Atmospheric Pressure

As we know that ;

Hence, we can see from above formula that pressure depends on the surface area () that means,

The less is the surface area, the greater is the pressure produced. Hence knives and blades have sharp edges because sharp edges have less surface area due to which we can get more pressure and object can be cut easily with less force.

We know that pressure depends on the surface area ().The large is the surface area less is the pressure produced. Therefore the ski-boards are long and broad to increase the surface area, which reduces the pressure on snow and we will not sink in snow.

Ink enters the dropper till the pressure of the air inside the dropper becomes equal to the atmospheric pressure outside acting on the ink in the bottle. It is because the two pressures ( atmospheric pressure, Pressure of air in the dropper) are equal the ink does not spill out unless the bulb is pressed, because on pressing the bulb the pressure inside the dropper becomes more than atmospheric pressure thus the two pressures are not equal.

(a) The unit of pressure is N\m²(Newton Per meter square).

Since Standard (S.I) unit of force is Newton(N) and of area is meter square(m²) .And As we know that

Hence Standard (S.I) unit of pressure is N/m² (Newton per meter square).

(b) Ink rises into the ink dropper because of the atmospheric pressure acting on the surface of the ink in the bottle.

On pressing the bulb of the dropper the air inside the dropper is pushed out of the hole in the dropper. This makes the pressure of the air in the bulb less than the atmospheric pressure. Hence to make the pressure inside the bulb equal to the atmospheric pressure outside, the ink rises in the dropper.

(c) When the piston of a pump is pulled up, the pressure inside Decreases.

When the piston of the pump is pulled up all the air inside the pump is pushed outside through the narrow tube, this reduces the pressure inside the piston. Due to this reduced pressure only the water comes inside the pump so that pressure inside the pump becomes equal to the atmospheric pressure outside.

(d) The air pressure inside our body is equal to the Atmosphericpressure.

The atmosphere exerts a pressure called as the atmospheric pressure. We do not get crushed by the pressure because the atmospheric pressure inside our body is equal to the atmospheric pressure outside.

(a) True

When the air is filled inside the balloon the pressure inside the balloon increases and the balloon becomes spherical and exerts equal pressure in all directions in order to balance the atmospheric pressure. Figure below illustrates the following.

(b) True

In order to make the pressure equal both sides the fluids always flows from the higher pressure to lower pressure( this makes pressure difference equal to zero), once the pressure becomes equal both sides the flow of the fluid stops. Therefore the above statement is True.

(c) False

As we know that ;

Hence we can see from above formula that pressure depends on the surface area () that means,

Hence less is the surface area, the greater is the pressure produced.

Therefore the above statement is False.

(d) True

When we stand on a cane chair the area of contact (surface area)with the chair is less , hence the pressure exerted on the chair due to the weight is more . And this increased pressure increases the possibility of breaking the cane chair due to more force.

The glass stands on the three coins and the water does not come out of the glass because of the Atmospheric pressure.

Here is the Experiment along with the images.

1) Place a dish upside down on the glass filled with the water as shown in the figure.

2) Now gently slide the coin under the glass without disturbing water.

3) Push three coins under the glass in a way similar to first coin as shown in the figure below.

OBSERVATION: You will see that the glass is standing on the three coins. And the water does not spill out of the glass.

WHY THIS HAPPENS: There is no such magic which has happened; it is due to the atmospheric pressure. When we have gently pushed the coins under the glass the air inside the glass comes out which reduce the pressure inside the glass and pressure becomes less than the atmospheric pressure outside the glass. Therefore the atmospheric pressure exerts the force on the glass thus due to the force exerted by the atmospheric pressure the water does not come out of the glass.