If you closed your eyes, held out a cup, and asked someone to gently pour water in it, how much liquid would need to be added before you noticed a change in weight? One drop? Probably not.
One ounce? Maybe. The answer is called the discrimination threshold for detecting weight differences. Interestingly enough, it depends on how heavy the cup is. By the way, donít try this experiment in a public place or the change you notice will be the coins at the bottom of your cup and you could get arrested for panhandling.