Why do ping pong balls come together when you blow inbetween them

Question

Why do ping pong balls come together when you blow inbetween them

Answer 1

Moving air has less pressure than standing air- so the moving air between the balls creates a slight vacuum which pulls them together.

Answer 2

OMG THEY DO?!?!?!!? wow thats really weird.....sorry im no help

-Kacy♥

Answer 3

The air speeds up as it goes between the balls, causing a lower pressure in that area. This causes the balls to merge since the pressure on the outer side of the balls exert a force forcing them together.

Answer 4

When you blow inbetween two things as light as ping pong balls, they begin to spin; one clockwise and the other counterclockwise.  This spin causes the balls to take paths.  The air circles/wraps around the outside of the balls, causing them to spin inward.  

Answer 5

Not only ping pong balls but pretty much all balls, especially the biological variety, just kidding.

There are two schools of thought.  The most popular one, that is taught in school is Burneulli's Principle.  

"As velocity increases, pressure decreases"  The decrease in pressure "sucks" the balls together.

The other idea is the Cuanda effect.  Cuanda, a Romanian aerodynamicist and aircraft designer, made the worlds first sucessfull modern airplane.  By modern, we mean an airplane that has the ability to rise off the ground under it's own power.  The Write Bros needed a catapault.

Anyway, the idea is that air, which has mass, and velocity will follow the contour of a surface.  If the flow is slow enough, the air can be described as laminar flow.  If the air has to make an abrupt change, then the interaction with the air itself or a surface causes turbulent flow.

An example of this is to put a candle three inches behind a softball.  Blow on the dark side of the ball and the air flow will bend around the ball and blow out the candle.

So how does relate to the ball or airfoil?  Half the weight of the ball time the velocity times velocity is the energy of the air.  When the air has to change directions, it affect the wing in an equal and opposite direction.   Since the balls are hanging, there is no gravity in the z axis, there fore the balls move toward the racing air.

Fact, the berneulli principle cannot be used to generate the lift required for an airplane.  The Cuanda effect generates most of the lift.  Few aerodynamic engineers even know this untill they start examining the formulaes use to calculate lift.

Answer 6

because they do.  

Answer 7

because of how they spin

Answer 8

This is because of the Bernoulli principle.  This says that when air speeds up the pressure gets lower.  So the pressure between the balls is less than the pressure outside the balls and the balls are pushed together.  Same principle explains why a plane flies, and why a curveball curves.

Answer 9

The same reason an airplace wing causes lift or if you blow air across the top of a sheet of paper it will cause it to lift. It's aerodynamics. The faster moving air between the ping pong balls causes lower pressure between the ping pong balls than there is in the air that is not moving on the other sides of the balls - there is lift on the balls on the faster moving air between them so they are lifted (or pulled) together.  

Answer 10

When air moves past a surface it creates a little lift. There's a little less pressure on the sides of the balls with the air moving past them than on the side with still air. It's the same principal that gives the top of an airplane wing lift.

Answer 11

Because when you blow between them the moving air creates a low-pressure area between them. So the higher pressure air on either side of the balls pushes them together.

Answer 12

as above... its not so much due to spin, because spin is rotational motion and alone does not cause translational motion of the ping pong balls.

Its due to a low pressure area caused by the rapid motion of air, Im not familiar with bernoullis principle but  I vaguely remember it, and yes this problem is similar to an example of lift.

Newtons 2nd law, shows that an unbalanced net external force will cause an acceleration.

If you witness an acceleration of any kind, there must be a net force acting.

The net force acting here is a result of the pressure difference on the outside of the balls in comparison to the pressure between them

This pressure differential results in a net force, proportional to the difference, causing the balls to accelerate.

Answer 13

Well, there are a number of principles at work here, lets see if I can help you to discover it on your own, with a bit of fun.

Usually you can take a vacuum cleaner hose and set it up to blow air, or get a friend to help you with a straw.....so if you were to go outside, hang up your ping pong balls. Now get the hose (or your friend with the straw, set to blow air between them (you might even be able to do this with a pair of larger hollow balls if using the vacuum, like the kind they sell with plastic bats.....)

Get a little talcum powder and sprinkle it lightly in front of the balls as the air is moving, and try to observe what it does as it blows the powder past the balls.  

If it is hard to see, try putting a dark color cloth across from where you are looking at the balls,, or even video tape it so you can slow down the image and see what is happening to the air as it moves.  This is a very simple sort of wind tunnel.

Try to be aware that sometimes when things move, even air, you can set up static electricity, and have some of that positive/negative attraction going on, however this should be more about the physics and what is called fluid dynamics. Yes, air is considered a fluid. In fact, you could do this with the two balls floating in water a little apart, and move the water with a straw. A little food coloring , just a drop, in front of the balls a couple inches should be nice and visible as you blow it down the middle between them!

Have fun learning!

Kay