Air — Practice

Question 1

Which gas is most abundant in air, and what share does it make up?

Accepted Answer

Nitrogen, at about 78 per cent.

Question 2

Which gas of the air is needed for breathing and burning?

Accepted Answer

Oxygen, about 21 per cent of air.

Question 3

How would you show that air occupies space?

Accepted Answer

Invert an empty glass and push it into water. The water does not rise inside, because air already occupies that space.

Question 4

What causes wind?

Accepted Answer

Warm air rising because it is less dense, and cooler denser air rushing in to take its place.

Question 5

Describe an experiment that shows air has weight.

Accepted Answer

Weigh a deflated balloon on a sensitive balance, then inflate it and weigh it again. The inflated balloon is heavier, showing that the air inside has mass.

Question 6

Explain why warm air rises.

Accepted Answer

Heating makes the particles of air move faster and spread apart, so the air becomes less dense than the cooler air around it and rises through it.

Question 7

Explain the difference between weather and climate.

Accepted Answer

Weather is what the air is doing now or over a few days, such as a rainy afternoon. Climate is the average pattern of weather over many years in a place.

Question 8

Name three greenhouse gases and say what they do.

Accepted Answer

Carbon dioxide, methane and water vapour. They trap part of the heat the Earth radiates back out, instead of letting it escape into space.

Question 9

Explain why the can collapses in the crushing can experiment.

Accepted Answer

Boiling water drives the air out of the can as steam. When the sealed can is cooled suddenly, the steam condenses to a few drops, leaving almost a vacuum inside. With nothing pushing outward, the atmospheric pressure outside crushes the can.

Question 10

How does the ozone hole differ from global warming?

Accepted Answer

They are two different problems. The ozone hole is the thinning of the ozone layer, which shields us from harmful ultraviolet rays. Global warming is the trapping of the Earth's outgoing heat by greenhouse gases, raising the average temperature.

Question 11

A cold day occurs in summer. Does this disprove global warming? Explain.

Accepted Answer

No. A single cold day is weather, a short-term change. Global warming is a change in climate, the long-term average measured over many years, and one day tells you nothing about that average.

Practice — Air

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