Moving
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Physics
Moving
Physics Notes
Moving About
1.1 Identify that a typical journey involves speed changes
A typical journey is not conducted with a constant velocity, but in fact the speed changes all the time, hence there is an average speed for the journey.
1.2 Distinguish between the instantaneous and average speed of vehicles and other bodies
Instantaneous speed is the speed the vehicle is travelling at that precise moment, while average speed is the speed it is travelling over a period of time.
1.3 Distinguish between scalar and vector quantities in equations
Scalar quantities have no direction e.g. mass while vector quantities do have a direction e.g. velocity in direction of motion
1.4 Compare instantaneous and average speed with instantaneous and average velocity
Speed is a scalar and has no direction, while velocity has a direction and relates to displacement
1.5 Define average velocity as change in displacement over change in time
Average velocity is the displacement over time
2.1 Describe the motion of one body relative to another
Relative velocity of A to B= relative velocity of A to C - relative velocity of B to C
2.2 Identify the usefulness of using vector diagrams to assist solving problems
Vector diagrams need to be used to calculate displacement and the direction in motion problems
2.3 Explain the need for a net external force to act in order to change the velocity of an object
An object is not moving as it has a balanced force acting upon it, all forces cancel and hence it does not move or change velocity. An external force creates a net unbalanced force, changing its velocity.
2.4 Describe the actions that must be taken for a vehicle to change direction, speed up and slow down
A net unbalanced force is needed to change a vehicle's direction or speed
2.5 Describe the typical effects of external forces on bodies including: friction between surfaces, air resistance
Friction between surfaces create drag and an external force that pulls the vehicle back as does air resistance. In most cases these are negligible.
2.6 Define average acceleration as change in velocity over change in time and hence final velocity - initial velocity over time
Average acceleration = change in velocity/ time = final velocity- initial velocity/ time
2.7 Define the terms mass and weight with reference to the effects of gravity
Mass is the amount of matter an object has, measured in kg. Weight is the acceleration of mass due to gravity (9.8m/s2) and is measured in newtons.
2.8 Outline the forces involved in causing a change in the velocity of a vehicle when: coasting with no pressure on the accelerator, pressing on the accelerator, pressing on the brakes, passing over an icy patch on the road, climbing and descending hills, following a curve in the road
Momentum, force of gravity, force pushed up by the road, drag etc.
2.8 Interpret Newton's Second Law of Motion and relate it to the equation Net force = mass x acceleration
A force is applied to a mass when there is acceleration
2.9 Identify the net force in a wide variety of situations involving modes of transport and explain the consequences of the application of the net force in terms of Newton's Second Law of Motion
As long as a vehicle (with mass) has an acceleration it has a net force acting upon it, hence it will be changing velocity etc. If there is no acceleration, either in constant velocity or stationary, then it has no force.
3.1 Identify that a moving object possesses kinetic energy and that work done on that object can increase that energy
An object gains potential energy when work is done, e.g. lifted an object, that object has energy in it, as soon as it is moving it has kinetic energy.
3.2 Describe the energy transformations that occur in collisions
Because the vehicle has kinetic energy, it is transferred to the ground or object it collided to.
3.3 Define the law of conservation of energy
Energy cannot be lost or created, it can only be transformed
4.1 Define momentum as p= mass x velocity
Momentum= mass x velocity
4.2 Define impulse as the product of force and time
Impulse is the change in momentum, which is equal to force x change in time
4.3 Explain why momentum is conserved in collisions in terms of Newton's Third Law of Motion
For every reaction, there is an equal but opposite reaction, momentum is conserved with the other equal reaction
5.1 Define the inertia of a vehicle as its tendency to remain in uniform motion or at rest
Inertia is the tendency to remain at uniform motion or at rest.
5.2 Discuss reasons why Newton's First Law of Motion is not apparent in many real world situations
The law assumes there is no apparent loss in speed of the object having inertia, however there is friction so it does not seem apparent.
5.3 Assess the reasons for the introduction of low speed zones in build up areas and the addition of air bags and crumple zones to vehicles with respect to the concept of impulse and momentum
Low speed zones require less time to reduce the car's speed, while air bags decrease force while increasing time, and crumple zones reduce force on the occupants.
5.4 Evaluate the effectiveness of some safety features of motor vehicles
Seatbelt increases the surface area so the force is more evenly distributed over the body while it increases the time taken for the occupant to slow down, decreasing force. It also avoids the occupant colliding with interior objects.
Electrical Energy in the Home
1.1 Discuss how the main sources of domestic energy have changed over time
Wood- could be used as fuel source for heat and fire
Domesticated animals- source of mechanical energy, heavy burdens machines e.g. ploughs or grindstones
Wind/ water- Windmills
Coal- Superior energy coal, steam engine, production of steel and industry
Coal/ Gas- electrical production
Nuclear Power- electrical production
Hydro-electric- electrical production
1.2 Assess some of the impacts of changes in and increased access to, sources of energy for a community
A community could now continue activities after dark, or increase industry and economic workings with sources of energy. Communication, electrical devices could be used. However introduction of coal introduced pollution and smog.
