AIR HAS PRESSURE

Explore air pressure with paper strips that move inward instead of outward, cups that "stick" to a balloon, and water that doesn't spill out of an upside-down glass.

MATERIALS:

Paper; scissors; balloon; paper, plastic, or foam cups; drinking glass; piece of cardboard or stiff paper (about 15 cm x 15 cm); water.

METHOD:1. Paper Strips: Cut two strips of paper about 22 cm x 3 cm. Take a strip in each hand and hold them facing each other, about 12 cm apart, in front of your mouth. Blow steadily between the two strips. What happens? Why?

2. Balloon and Cups: Blow up a balloon about l/3 of full size. Hold two paper, plastic, or foam cups against the sides of the balloon, and finish blowing up the balloon. How many cups can you attach to a single balloon?

3. Upside-down Glass: Fill a drinking glass about 3/4 full of water. Wet the rim of the glass. Put a piece of cardboard on top of the glass. While holding the cardboard tightly against the mouth of the glass (no air bubbles should be allowed to enter between the cardboard and the glass), turn the glass upside down. Gently let go of the cardboard. How many tries does it take before you get the water to stay in the glass? What happens if you turn the glass sideways?

Note: Air pressure plays an important role in weather. Slight, temporary changes in air pressure occur frequently. For example, when the temperature in an area drops, air molecules come closer together, thus raising the local air pressure. When the atmosphere warms, the molecules spread out, and the air pressure is lowered again. These kinds of slight changes don't usually result in major changes in the weather. Larger pressure changes, due to movements of huge low and high pressure areas, are the ones which can turn a sunny, clear day into a rainy one.

In Paper Strips, blowing between two strips of paper reduces the air pressure between the strips (flowing air exerts less pressure than stationary air). The greater pressure of the surrounding air forces the strips together. In Balloon and Cups, the pressure of the outside air is greater than the air pressure in the cups, so the cups are "pushed" onto the balloon and "stick" to it. In Upside-down Glass, the water stays in the glass because the pressure of the outside air against the cardboard is greater than the pressure of the water against the cardboard.

Topics: Air; Flight.

 

AIR ON THE MOVE

Warm air rises. Air also moves from areas of high pressure to areas of low pressure. Air in motion is wind. Use air in motion to expand a balloon. Then test for air currents.

BACKGROUND INFORMATION:

When air molecules are heated, they move faster and faster and the air expands (takes up more space). In Expanding Balloon, the hot water heats the air inside the bottle. The air expands, rises into the balloon, and makes the balloon expand. When you then cool the air in the bottle, the balloon contracts. As air expands in a closed container, the air pressure increases (air in the open atmosphere is not restricted and when it expands, its molecules move farther and farther apart, resulting in lower air pressure). Air moves from areas of high pressure to areas of low pressure. For example, air rushes out of a balloon because the pressure inside the balloon is greater than the pressure outside. Air in motion is wind. The greater the pressure difference between two areas, the stronger the wind.

Warm air rises and cool air falls. When heated air (e.g. air warmed by contact with the warm Earth) rises, it creates an updraft. When cool air (e.g. air cooled at cold, upper levels of the atmosphere) falls, it creates a downdraft. The Air Spiral enables you to test air currents around you. The movement of large air masses of different temperatures across regions of land plays a major role in the weather. On a local scale, air currents vary in different areas and at different times of the day.

Topics: Air; States of Matter.

MATERIALS:

Plastic bottle; balloon; pail or sink; hot water; different thicknesses of paper; scissors; thread.

METHOD:

1. Expanding Balloon: Put a plastic bottle in the refrigerator for a while to cool it down. Loosen up a balloon by blowing it up and then letting out the air. Stretch the end of the balloon over the mouth of the bottle. Put the bottle and balloon into a pail or sink of hot water. What happens to the balloon? Why? Then put the bottle and balloon into the refrigerator. What happens? Why?

2. Air Spiral: Cut out a circle of paper 10-15 cm in diameter. Make a small hole in the centre. Cut the circle into a spiral, as shown. Hang the spiral from a knotted piece of thread. Use the air spiral to find rising currents of warm air. If you're viewing the spiral from above, when it turns clockwise it indicates an updraft. Hold the spiral in place for about 30 seconds to take a reading. Where can you find an updraft? Try holding the spiral over a lamp that has been on for a while. Can you find a downdraft (when the spiral turns counterclockwise it indicates a downdraft)? Compare the way the spiral turns near the ground in a certain area to how it turns when you hold it as high as possible. Experiment with different thicknesses of paper and different numbers of spirals to find the best air spiral design.