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 meth...
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Conduction and convection

Conduction 

in non-metals - when heat is supplied to something, its atoms vibrate faster and pass on their vibrations to the adjacent atoms. In metals – conduction happens in the previous way and in a
quicker way – some electrons are free to move, they travel randomly in the metal
and collide with atoms and pass on the vibrations. 
The atoms in a substance are always vibrating. When heat is applied to a substance the heat energy is given to the atoms and they vibrate and move faster and so their kinetic energy increases. The vibrating atoms bump into neighbouring atoms and pass on their kinetic energy. These atoms then pass on their kinetic energy to atoms close to them and so on. In this way the heat energy moves through the substance.
Conduction takes place in solids, liquids and gases, but works best in solids as their atoms/molecules are located closer together.  Metals are the best solids for conducting heat. Metals have tightly packed atoms which can easily pass on their kinetic energy and also have free moving electrons. These electrons can move from the hot part of the metal to the colder part transferring the energy more quickly.

Convection 

as a fluid (liquid or gas) warms up, the particles which are warmer
become less dense and rise. They then cool and fall back to the heat source,
creating a cycle called a convection current. As particles circulate they transfer
energy to other particles. If a cooling object is above a fluid it will create a
convection current (like the freezing compartment at the top of a fridge)

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