Buoyancy and Floating Cups

In this demonstration, cups containing different amounts of water are floated in tap water and in concentrated salt solution to investigate how the volume of displaced liquid relates to the upthrust experienced by the cups. The experiment allows students to compare buoyancy in liquids of different densities.

1. Fill one large container with tap water and another with concentrated salt solution.
2. Place an empty lightweight plastic cup gently on the surface of the tap water.
3. Gradually add water into the cup, observing how much of the cup becomes submerged.
4. Record the volume of water added when the cup reaches a certain depth.
5. Repeat the same process with the cup floating in the salt solution.
6. Compare the depth of submersion and the amount of displaced liquid between the two liquids.
7. Plot graphs of volume displaced versus mass added to analyze the relationship.

📄 Floating Cups - isaac: https://isaacscience.org/questions/itsp_exp_floating

• Use liquids of different densities (e.g., oil, sugar solution) to compare results.
• Try different shapes and sizes of floating containers.

• Ensure containers are stable to prevent spills.
• Wipe up any spilled water or salt solution immediately to avoid slips.

• What determines whether an object floats or sinks? (Whether its average density is less than or greater than the density of the liquid.)
• How is the upthrust force related to the weight of liquid displaced? (They are equal when the object is floating.)
• Why does the cup float higher in salt water compared to tap water? (Because salt water has a greater density, so less volume needs to be displaced to balance the object’s weight.)
• What would happen if the cup were filled with too much water? (It would sink once its weight exceeds the maximum upthrust force possible.)