To demonstrate the dynamics of air pressure.
As per the principles of air pressure, a moving stream exerts less pressure than the air surrounding the moving stream and a quick air stream has a lower pressure than a slow moving one.
- Plastic straw
- Table tennis ball
Less than five minutes.
- From one end of a plastic straw cut a 10 cm piece.
- Put one end of the straw in your mouth and tip back your head.
- Hold a table-tennis ball a few inches above the other end of the straw.
- Blow as air hard as you can through the straw while releasing the ball simultaneously.
Note: The harder you blow, the higher the ball will float above the straw.
As long as you blow air through the straw, the ball remains suspended in mid-air.
The reason why the ball remains suspended in air is because it is actually ‘imprisoned’ by the column of upward rushing air. The air that is in rapid motion has a lower pressure as compared to its surroundings and owing to this, as soon as the ball moves even slightly to one side, the greater pressure outside the air stream forces it back into the fast moving air stream again.