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# Mechanics Definitaio

### Physics definitions

TermDefinition
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
Created by: Nya411

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