Why do raindrops stay round on some leaves?

After rain, look closely at the leaves in a garden. On some leaves, the water sits in tiny round balls. They shine like little glass marbles, and they wobble when you touch the leaf.

On other leaves, the rain lies flat and wet. It spreads out into a thin, shiny puddle. So why do raindrops stay round on some leaves? Let's find out together.

A raindrop is made of lots of tiny bits of water. Each bit pulls on the bits next to it. They all hug in close, like friends in a tight little huddle. That pull tries to make the drop round.

A leaf can pull on water too. When a leaf grabs the water, it pulls the drop outward. The leaf's pull is stronger, so the drop spreads out flat.

The round-drop leaves are different. They wear a thin coat of wax, like the wax on a crayon. The wax makes the leaf smooth and slippery. Can you guess what the water does on that slippery wax?

Water can hardly grab hold of wax. So the waxy leaf pulls on the drop only a little. Nothing tugs the water out flat. The drop just rests there, light and loose.

Now the water's own pull wins. The drop hugs itself into a round ball and sits on top of the leaf. It looks just like the shiny marbles we saw after rain. We call a drop like this a bead, which means a tiny ball of water sitting on something.

A waxy leaf pulls on the rain only a little. So each raindrop hugs itself into a round bead.

All over the garden, the waxy leaves sparkle with raindrop beads. Each bead sits there, round and shiny, like a tiny glass marble in the sun.