1.3 Discuss some of the ways in which electricity can be provided in remote locations
Solar panels, portable generators
2.1 Describe the behaviour of electrostatic charges and the properties of the fields associated with them
Electrostatic charges such as protons and electrons carry an electric charge (+ and - respectively). Magnitudes are the same. Positives repel, negatives repel, both attract each other. Neutrons have no charge and do not experience electric forces.
2.2 Define the unit of electric charge as the coulomb
The SI unit for electric charge is a coulomb. The charge on an electron is approximately 1.6x10^-19. Hence one coulomb is equal to the total charge of 6.25 x 10^18 electrons/protons.
2.3 Define the electric field as a field of force with a filed strength equal to the force per unit charge at that point, E= F/q
Electric field strength= Force/ charge (Newtons/ coulomb). Electric field strength has a direction!
2.4 Define electric current as the rate at which charge flows (coulombs/ second or amperes) under the influence of an electric field
Current is the rate at which charge flows (moving charges are charge carriers). This is measured in amps (or amperes) It is the amount of current flowing when one coulomb flows through a second (coulomb per second) which is 6.25x10^18 electrons.
2.5 Identify that current can be either direct with the new flow of charge carriers moving in one direction or alternating with the charge carriers moving backwards and forwards periodically
DC (direct current) means that the charge carriers move in one direction
AC (alternating current) means that the charge carriers move back and forth periodically
2.6 Describe electric potential difference (voltage) between two points as the change in potential energy per unit charge moving from one point to the other (joules/ coulomb or volts)
The voltage or electrical potential is the different in potential energy between two points, hence joules/ coulomb (V = W/q) or force/ distance
2.7 Discuss how potential difference changes at different points around a DC circuit
Potential difference changes before and after a resistor and before and after a power supply.
2.8 Identify the difference between conductors and insulators
Conductors conduct electricity while insulators do not otherwise known as resistors.
2.9 Define resistance as the ratio of voltage to current for a particular conductor R= V/I
Ohms Law states there is a relationship between voltage current and resistance V= IR, or R= V/I
2.10 Describe qualitatively how each of the following affects the movement of electricity through a conductor, length, cross sectional area, temperature, material
Longer the length of the conductor, more resistance, larger cross sectional area, more area to pass through- less resistance, higher temperature, more resistance and the different materials affect resistance.
3.1 Identify the difference between series and parallel circuits
Series circuits have all resistors on one branch, while parallel circuits have more than two branches.
3.2 Compare parallel and series circuits in terms of voltage across components and current through them
Series- Voltage is shared, while current is the same
Parallel- Voltage is same, current is shared.
3.3 Identify uses of ammeters and voltmeters
Ammeters measure current, while voltmeters measure voltage
3.4 Explain why ammeters and voltmeters are connected differently in a circuit
Ammeters need to be in series to read the current while voltmeters are connected in series, since they need to measure the potential difference, over a section of the circuit.
3.5 Explain why there are different circuits for lighting, heating and other appliances in a house
Parallel circuits are used around the house, each with a fuse and separate circuits so that if one branch downs the others don't. Each have a maximum current for safety, no point having one circuit around the house too much current.
4.1 Explain that power is the rate at which energy is transformed from one from to another
Power= voltage x current. Hence the rate at which energy is transformed from one to another
4.2 Identify the relationship between power, potential difference and current
P= voltage x current (watts)
4.3 Identify that the total amount of energy used depends on the length of time the current is flowing and can be calculated using Energy = V x I x t
Energy = power x time, or v x I x t. It is how much power over time used. Measured in kilowatt hours.
4.4 Explain why the kilowatt-hour is used to measure electrical energy consumption rather than the joule
The joule is too small and kilowatt hour is used because it takes into account time and is much larger.
5.1 Describe the behaviour of the magnetic poles of bar magnets when they are brought close together
Like poles repel, unlike poles attract. Lines flow from North to South
5.2 Define the direction of the magnetic field at a point as the direction of force on a very small north magnetic pole when placed at that point
If like poles, repel, if unlike poles they attract
5.3 Describe the magnetic field around pairs of magnetic poles
Lines flow from north to south, in equal spacing. Pole rule applies.
5.4 Describe the production of a magnetic field by an electric current in a straight current- carrying conductor and describe how the right hand grip rule can determine the direction of current and field lines.
Using your right hand, do a thumbs up and align with diagram. Fingers curling around demonstrate the direction of current while thumb points to the magnetic field, which points to north.
