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Mechanics Definitaio
Physics definitions
| Term | Definition |
|---|---|
| Speed | the rate of change of distance with respect to time |
| Displacement | is the distance in a given direction |
| Velocity | is the rate of change of displacement with respect to time |
| Constant acceleration | an object moves in a straight line and does not speed up or slow down |
| Average velocity (=instantaneous velocity) | to a high degree of accuracy provided the average velocity is measured over a very small time interval or a very small distance |
| Acceleration | is the rate of change of velocity with respect to time |
| Acceleration due to gravity | in the absence of air resistance all objects near the earth's surface if released will fall downwards with the same acceleration |
| Scalar quantity | a quantity that has magnitude only and no direction |
| Vector quantity | a quantity that has both magnitude and direction |
| Force | anything that causes the velocity of an object to change (i.e. speed up, slow down or change direction) |
| Mass of a body | is a measure of how difficult it is to accelerate that body |
| The Newton | is the force that gives a mass of 1kg an acceleration of 1m/s^2 |
| Weight | of an object is the force of the earth's gravity acting on it |
| Momentum | mass times velocity |
| Density of a substance | is its mass per unit volume |
| Pressure | is force per unit area |
| moment of a force about an axis | is equal to the magnitude of the force multiplied by the perpendicular distance from the axis to the line of action of the force |
| Couple | two parallel forces with the same magnitude acting in opposite directions |
| Work | when a force (f) moves a body through displacement (s) in the direction of the force, the work (W) done is equal to the force multiplied by the displacement: work = force x displacement) |
| The Joule | is the work done when |
| Energy | is the ability to do work. The amount of energy something has is the amount of work it can do |
| Kinetic energy | the energy a body has due to its motion |
| Potential energy | the energy a body has due to its position in a force field |
| Renewable source of energy | a source of energy that does not get used up |
| Power | is the rate at which energy is converted from one form to another |
| Angular Velocity | is the rate of change of angle with respect to time |
| Centripetal Force | when a body is moving in a circle the force towards the centre needed to keep it moving |
| Centripetal Acceleration | if a body is moving in a circle the acceleration it has towards |
| Period of an orbit (periodic time) | the time taken for a satellite to go once around the central body |
| Temperature | is the measure of the hotness or coldness of a body |
| Thermometric property | any physical property that changes measurably with temperature |
| Heat Capcity | of an object is the heat energy needed to change its temperature by 1 kelvin |
| Specific heat capacity | of a substance is the heat energy needed to change the temp of 1kg of that substance by 1 kelvin |
| Latent Heat | of a substance is the heat energy needed to change its state without a change in temperature |
| Specific Latent Heat | of a substance is the heat energy needed to change the state of 1kg of that substance without a change in temperature |
| Specific Latent Heat of fusion | of a substance is the heat energy needed to change 1kg of that substance from a solid to a liquid without a change in temperature |
| Specific Latent Heat of Vaporisation | of a substance is the amount of energy needed to change 1kg of that substance from a liquid to a gas without a change in temperature |
| Conduction | is the movement of heat energy through a substance by the passing on of molecular vibration from molecule to molecule with no overall motion of the substance |
| Convection | is the transfer of heat through a fluid by means of circulating currents of fluid caused by heat |
| Radiation | is the transfer of heat energy from one place to another in the form of electromagnetic waves |
| U-value | of a structure is the amount of energy conducted per second through 1m^2 of that structure when a temperature difference of 1°C is maintained between its ends |
| Solar Constant | the average amount of the suns energy falling per second perpendicularly on 1m^2 of the Earth's atmosphere. |
| Travelling Mechanical wave | is a disturbance carrying energy through a medium without any overall motion of that medium |
| Travelling wave | either mechanical or electromagnetic is a disturbance that travels out from the source producing it, transferring energy from the source to other places through which it passes |
| Transverse wave | is a wave where the direction of vibration is perpendicular the the direction in which the wave travels |
| Longitudinal wave | is a wave where the direction of vibration is parallel to the direction in which the wave travels |
| Reflection (of waves) | is the bouncing of waves off an obstacle in their path |
| Refraction (of waves) | the changing direction of a wave when it enters a region where its speed changes |
| Diffraction | the sideways spreading of waves into the region beyond a gap or around an obstacle |
| Interference | when waves from two sources meet, a new wave is produced. The displacement produced at any point by this wave is the algebraic sum of the displacements that each wave would produce on its own |
| Constructive interference | when waves from two sources meet and the amplitude of the resulting wave is greater than the amplitudes of each of the individual waves |
| Destructive interference | when waves from two sources meet and the amplitude of the resulting wave is less than the amplitude of each of the individual waves |
| Coherent Sources | two sources of periodic waves are said to be coherent if they are in phase or if there is a constant phase difference between waves from each of the sources. Sources must also have the same frequency |
| Interference Pattern | the resulting wave pattern formed when waves from two (or more) coherent sources meet |
| Stationary Wave | when two periodic travelling waves of the same frequency and amplitude moving in opposite directions meet, they interfere with each other and the resulting wave is a stationary wave |
| Overtones | frequencies which are multiples of a certain frequency. 2f is the first overtone |
| Harmonics | frequencies which are multiples of a certain frequency. f is the first harmonic |
| Loudness | of a sound depends on the amplitude of the sound wave. The greater the amplitude the greater the loudness |
| Pitch | of a note depends on frequency. The higher the frequency the higher the pitch |
| Quality | of a musical note depends on the number of overtones present in the note and the relative strengths of the different overtones present |
| Frequency limits of audibility | are the highest and lowest frequencies that can be heard by a normal human ear. The range is 20Hz-20,000Hz |
| Resonance | if the frequency of a periodic force applied to a body is the same as or very near to its natural frequency that body will vibrate with very large amplitude |
| Sound intensity at a point | is the rate at which sound energy is passing through unit area at right angles to the direction in which the sound is travelling at that point. Sound intensity= Power/area |
| Threshold of hearing | is the smallest sound intensity detectable by the average human ear at a frequency of 1kHz |
| Sound Intensity level | is measured in decibels |
| Fundamental Frequency of a string | when a string is vibration with an antinode at its centre and a node at each end and no other nodes or antinodes. |
| The Grating Constant | the distance (d) between two adjacent slits ie the width of one line and one slit |
| Dispersion | the spreading out of the different wavelengths (colours) present in light |
| Secondary colour | the coulour formed when two primary colours are mixed in equal intensity |
| Complementary colour | a primary colour and the secondary colour that when mixed give white |
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Nya411