Measurements

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1.general physics  1.1 length and time  -i-Physical Quantity Physical Quantities A physical quantity is a property of an object that can be measured with a measuring instrument. A physical quantity is usually expressed as “a magnitude ( numerical value)  and a  physical unit or more ” Example :- Normal body temperature of a healthy human being is  37  0 C -ii-Length Measuring Length. Length is “the distance between two points in a space”. According to SI units, the length quantity is expressed in meter. There are several kinds of measuring devices used to measure quantity of length, among others, are as follows. Tools used… a-   Measuring tape. b-   Ruler c-   Vernier callipers. d-    Micrometer Measurement of length Length is measured accurately through many methods. Here are some: Method Notes Ruler Used to make simple measurements accurate to  0.1 cm  (1 mm) Vernier caliper Used to make simple measurements accurate to
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Sound

Sound

Production: sound waves come from a vibrating source for example a loudspeaker. As the loudspeaker cone vibrates, it moves forwards and backwards, which squashes and stretches the air in front. As a result, a series of compressions (squashes) and rarefactions (stretches) travel out through the air, these are sound waves.
Sound waves are longitudinal: they have compressions and rarefactions and oscillate backwards and forwards. 


  • approximate range of audible frequencies for a healthy human ear is 20 Hz to 20000 Hz 

    Ultrasound : sound or other vibrations having an ultrasonic frequency, particularly as used in medical imaging.


    Sound waves need a medium (a material) to travel
    through
    Compression: high pressure section of the wave
    Rarefaction: low pressure section of the wave 

     Sound travels faster in liquids than in gasesbecause molecules are more tightly packed. ... Sound travels fastest through solids. This is because molecules in a solid medium are much closer together than those in a liquid or gas, allowing sound waves to travel more quickly through it.

    Speed of sound is highest in solids (concrete: 5000m/s) then in liquids (pure water: 1400m/s) and slowest in gases (air: 330m/s).




    Experiment: When sound reflects off of a wall, it will
    come back to you. This is what you hear as an     echo.
    If you know the distance between you and the wall,
    and measure how long it takes for the echo to sound,
    you can figure out the speed of sound in air.
    Remember to take into account that the sound has
    gone there and back
    •Higher frequency → a higher pitch
    Larger amplitude → louder sound


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