5.5 Compare the nature and generation of magnetic fields by solenoids and a bar magnet
A solenoid uses an electrical current to generate a magnetic field while a bar magnet already has a magnetic field.
6.1 Discuss the dangers of an electric shock from both a 240 volt AC mains supply and various DC voltages, from appliances, on the muscles of the body.
The higher the voltage the more severe the shock. The current that flows across the heart is the most dangerous and can cause fibrillation which causes the heart's muscle to oscillate rapidly screwing up the normal process. Alternating current can cause fibrillation while DC does not. Most dangerous electrocution is hand to hand or hand to opposite foot as the current passes through the heart. Foot to foot is least dangerous. The dryness of the skin determines resistance and can reduce the voltage or severity, however wet skin due to sweat lowers this dramatically.
6.2 Describe the functions of circuit breakers, fuses, earthing, double insulation and other safety devices in the home.
These devices prevent overloading of a circuit and thus prevent fires from overheating, or damage to the device. Earthing is used so that if a person touches the object that is not earthed they will be electrocuted.
The World Communicates
1.1 Describe the energy transformations required in one of the following: mobile telephone, fax/modem, radio and television
Mobile telephone: Sound energy- transformed to electrical energy- microwaves- electrical energy- sound energy
1.2 Describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium
A wave is a carrier of energy through the motion of particles. Wave down a slinky (one), pebble dropped in water (two), sound emitted from a speaker (three)
1.3 Identify that mechanical waves require a medium for propagation while electromagnetic waves do not
Mechanical waves require a medium while an electromagnetic does not, sound cannot travel through a vacuum, but light can.
1.4 Define and apply he following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction, crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity
Medium- the material the wave is travelling through, displacement- distance a particle is away from the equilibrium, amplitude- the maximum displacement of the particle, period- the time it takes for one wave to pass through a fixed point, compression- areas in a longitudinal wave where particles are compressed, rarefactions- areas in a longitudinal wave that are not compressed, crest- highest part of a wave, trough- lowest point of a wave, transverse waves- the direction of particle motion is perpendicular to the direction of wave propagation, longitudinal waves- the direction of particle motion is parallel to the direction of wave propagation, frequency- the number of waves that pass through a fixed point in one second, wavelength- distance between two adjacent points on a wave, velocity- the speed of a wave in metres per second
1.5 Describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves
Transverse- direction of particle motion is perpendicular to direction of wave propagation
Longitudinal- direction of particle motion is parallel to direction of wave propagation
1.6 Quantify the relationship between velocity, frequency and wavelength for a wave (velocity= frequency x wavelength)
Velocity is directly proportional to frequency and wavelength, velocity= frequency x wavelength
2.1 Identify that sound waves are vibrations or oscillations of particles in a medium
Sound waves are waves that transmit energy through vibrations/ oscillation of particles in a medium
2.2 Relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves used to represent them
The middle of a compression equates to a crest and the middle of a rarefaction equates to a trough
2.3 Explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves
The higher the pitch, the higher the frequency, while the higher the volume, the larger the amplitude and vice versa
2.4 Explain an echo as a reflection of a sound wave
An echo is a reflection of a sound wave of a surface, where the wave is reflected off the surface, resulting in an echo
2.5 Describe the principle of superposition and compare the resulting waves to the original waves in sound
Superposition is when two waves are in phase and for a brief moment, when they collide the resulting wave doubles, then returns to normal. If the same happens for two waves out of phase, then they cancel each other out.
3.1 Describe electromagnetic waves in terms of their speed in space and their lack of requirement of a medium for propagation
All electromagnetic waves travel at the speed of light which is 3.0x 10^8 metres per second. All can travel through a vacuum as they are not mechanical waves.
3.2 Identify the electromagnetic wavebands filtered out by the atmosphere, especially UV, X-rays and gamma rays
UV, X-rays and gamma rays, in particular waves of high frequency get filtered out by the atmosphere
3.3 Identify methods for the detection of various wavebands in the electromagnetic spectrum
Communication technology, machines
3.4 Explain the relationship between the intensity of electromagnetic radiation and distance from a source is an example of the inverse square law.
For every metre you stand back from a source, the inverse square is the drop in radiation
3.5 Outline how the modulation of amplitude or frequency of visible light, microwaves, and or radio waves can be used to transmit information
AM and FM use amplitude and frequency to transmit information
3.6 Discuss problems produced by the limited range of the electromagnetic spectrum available for communication purposes.
Not all EM waves can be used for communication, waves carry varying amounts of data with other problems like range, security and interference.
4.1 Describe and apply the law of reflection and explain the effects of reflection from a plane surface on waves
Law of reflection, angle of incidence = angle of reflection
4.2 Describe ways in which applications of reflection of light, radio waves and microwaves have assisted in information transfer
Fibre optics, radio, mobile phones
4.3 Describe one application of reflection for each of the following: plane surfaces, concave surfaces, convex surfaces, radio waves and being reflected by the ionosphere.
