PCD stands for pitch circle diameter. If there are certain number of holes are in a circle and divided equally then we say the diameter of the circle as pitch circle diameter.
To calculate the division of the PCD, multiply the diameter of the pitch circle and the given factor in the table. If 10 holes to be divided in a 100 mm pitch circle then the division, a = dia x 0.309 = 100 x 0.309 = 30.90 mm.
The speed of any objects which fall on the earth when it is simply dropped from a certain height is same without any medium (without atmospheric air). So the objects will fall to the ground at the same time. When you drop a heavy metal ball and a feather from a certain height the heavy metal ball and the feather will fall to the ground at the same time without atmospheric air (in vacuum).
Due to surface tension of the water on the surface the needle floats. Consider the water surface like an elastic rope. When a small object having less weight is kept on the rope the rope deforms down a little amount. In the same way when the needle is kept on the water surface it floats.
While we drink the water through straw we suck the air inside the draw. While we suck it some air inside the draw comes up to our mouth and there is less amount of air inside the straw in more space. So the pressure of the air is decreased inside the straw. While there is a difference in pressure the atmosphere tries to balance it. So the air outside the straw which is at high pressure tries to enter into the straw and so it pushes the water on the surface of the container. This makes the water to go inside the straw.
The earthen pot contains small pores. The water tries to go out through this holes but it gets evaporates on the outer surface of the pot. For the water to change from its liquid to vapour state it needs energy. This energy is taken from the remaining water inside the earthen pot as heat energy. So the water inside the earthen pot gets cooled.
If the tea is poured in a plate the tea will be cooled fast. But if it is in glass then it will cool slowly. From this we can understand that the surface area of the tea is less in the glass and the surface area is more in the plate. So the heat transfer easily takes place where there is more surface area. So to increase the surface area we make the hot tea poured from higher distance to lower distance and the tea cools fast.