Qu. 1 The balloon is the size it is because the pressure of the air on the inside equals the pressure of the air on the outside. The surface of the balloon is like the surface of a bubble and provides surface tension (Sullivan). The force that must be overcome when blowing up a balloon beyond the minimum of filling the natural space with air is proportional to the surface area. Pressure must be applied to the air in the balloon higher than the surrounding atmospheric pressure to blow it up any bigger, or the atmospheric pressure outside the balloon must be reduced.
Qu. 2 As the air is pumped out of the bell jar; the balloon inflates because the pressure of the air outside the balloon decreases, allowing the air inside the balloon to expand to fill the space left by the air which has been withdrawn.
Qu. 3 The balloon became round because the air pressure outside the balloon decreased and the air pressure needed to inflate the balloon is proportional to its surface area, which is at its minimum when the balloon is in the shape of a sphere (Sullivan). Less pressure is needed to inflate the balloon when it takes on this shape.
Qu. 4 As air re-enters the bell jar, the air pressure on the outside of the balloon begins to rise and exert pressure on the balloon. This continues until the pressure inside the balloon equals the pressure outside the balloon. The only way for this to happen is if the air inside the balloon contracts, and as this happens, the balloon will return to the size it was when first inserted into the bell jar.
Qu. 5 The suction cup stays attached to the base plate because a vacuum is created inside it. The pressure of the air on the outside of the cap is greater than that on the inside of the cap and this pressure keeps the cap attached to the base (IMHS).
Qu. 6 The suction cup loosens as the air is removed from the bell jar because removing the air reduces the pressure on the suction cup and allows ...