Showing posts with label Science. Show all posts

Wednesday, September 30, 2020

What is Pressure|Pressure exeted by liquids

September 30, 2020

PRESSURE

Pressure :- The effect of force over a unit area is called pressure.

-Thrust or normal force :- The force that acts normally (perpendicular) over a surface is called trust or normal force.

* S.I. unit of pressure is Pascal (Pa).

* Pressure = Force/ Area.

• Pressure is directly proportional to the force.

- Pressure (increase) force will also (increase).

- Pressure (decrease) force will also (decrease).

• Pressure inversely proportional to the area.

- Area (increase) pressure will (decrease).

- Area (decrease) pressure will (increase).

1Pa = 1N/1m2 = 1N/m2= 1Nm2

When 1N of force acts perpendicular to the surface of unit area than the pressure is said to be 1 pascal.

- Another unit of pressure is bar, atm, etc.

• 1bar = (10)5 pascal.

RELATION BETWEEN AREA AND PRESSURE:-

SbRELATIONSHIP BETWEEN AREA A

• Area is less than pressure is greater between paper and pencil.

So, the tip of pencil easily pierce the paper.

• The area is more than the pressure is lesser between paper and the end of pencil.

So, the ends of pencil cannot pierce easily to the paper.

• It is more comfortable to wear broad heels while walking on soft surface.

• Elephants and bears have broad feet to help them walk on soft surfaces without falling.

• The width of straps of bags and suitcases is increased to reduce pressure while carrying them.

RELATION BETWEEN FORCE AND PRESSURE :-

• For the same area, when the force applied increases, the pressure increases.

• When the forces decreases, the pressure decreases.

PRESSURE EXERTED BY LIQUIDS :-

• The pressure exerted by liquid depends upon the depth of the water column.

• They exert pressure not only at the base of the container but also on its sides.

Liquid pressure varies with depth:-

• Water from the lowest hole comes out with the greatest force and falls at the maximum distance.

• Water from the topmost hole comes out with the least force and falls at the minimum distance.

* An instrument used to measure liquid pressure is called pressure gauge. The simplest form of a pressure guage is a manometer.

ATMOSPHERIC PRESSURE

- The pressure exerted by the weight of the air on an object is called atmospheric pressure.

• ALTITUDE :- The height of a place above the sea level is known as altitude.

* The scientific instrument used in meteorology to measure atmospher pressure is Barometer.

Atmospheric pressure decreases with altitude

The height and weight of the air column decreases as we go up. Therefore, the atmospheric pressure also reduces as we go to higher places. Hence, the atmospheric pressure at a place depends on its altitude.

FORCE OF ATMOSPHERIC PRESSURE

• The pressure exerted by atmosphere is very large. This was demonstrated by a German physicist and engineer, Otto von Guericke. He took two semicircular copper bowls and fitted them together to form a sphere. Then he sucked all the air from the sphere using a suction pump to create a vaccum inside the sphere. The two bowls were now held together only due to the atmospheric pressure. Then he tried to separate the two bowls by getting them pulled apart by a team of eight horses on each side. The bowls remained held tightly together due to the atmospheric pressure and did not separate. This proved the enormous force of atmospheric pressure.

Tuesday, September 29, 2020

What is physical changes and chemical changes

September 29, 2020

PHYSICAL AND CHEMICAL

CHANGES

PHYSICAL CHANGE:-

Those properties which describe the look or feel of a substance e.g., colour, hardness, density texture and phase are called physical properties. Every substance has its own characteristic physical properties that we used to identify the substance.

The physical property of a substance can change on changing conditions but the substance remains same or no new substance is created. e.g., if the water is subject to boil, the formation of bubbles show that the water is changing into a gas. The gas disappears into the air as water vapour. If this air touches the lid or plate covering the water, the water vapour will change back into droplets of water.

Therefore a physical change is one in which the substance undergoing the change is not destroyed and no new element or compound is formed. In some physical changes the properties like colour, shape, or size of the substance may change e.g. glowing of an electric bulb is a physical change, melting of ice is a physical change.

Look at the picture of water boiling and changing into steam. Steam is another form of water. Heating water did not create a new material. In changing the water from a liquid to a gas, only the state of the water is changed.

CHEMICAL CHANGE :-

Those properties which allow a chemical substance to react with other substances to transform from one substance to another are known as chemical properties for example copper has the chemical property of reacting with carbon dioxide and water to form greenish blue solid known as patena.

A chemical change is one in which the identity of the original substance is changed and a new substance or new substances are formed. In a chemical change the properties of the substance before and after the change are entirely different. e.g. souring of milk, burning of paper, burning of candle, etc.

Look at the picture of the burning candle. The wax of a candle burns into ash and smoke, The original materials are changing into something different.

Note:- A chemical change involves a change in the way the atoms in the molecules are chemically bonded to one another. A chemical bond is the force of attraction between atoms that holds them together.A methane molecule for example is made of a single carbon atom bonded to four hydrogen atoms, and an oxygen molecule is made of two oxygen atoms bonded to each. Figure given below shows the chemical change in which the atoms in a methane molecule and those in two oxygen molecules first full apart and then form new bonds with different patterns resulting in the formation of carbon dioxide and water molecules.

Therefore, we can say that any change in a substance that involves a rearrangement of the way atoms are bonded is called a chemical change.