Page 142 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

How can the expansion of balloon be related to the depth
of the level of liquid in the pipe?
Haven’t you understood that the pressure experienced in
liquids depend on the height of the liquid column above it?
Pour more water in the pipe to raise the water level in it. Haven’t
you understood why the balloons expanded more?

The pressure exerted by a liquid column increases with increase in
height.

The thrust acting per unit area by a liquid is liquid pressure.
Liquids exert force on all sides of the container in which they are taken.

Haven’t you seen that the height of the liquid column influences
the pressure exerted by it? Try to do one more experiment.
Firmly fix two identical balloons at the lower ends of two
identical PVC pipes as shown in Figure 10.14.

Now fill one of the pipes with water and the other with kerosene.

What do you observe?
Why is the expansion of balloons different? Discuss.

From the experiments we have done so far, let’s list the factors
influencing liquid pressure:
Fig. 10.14
height of the liquid column (h)

density of the liquid (d)
In other words, liquid pressure is directly proportional to the
weight of liquid column over unit area.

If the height of the liquid column is ‘h’, density of liquid ‘d’ and
acceleration due to gravity ‘g’, then liquid pressure is P = hdg

Can gases exert pressure similar to liquids? Let’s examine.
Atmospheric Pressure

Burn a few pieces of paper and put it in a tall glass bottle. Peel
a fully ripe banana a little and place it at the mouth of the bottle,
when the paper has almost burnt. What do you observe? What
might be the reason?

What happens to the pressure of air inside the bottle when
Fig. 10.15
the paper burns?

Basic Science VIII 141