Mirrors, headlights, safety mirrors, long range transmission of AM waves
4.4 Explain that refraction is related to the velocities of a wave in different media and outline how this may result in the bending of a wavefront
The velocity of light slows down as it enters a new medium, causing the wave to bend as one side slows down
4.5 Define refractive index in terms of changes in the velocity of a wave in passing from one medium to another
A ratio of the speeds or sin angles of medium
4.6 Define Snell's Law
Velocity of light over velocity of material= sin (angle of incidence) over sin (angle of refraction)
4.7 Identify the conditions necessary for total internal reflection with reference to the critical angle
Total internal reflection occurs when angle of incidence is greater than critical angle, critical angle occurs when angle of refraction is 90 degrees
4.8 Outline how total internal reflection is used in optical fibres.
The light transfers information which is continuously reflected through total internal reflection
Cosmic Engine
1.1 Outline the historical development of models of the Universe from the time of Aristotle to the time of Newton
Aristotle- developed geocentric model because it was common sense that the Earth was fixed and not moving
Aristarchus- proposed heliocentric model
Ptolemy- added epicycles to account for retrograde motion and varying brightness of planets, good predictions
Copernicus- developed heliocentric model
Galileo- proved the Copernican model through the telescope. Looked at phases of Venus and moons of Jupiter.
Brahe- had a mixture of geocentric and heliocentric model. Made accurate predictions
Kepler- Brahe's assistant, developed his three laws
Newton- Universal Gravitational Law, the force between any mass in the universe
2.1 Outline the discovery of the expansion of the Universe by Hubble, following its earlier prediction by Friedmann
Friedmann proved Einstein was wrong, the universe was expanding. Hubble discovered red shift implying that everything was moving away from everything else. Hence it was an expanding universe.
2.2 Describe the transformation of radiation into matter which followed the Big Bang.
Radiation cooled down to form quarks and then atoms, which then formed matter
2.4 Identify that Einstein described the equivalence of energy and mass
E= mc2 which says that energy can be converted to mass and vice versa.
2.5 Outline how the accretion of galaxies and stars occurred through, expansion and cooling of the Universe, subsequent loss of particle kinetic energy, gravitational attraction between particles, lumpiness of the gas cloud that then allows gravitational collapse
The Universe expanded and then cooled, allowing radiation to form particles, which then cooled. Over time it slowed down to clump together, forming gravitational attraction, these centre of gravity formed gas clouds which got so hot, nuclear fusion occurred, causing stars to form and hence galaxies formed through accretion.
3.1 Define the relationship between the temperature of a body and the dominant wavelength of the radiation emitted from that body
A body emits a certain wavelength (which is dominant that defines its colour). The hotter a body, the more shifted the spectrum to the left. A black body absorbs all radiation and emits EMR
3.2 Identify that the surface temperature of a star is related to its colour
Hotter a star, more blue, white, while a cooler star is more orange red.
3.3 Describe a Hertzsprung- Russel diagram as the graph of a star's luminosity against its colour or surface temperature
In the middle there is the main sequence stars, with giants and supergiants above the sequence, while white dwarfs are below the main sequence.
3.4 Identify energy sources characteristic of each star group, including Main Sequence, red giants and white dwarfs
Main Sequence, usually yellow in the colour and medium sized, red giants cool but huge stars and are very luminous and white dwarfs are small but very hot, not luminous.
4.1 Identify that energy may be released from the nuclei of atoms
Energy release from the nuclei of atoms can be in one of three forms of radiation, alpha, beta or gamma
4.2 Describe the nature of emissions from the nuclei of atoms as radiation of alpha and beta particles and gamma rays in terms of ionising power, penetrating power, effects of magnetic field, effect of electric field
|
Alpha |
Beta |
Gamma |
Nature |
Helium nucleus |
Electron |
Electromagnetic Radiation |
Ionising Power |
High |
Medium |
Low |
Penetration |
Low |
Medium |
High |
Magnetic Field |
Moderate |
Highly affected |
Not affected |
Electric Field |
Moderate |
Highly affected |
Not affected |
4.3 Describe the particulate nature of the solar wind
The solar wind is made of hot plasma, which consists of ions, protons and electrons. Travels at 400-500 km/h
4.4 Outline the cyclic nature of sunspot activity and its impact on Earth through solar winds
Sunspot activity is cyclic and peaks every 11 years, with sunspots, flares and coronal mass injections increasing- which disrupt electromagnetic communication and electrical grids.
4.5 Describe sunspots as representing regions of strong magnetic activity and lower temperature.
Sunspots are regions on the surface of the sun that have an intense magnetic activity and lower temperature. They form due to the locations of disturbances in the magnetic field lines of the Sun's surface.
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