Question

You find your mass to be 42 kg on a weighing machine.is your mass more or less than 42 kg?

Answer 1

Your mass will be lesser than 42 KG, as it is the weight which is displayed on the machine, and weight is mass*gravity, mass multiplied with gravity.

Answer 2

Your mass will be more than 42 kg as when you stand on the machine in the air around you, you will be acted upon  by an upward force due to your force towards gravity as the air surrounding you is also a fluid. So, this is the reason as you experience an upward force thus your real mass will never be calculated by the machine. It will always be lesser than what you weigh.