Which is heavier, a ton of feathers or a ton of lead?

They're both the same. The feathers would take up a lot more space though! Feathers have a lower density than lead (i.e. for the same volume, feathers are less heavy). In practice, if you drop a tonne of feathers and a tonne of lead from the same height at the same time (on Earth), the feathers will be pushed around more by air resistance and will take longer to reach the ground. But if you did that experiment somewhere without air resistance (e.g. another planet) you'd see that they would take the same amount of time, because they would have the same weight (and mass).