National Chemistry Week - Experiments - Over the Rim

THE AIM:

To show that water likes to stick together and can even rise about the edge of its container.

WHAT YOU WILL NEED:

• 1 clear glass
• pennies (about 50 per glass)
• paper towels or a large pan

WHAT TO DO:

1. Place paper towels over your work surface. If a large pan is available, place the glass in it.
2. Fill the glass to the top with water.
3. Ask the class if they think that the glass is full. Ask them what they think will happen if you start putting pennies into the glass.
4. Proceed to gently slide pennies into the glass.
5. By looking sideways at the surface of the glass, observe that the water forms a bulge over the top of the container.

Many pennies can fit in the glass without any water spilling because water likes to stick together. When the bulge of water gets too high for all the water molecules on the surface to hold on any longer the water spills over the rim.

Insects can glide across the top of a pond without falling in because the water likes to stick together, forming a skin on the pond's surface.