Here's one easy way:
-- Hang an object from a scale. Write down its weight in air.
-- Keep the object hanging from the scale, but let it down into water,
or whatever fluid you're interested in.
-- Read the scale again. Write down its weight in the fluid.
-- Dry everything off, clean up the lab, and go to your office with your notebook.
-- In your notebook, turn to the page with that day's observations.
Notice that the object's weight in air was greater than its weight in the fluid.
-- Subtract the weight in fluid from the weight in air.
The difference is the buoyant force on the object when it's in the fluid.
