Page 159 - Physics

Pressure

Now, what happens if all the trapped The cardboard does not fall when the glass
air inside the hemispheres is removed? tumbler is inverted due to the atmospheric
On removal of air from inside, a partial pressure acting upwards on the cardboard.
vacuum is created inside the sphere. Thus, Atmospheric pressure is higher than that
the external atmospheric pressure exerts of the water acting downwards on the
a large unbalanced force and presses the cardboard.
spheres tightly together. Therefore, it
becomes very diffi cult to pull the half- Acti vity 7.5
spheres apart. Aim: To demonstrate the
existence of atmospheric
Acti vity 7.4 pressure using a crushing
can.
Aim: To demonstrate the
existence of atmospheric Materials: Empty tin, hot water, cold
pressure using water in a water and cork
tumbler. Procedure
Materials: Glass tumbler or test 1. Pour a small quantity of hot water
into a can and boil for a few minutes
tube, cardboard, water and while the can is open to drive off the
plunger air, as shown in Figure 7.27 (a).
Procedure 2. Stop boiling and then close the can
1. Fill a glass tumbler with water and tightly with the cork.
place the cardboard fi rmly on top 3. Pour some cold water over the can to
of the glass so that there is no air cool it as in Figure 7.27 (b).
between the glass and the cardboard.
2. With your hand on the cardboard, Can opened
gently turn the tumbler upside down,
as shown in Figure 7.26, then, remove
your hand from the cardboard.
3. Record your observations.
Heat applied

(a)
Cold water
Water
Glass tumbler Can closed
Cardboard
Figure 7.26 Atmospheric
Questions pressure
(a) Explain why the cardboard does
not fall when the glass tumbler is
inverted. (b)
(b) Explain your observations. Figure 7.27

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Physics Form 1 Final.indd 153 16/10/2024 20:57