Final answer:
To make a bucket lighter you could humorously add 'a hole' according to the context of a riddle. In actuality, items with mass like rocks, feathers, sand, and water would increase the bucket's weight. Density and mass are different concepts; feathers have a lower density than bricks, so they occupy more space for the same mass.
Step-by-step explanation:
What Can Make a Bucket Lighter?
The riddle asks what you can put in a bucket to make it lighter. The answer is not one that fits with conventional understanding, as adding anything of mass to a bucket would typically make it heavier. However, in the context of a riddle, the clever answer that pairs with the nature of the question would be 'a hole'. The other options given, such as rocks, feathers, sand, and water, all have mass and would make the bucket heavier when added.
Now, to explain the mass versus density concept, a ton of feathers and a ton of bricks have the same mass by definition, since a ton is a measure of mass. However, the density of bricks is much greater than that of feathers, meaning that for the same mass, feathers will take up more space due to their lower density.
In the example of bird bones, their construction with air pockets significantly reduces their average density compared to other animal bones, which, similar to the ton of feathers, allows them to 'weigh less' or be lighter compared to something of a similar size but higher density.