.d across the cell is sharedResistance= R1 + R2 Voltmeters are placed parallel Ammeters are placed in series
Back NextHome Mains Electricity• Frequency of mains supply in UK = 50 Hertz Alternating Current (a.c) Direct current (d.c) -Is constantly - Flows in only one direction changing direction -As the frequency is 50Hz, each cycle lasts for 1/50th second The mains supply in the UK is 230VThe live terminal alternates between a positive and negative voltage with respect to the neutral terminal. The neutral terminal stays at a voltage close to 0 with respect to earth.
Back Next The 3 pin plug Home The cable has a plastic cover because plastic is a good insulator. Copper wires inside the cable are good conductors.The Earth Wire- for safetyAppliances with metal cases need to be earthed.The case is connected to the earth pin (by the green/yellow wire).If a fault connects the case to the live wire, then a large currentflows to earth and melts the fuse.The fuse:Must be in the live wire so the appliance becomes disconnected,Should have a value (rating) higher than (but as close as possible to) thenormal working current,Can be replaced by a circuit breaker.
Back Next Home Power in electrical appliances• Electrical appliances are used to transform electrical energy to some other useful form of energy.• This may be light, sound, heat, kinetic energy and many more. Power(W)= energy transformed(J) ÷ time taken(s) Power(W)= current (A) x p.d (V) Energy Transferred(J)= p.d (V) x charge (Coulomb) Charge(C)= Current(A) x Time (S)
Back NextHome Radioactive decay• Atomic StructureAt one time, scientists believed in a ‘plum pudding’ model of the atom.They believed that the negative electrons were stuck in a blob ofmatter.Then Rutherford and Marsden fired alpha particles at gold foil (goldleaf) which scattered them, as shown: Rutherford had shown that the atom had a tiny, heavy, positively charged nucleus.Science Daily
Back Protons +Neutrons = Mass Number Next Protons = Atomic numberHome Number of Electrons = Number of ProtonsThe nucleus is made up of protons AND neutrons, with electrons orbiting.In a neutral atom, the number of electrons equals the number of protons.Atoms can gain or lose electrons to become charged particles called ions.Different elements have a different number of protons (atomic number).Atoms of the same element can have different number of neutrons but to remainthe same element they have to have the same number of protons.These are called isotopes. Lithium can have several numbers of neutrons for one isotope and less/more in another. Background radiation This comes from natural and artificial sources
Back Next Home Radioactive decay… • Radioactivity occurs as a result of changes in the nuclei of atoms. • A radioactive isotope is an atom with an unstable nucleus. • When it splits up (decays): • It emits alpha, beta or gamma radiation, • A different atom is formed, with a different number of protons. In Beta you lose 0 in the mass and gain 1 proton. So 6 protons turns to 7 protons, 8 neutrons goes to 7 neutrons. This is why the mass remains the same number. The proton has gained one, neutron lost one.The new atom has 2 protons (andneutrons) less than the originalatom= different element.
Back NextHome Fission and Fusion• In a nuclear power station energy is released from the nuclei of uranium atoms in a process called, ‘nuclear fission’. This energy is transformed into electrical energy.• When an atom is bombarded with a neutron: the nucleus may split, ‘fission’ into two smaller nuclei.• This can lead to a chain reaction.Uranium 235 and Plutonium 239 are used in nuclear fission.
Back Fission and Fusion• Nuclear fusion is the joining of two nuclei, forming a larger one, e.g. hydrogen -> helium• The sun is an example of nuclear fusion.• Nuclear fusion reactors are not used to produce energy in a nuclear power station because the reaction does not last long enough and they use more energy than they produce.• However, scientists continue to try and develop a practical fusion reactor because it will give another source of energy, would not produce any radioactive waste and want to show that it can be done. Home