Practical physics!

A lady who once taught in an adult education class relates how she had a hard time convincing an elderly man that half a kilo of cotton weighed exactly the same as half a kilo of iron. The man shook his head slowly in disbelief, and she finally gave up when he said to her, “Madam, you go downstairs and stand under the window outside and let me drop a half a kilo of cotton on your head. Then let me drop a half a kilo of iron on your head. And then tell me which one is heavier.”