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# Density , pressure & temperature

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### Density , pressure & temperature

1. 1. DENSITY Density is all about the compactness in molecular arrangement in any substance which decides how heavier or lighter any substance is! DENSITY is a physical property of matter, as each element and compound has a unique density associated with it. Density defined in a qualitative manner as the measure of the relative "heaviness" of objects with a constant volume. For example: A rock is obviously more dense than a crumpled piece of paper of the same size. A styrofoam cup is less dense than a ceramic cup. Density may also refer to how closely "packed" or "crowded" the material appears to be - again refer to the styrofoam vs. ceramic cup. Let us Consider ice cubes on the water we could see ice floats on water which tells us that water is denser than ice. Density is calculated using the below formula. It is represented by ρ. Weight Density formula is given by The Density is expressed in Kg/L. The Density Formula is used to determine the density of any given body. Density Problems Examples ; Question 1: Find the density of water if it has mass of 1000 Kg and Volume of 1m3 ? Solution: Density is given by formula ρ = MassVolume = 1000Kg1m3 = 1000 Kg/m3 . Question 2: Find the Volume of the container if it can hold 150 Kg of oil having density of 890 Kg/m3 ? Solution: Given: Mass m = 150 Kg, Density ρ = 890 Kg/m3 , Volume V = mρ = 150Kg890Kg/m3 = 0.168 m3 .
2. 2. PRESSURE Pressure is defined as force per unit area. It is usually more convenient to use pressure rather than force to describe the influences upon fluid behavior. The standard unit for pressure is the Pascal, which is a Newton per square meter. For an object sitting on a surface, the force pressing on the surface is the weight of the object, but in different orientations it might have a different area in contact with the surface and therefore exert a different pressure. Pressure Calculation There are many physical situations where pressure is the most important variable. If you are peeling an apple, then pressure is the key variable: if the knife is sharp, then the area of contact is small and you can peel with less force exerted on the blade. If you must get an injection, then pressure is the most important variable in getting the needle through your skin: it is better to have a sharp needle than a dull one since the smaller area of contact implies that less force is required to push the needle through the skin. When you deal with the pressure of a liquid at rest, the medium is treated as a continuous distribution of matter. But when you deal with a gas pressure, it must be approached as an average pressure from molecular collisions with the walls. Pressure in a fluid can be seen to be a measure of energy per unit volume by means of the definition of work. This energy is related to other forms of fluid energy by the Bernoulli equation.
3. 3. TEMPERATURE Fahrenheit and Celsius Conversion Formulas Fahrenheit to Celsius: Celsius to Fahrenheit: Temperature Scales The degree Fahrenheit (°F) is a unit of temperature named for the german physicist Gabriel Fahrenheit (1686 - 1736). In the Fahrenheit scale of temperature the freezing point of water is 32 degrees and the boiling point is 212 degrees placing the boiling and melting points of water 180 degrees apart. Zero degrees Fahrenheit indicates the lowest temperature Fahrenheit could obtain by a mixture of ice and salt. The degree Celsius (°C) is a unit of temperature named for the Swedish astronomer Anders Celsius (1701-1744) who first proposed it. The Celsius temperature scale was designed so that the freezing point of water is 0 degrees and the boiling point is 100 degrees at standard atmospheric pressure. Since there are one hundred steps between these two reference points the original term for this system was Centigrade (100 parts). Examples How many degrees Celsius are 68 degrees Fahrenheit? Replace Fahrenheit with 68 and solve for Celsius: C = (68 - 32) * 5/9 Replace F by 68 in C = (F - 32) * 5/9 C = 36 * 5/9 Simplify C = 20 20 °C = 68 °F At what temperature are Celsius and Fahrenheit temperatures equal? Replace both temperatures with "T" in one of the equations above and solve for T: T = T * 9/5 + 32 Subtract 32 from both sides T - 32 = T * 9/5 Subtract T from both sides (Note that T * 9/5 is the same as T + T * 4/5) -32 = T * 4/5 Multiply both sides by 5 -160 = T * 4 Divide both sides by 4 -40 = T -40 °C = -40 °F