Hooked on Science: The floating mystery

Why wouldn't two same-size cups act the same way in water? Find out with a few materials from around the house.

Materials

* 16 ounce Styrofoam cup

* 16 ounce clear plastic cup

* Water

* Large transparent container

Instructions

STEP 1: Fill the large transparent container three-fourths of the way with water.

STEP 2: Stand the 16-ounce Styrofoam cup up in the water and observe.

STEP 3: Stand the 16-ounce clear plastic cup up in the water and observe.

Explanation

The Styrofoam cup is composed of more than 90 percent air, which makes it light weight and buoyant. This causes the Styrofoam cup to float on the water. Also, water does not easily attract to the sides of the Styrofoam cup, keeping it upright, which helps the surface tension of the water remain intact. Surface tension happens when water molecules cling to each other. The water easily attracts to the sides of the clear plastic cup. This causes the cup to break the surface tension as it falls into the water. The clear plastic cup then fills with water and sinks each time.

Jason Lindsey is a science outreach educator with Hooked on Science. Check out his website hookedonscience.org for webcasts and experiments that might get you hooked on science.