Why do people sink in water?

It is because of what is called 'buoyant force'.

If you take a mug and try to push it inside water, you can feel a force that pushes the mug upwards. That is buoyant force.

F = v x d x g, where
F = buoyant force,
v = volume of the body,
d = density of the liquid,
g = acceleration due to gravity

Thus, in this case which you have mentioned, buoyant force primarily depends on the volume and density. More the volume, more the force. But more the volume, less the density.

Ships are in fact made of iron, steel and other metal alloys which are in fact much denser than water. But the air spaces in them increases the volume to such an extent that the overall volume increases, and the density drops (more the volume, less the density). Thus, the buoyant force also decreases, and ships float.

Human body density is in fact less than water. But the problem is that when people fall into water, they consume a lot of water which keeps the volume steady but increases the overall density. Thus, they sink. If one doesn't consume water at all, then he/she stays afloat in water.

What will happen to the reading if the bulb of a thermometer is suddenly introduced in hot water bath?

Initially there will be rise in temperature till it reaches equilibrium temperature of water temperature of bath and start falling down in case of no heat is added to water bath.

Why is the sky blue?

The atmosphere is the mixture of gas molecules and other materials surrounding the earth. It is made mostly of the gases nitrogen (78%), and oxygen (21%). Argon gas and water (in the form of vapor, droplets and ice crystals) are the next most common things. There are also small amounts of other gases, plus many small solid particles, like dust, soot and ashes, pollen, and salt from the oceans.

The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.

However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.

As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.

Universal Law of Gravitation


"Every object of the universe attracts other object .the force of attraction between them is directly proportional to product of their masses and is inversely proportional to the square of distance between them.this force is along the line joining the centre of both the objects"

Mathematical form of Newtons Universal Law of Gravitation

F (gravitational force acting) = G*m1*m2/r^2

where G is the constant , m1 and m2 are masses of the two bodies and r is the distance between them. so from this we can assume that

G= F*r^2/m1*m2

Now as the mathematical form of law of gravitation remains same at any place in universe and we derive gravitational constant from that law, so it is also constant all over universe .

Henry Cavendish found the value of G which is 6.67*10^-11.

what is the technical difference between "Gravity" and "Gravitation"?


They are often used interchangably, but gravitation often refers to the theory or concept of gravity in general, and is more often than not used in its adjectival form gravitational. Gravity often refers the gravitational field itself (a vector quantity or its magnitude). For example, being on earth, you are subject to the force of gravity. Your weight is a gravitational effect. Also, gravity tends to be the term of choice in Newton's (field) theory of gravity. Gravitation tends to be the term of choice in general relativity, in which there is no gravity field, per se.

What is Insulation Resistance, Dielectric Absorption, Polarization Index

INSULATION RESISTANCE
 Insulation Resistance is the resistance offered by insulator separating two electrodes. The value determines quality of insulation.

POLARIZATION INDEX
The ratio of the ten-minute to the one-minute measurement is known as the Polarization Index. In general, a high ratio is indicative of 'good' insulation.

DIELECTRIC ABSORPTION
Carrying out a 10-15 minute test will yield some meaningful information. Clean, dry insulation will show an increasing resistance reaching a final steady-state level, after 10 to 15 minutes. Wet or dirty insulation will reach a steady state value much sooner.