Air presses too

The idea

Air exerts pressure on all objects and in all directions; the pressure exerted by the air around us is called atmospheric pressure.

Paper on a plate

A paper plate is turned upside down. You cover it with chart paper and lift the plate by the paper.

When is more effort needed to lift it?

• With the chart paper unfolded
• With the chart paper folded
• The effort is the same

Lift the plate

Open all three tabs.

Air has pressure

The weight of the covering sheet did not change, but more effort was needed with the larger sheet. So the air presses on the sheet, and the force grows with the area. Force on an area is pressure, so air exerts pressure on all objects.

Air exerts pressure on all objects, in all directions. The pressure exerted by the air around us is called atmospheric pressure.

Notes

Air exerts pressure on all objects. The pressure of the air around us is atmospheric pressure.

Check yourself

The pressure exerted by the air around us is called …

More effort is needed to lift the plate with unfolded chart paper because …

Blowing air into a balloon inflates it in all directions. This shows that air presses …

Air exerts pressure on …

• liquid pressure. Liquid pressure is exerted by liquids. Air gives atmospheric pressure.
• sound pressure. The air around us gives atmospheric pressure.
• atmospheric pressure — correct. Yes!
• air presses on a larger area of the sheet — correct. Yes!
• the sheet weighs more. The weight of the sheet did not change. The area did.
• the plate becomes heavier. The plate is the same. The air presses on a larger area.
• only upward. The balloon expands in all directions, so air presses in all directions.
• in all directions — correct. Yes!
• only downward. The balloon expands in all directions.
• only liquids. Air exerts pressure on all objects.
• only balloons. Air exerts pressure on all objects, not only balloons.
• all objects — correct. Yes!