Playing Card Showdown

What you need

  • A pack of cards.
  • A top hat. If you don't have a top hat, find a friendly Victorian gentleman and ask if you can borrow his. If that doesn't work, try an inferior sort of hat or - at a pinch - a cardboard box or saucepan. Just so long as the opening is fairly close to the ground, and about 15-20 cm wide.

What you do

  1. Try to drop the cards from approximately waist height into the hat. Go on, have a go.
  2. No luck? Try challenging somebody else to do it.
  3. They're not managing, either, eh? Shame. OK, skip ahead to the explanation, then come back here and offer them some sort of bet. Maybe they'll tidy your bedroom if you can drop five cards in a row into the hat?
  4. Then proceed to drop every card, one after the other, into the hat. Which you can do, now you know the knack.

What's going on?

As you drop them the playing cards appear to defy gravity. Cards dropped horizontally fall slowly while those dropped edge on don't even fall straight to the ground. They are clearly experiencing other forces due to the air they are passing through. If there was no air, both cards would fall straight to the ground.

As the cards fall, the force of gravity is pulling on each card seemingly from a single point - its centre of mass. The motion of the air around the card creates vortices - tiny swirls of air - which add an uneven resistance at varying places over the surface of the card.

Once dropped the horizontal card may tip slightly, but the tipping motion creates a vortex off the lowest edge of the card, which increases the resistance to motion at this point of the card. The result is the card re-stabilises back in the horizontal position.

The card dropped vertically starts off in an unstable position. Once a slight deviation from the vertical occurs, the card starts to turn. In this case, when it reaches the horizontal position (seemingly stable) the card has so much rotational momentum that it keeps on turning. And, instead of tumbling down in a straight line towards the open hat, a combination of the uneven resistance forces cause the card to tumble and flutter in the air, and move away from its straight downward path.

The conclusion? If you want to get your card in the hat, start in the stable position - with the card held horizontally.