Hooked on Science: Milk Bubbles

Materials

• Two transparent glasses
• Skim milk
• Whole milk
• Two straws
• Ruler

Instructions

• STEP 1: Fill one of the transparent glasses one-fourth of the way with skim milk. Fill the other glass one-fourth of the way with whole milk. Is the milk a solid or a liquid, and why? Describe the milk in each glass by using its observable properties.
• STEP 2: Place a straw in each glass. At the same time, have a friend blow through the straw into one of the glasses of milk, while you blow through a straw into the other glass of milk and observe.
• STEP 3: Using a ruler, measure the height of the pile of bubbles produced from blowing through the straw into each glass. Which type of milk produced the tallest pile of bubbles? Using these measurements, describe the differences between the skim milk and the whole milk. Which milk would be better for creating a cappuccino, and why?

Explanation

The protein in the milk allows the bubbles to form a strong skin. While the whole milk creates some bubbles, the skim milk creates more bubbles. The reason is the fat in the whole milk interacts with the proteins, which weakens the skin of the bubbles, allowing the bubbles to pop faster.