Lesson 9 – Air
(A) Find out.
Before drawing a medicine into the syringe, why is the plunger first pressed to the bottom of the barrel?
Ans: Before drawing medicine into the syringe, the plunger is first pressed to the bottom of the barrel to ensure that there is no air or any other substance in the barrel. It means that when we press the plunger down, all the air inside the syringe is pushed out. Now there is no air inside the barrel. So medicine rises inside the syringe.
(B) Think and tell.
1. Name some things of everyday use in which air is filled under pressure.
Ans: Football, bicycle tube, air cushion, air pillow, car tyres.
2. What is seen mixing with the air when wood or coal burns?
Ans: Water vapour gets mixed with the air when water boils.
3. What gets mixed with the air when water boils?
Ans: When wood or coal burns smoke is seen mixing with the air.
(C) Fill in the blanks.
1. There is ________ even in an empty container.
Ans: air
2. The air at a greater height from the earth is ________ than the air nearer to the earth.
Ans: rarer
3. If all the air were divided into five parts, the oxygen in the air would equal ________ part.
Ans: one
4. The layers of air nearer the earth bear ________ weight than the upper layers.
Ans: more