Slowly Sinking Cupcake Cup

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What type of experiment is this?

Experimental procedure and explanation:

• An aluminum cupcake cup was submerged in water.
• In water, the cupcake cup sinks extremely slowly compared to its speed when falling in air (Slowly Falling Cupcake Cup). The main reason for this is that the density of water is more than 800 times the density of air, and therefore if the cupcake cup were to move at the same speed in both media, the resistance would be more than 800 times higher in water. In fact, the resistance in water acts as a brake and the cupcake cup never reaches the same speed that it reaches when it falls in air. Therefore, the cupcake cup reaches its terminal velocity immediately upon being submerged in water.
• The cupcake cup’s buoyancy in water, which acts in an upward direction, further slows the speed of the cupcake cup as it sinks. Buoyancy from the air also acts on an object falling in air; however, this buoyancy is usually very small compared to the gravity acting on the object, and the buoyancy effect in air can therefore be ignored.
• In this experiment, we are testing the resistance of water; however, the principle is the same as that of air resistance. In fluid dynamics, there is no theoretical difference between air resistance and water resistance. The resistance acting on an object from the flow of the liquid or gas, which is a force that acts in the direction of flow, is called drag.
• If we let go of the cupcake cup at an angle, the flow changes direction at the side of the cupcake cup; however, the change in flow direction induces a force acts to return the cupcake cup to a horizontal orientation, and eventually the cupcake cup sinks.

[Keywords]	Water resistance, Terminal velocity
[Related items]	Slowly Falling Cupcake Cup
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, P136－139. “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P66－69. “Introduction to Fluid Dynamics,” by Ryozo Ishiwata, Morikita Publishing, P123－124.