Hooked on Science: Swimmer's secret

Materials

• Racquetball
• Tennis ball
• Water
• Stopwatch

Instructions

STEP 1: Slowly pour a cup of water over the racquetball and, while observing, use the stopwatch to determine how long it takes to empty the cup of water. Record your data.

STEP 2: Slowly pour a cup of water over the tennis ball and, while observing, use the stopwatch to determine how long it takes to empty the cup of water. Record your data.

STEP 3: Using the data, determine which ball slows down the flow of water the fastest.

STEP 4: Through the observation of water flowing around each ball, provide evidence that a pattern can be used to predict the future motion of water.

Explanation

The smooth racquetball sheds the water faster when compared to the fuzzy tennis ball. The reason is friction: the resistance between two objects. Friction slows down objects. This is why swimmers cover or remove all their body hair before a race. Friction in water and air is called drag force. Drag force is created by turbulent flow in the water or air. Each hair on the body of a swimmer creates a pool of turbulence in the water, slowing down the swimmer. Swimmers create a laminar flow, which is the opposite of turbulent flow, by covering or removing all their body hair. This allows them to move faster through the water.