why does a wadded up foil sink
http://www.newton.dep.anl.gov/askasci/gen06/gen06769.htm
Metal foils such as aluminum have a higher density than water. By "wadding it up" you prevent there being any empty volumes inside to give it buoyancy. The denser material (the foil) sinks to the bottom.
A wadded up foil sinks because the density of the foil is greater than the density of water. When an object is placed in a fluid, it will either sink or float depending on its density relative to the density of the fluid.
Here's how you can understand this phenomenon:
1. Density: Density is a measure of how much mass is contained in a given volume of a substance. The density of an object is calculated by dividing its mass by its volume. Objects that have a higher mass per unit volume are denser than those with lower mass per unit volume.
2. Archimedes' Principle: Archimedes' principle states that the buoyant force acting on an object submerged in a fluid is equal to the weight of the fluid displaced by the object. If the buoyant force is greater than the weight of the object, it will float. If the buoyant force is less than the weight of the object, it will sink.
3. Foil and Water: Aluminum foil has a higher density than water, which means that its mass per unit volume is higher than that of water. When you wad up foil and drop it in water, it displaces a small volume of water. Since the foil's density is greater than that of water, the weight of the water it displaces is less than its own weight. As a result, the buoyant force on the foil is less than its weight, causing it to sink.
So, the wadded up foil sinks because its density is greater than the density of water, and the buoyant force acting on the foil is not enough to overcome its weight.