Science is Magic

69

SCIENCE

PART...

THE

Tilt the blow-dryer

a little to the side.

Amazingly, the ball

will stay in the

stream of air and

not drop down.

2

Here’s another way of seeing the Coandă

effect in action. Place a bottle in front of a

paper pinwheel and blow directly at the bottle.

The pinwheel will turn because the air from

your breath sticks to the bottle and curves

around it to move the sails. Cool, huh?

FORCE OF

GRAVIT Y

FORCE OF

THE AIR

NOW TRY THIS

The secret behind what’s going on

here has to do with balancing forces.

Gravity—the force that pulls us toward the

ground—pulls the ping-pong ball downward,

while the force of the blow-dryer’s stream of air

pushes the ball upward. When these forces

are exactly balanced, the ball doesn’t move

up or down. You may wonder why the ball

doesn’t’ “fall off” when you tilt the blow-

dryer. This is because of something called

the Coandă effect—when air moves over a

surface, it will stick to that surface a little.

So the air streaming past the ping-pong

ball sticks to it and holds it in place.

WARNING!

US_068-069_Levitating_ping_pong_ball.indd 69 12/09/2018 15:50