Why does the ball move toward the water?

• When the stream of water touches the curved surface of the ball, it clings and wraps around it instead of bouncing away.

• Moving fluid clings to a curved surface and follows its shape — this is called the Coanda Effect.

As the water wraps around the ball's curve, it creates a region of lower pressure.

•  The normal air pressure on the opposite side is now relatively higher. It pushes the ball toward the water, not the water pulling the ball, but air pushing it.

• What looks like a magnetic attraction is actually a pressure difference caused by a curved surface and clinging fluid.

Why water clings to a curved surface?

• Water molecules are attracted to each other and also to many solid surfaces. When water flows past a curve, adhesion (attraction between two different surfaces) between the water and the surface keeps the water in contact rather than flying off in a straight line.

Why does the string angle prove a force is acting?

• When you hang the ball on a string above the tap stream, the string doesn't hang straight down — it leans toward the water.

• The only thing that can make a hanging string lean is a horizontal (sideways) force. The string angle is direct evidence that something is pushing horizontally.

Real-world connection

• Tap water running down the outside of a spout instead of falling freely is the Coanda Effect in everyday life — the water clings to the curved surface rather than detaching.

• Aircraft designers use the Coanda Effect to deflect thrust, control lift, and reduce drag — shaping engine exhausts and wing surfaces so that airflow clings where it's needed.

Try next

For another experiment where moving air creates a completely counterintuitive pressure result, try [The Impossible Blow] — where blowing harder keeps a ball trapped rather than pushing it away. And if you want to see the same Coanda logic applied to a pair of balloons, [The Stubborn Balloons] will produce a result that almost nobody predicts correctly the first time.