HOW PRESSURE IS EXERTED BY LIQUID AND GASES?

HOW PRESSURE IS EXERTED BY LIQUID AND GASES?

Activity 11.8: ( pressure depends height of water )

*   Take a transparent glass tube or a plastic pipe. The length of the pipe/ tube should be about 25 cm and its diameter should be 5-7.5 cm.

*   Also take a piece of a thin sheet of good quality rubber, say, a rubber balloon.

*   Stretch the rubber sheet tightly over one end of the pipe. Hold the pipe in the middle, keeping it in a vertical position (Fig.11.14).

*   Ask one of your friends to pour some water into the pipe.

*   Does the rubber sheet bulge out? Note also the height of the water column in the pipe.

*   Pour some more water. Observe again the bulge in the rubber sheet and the height of the water column in the pipe.

*   Repeat this process a few more times.

*   Can you see any relation between the amount of the bulge in the rubber sheet and the height of the water column in the pipe?

Figure 11.14: Pressure exerted by water at the bottom of the container depends on the height of its column

Activity 11.9: ( pressure at walls of container )

*   Take a plastic bottle. You can take a discarded water or soft drink bottle.

*   Fix a cylindrical glass tube, a few cm long near its bottom as shown in Fig. 11.15.

*   You can do so by slightly heating one end of the glass tube and then quickly inserting it near the bottom of the bottle.

*   Make sure that the water does not leak from the joint. If there is any leakage, seal it with molten wax.

*   Cover the mouth of the glass tube with a thin rubber sheet as you did in Activity 11.8.

*   Now fill the bottle up to half with water. What do you observe?

*   Why does the rubber sheet fixed to the glass tube bulge this time?

*   Pour some more water into the bottle. Is there any change in the bulge of the rubber sheet?

Figure 11.15: A liquid exerts pressure on the walls of the container

Note that the rubber sheet has been fixed on the side of the container and not at the bottom. Does the bulging of the rubber sheet, in this case, indicate that water exerts pressure on the sides of the container as well? Let us investigate further.

Activity 11.10: ( equal pressure at same depth )

*   Take an empty plastic bottle or a cylindrical container.

*   You can take a used tin can or a used plastic bottle.

*   Drill four holes all around near the bottom of the bottle.

*   Make sure that the holes are at the same height from the bottom (Fig. 11.16).

*   Now fill the bottle with water. What do you observe?

*   Do the different streams of water coming out of the holes fall at the same distance from the bottle?

*   What does this indicate?

Figure 11.16: Liquids exert equal pressure at the same depth

Can you now say that liquids exert pressure on the walls of the container?

Do gases also exert pressure? Do they also exert pressure on the walls of their containers? Let us find out.

When you inflate a balloon, why do you have to close its mouth? What happens when you open the mouth of an inflated balloon? Suppose you have a balloon that has holes. Would you be able to inflate it? If not, why? Can we say that air exerts pressure in all directions?

Do you recall what happens to the air in the bicycle tube when it has a puncture? Do these observations suggest that air exerts pressure on the inner walls of an inflated balloon or a tube? So, we find that gases, too, exert pressure on the walls of their container.

You have seen fountains of water coming out of the leaking joints or holes in pipes supplying water. Is it not due to the pressure exerted by water on the walls of the pipes?

Source: This topic is taken from NCERT TEXTBOOK