Looking for a fun, hands-on STEM activity to do with kids over the holidays—or better yet, a memorable party trick? Try the Atomic Motion in a Glass of Water Experiment!
Start with three glasses of water: one filled with ice water, one with room-temperature water, and one with hot tap water. Add 3 drops of food coloring to each glass—but first, ask your audience to predict which one will mix completely first and which will take the longest to mix. What’s your guess?
Scroll down for the answer and science behind it.
Want to take the experiment to the next level? Swap the food coloring for a single Alka-Seltzer tablet in each glass and watch the reactions unfold!
Answer:
The food coloring in the hot water will completely mix first, followed by the room-temperature water, and finally the ice water.
Hot water has higher thermal energy because the water molecules are randomly moving at higher speeds than in cool water. Those faster-moving molecules mix the food coloring more quickly. In contrast, the slower-moving molecules in colder water (like ice water) need more time to defuse the food coloring. This is also why hot water better dissolves sugar when making sweet tea!
