Lose (...and gain) weight easily....
Being a passenger in a lift is an easy way to lose (...and, sadly, gain) weight.
If you stand on a set of scales in a lift while it is accelerating downwards, your weight will decrease
Why?
Reveal

Why?
If we consider the system to be just you, the passenger, then the only forces acting on you while the lift is accelerating downwards are
(i) the force the earth exerts on you (what we normally refer to as your weight)
(ii) the normal contact force on you from the scales (acting upwards).
There must be a net downward force when we resolve these two forces, so mg-N=ma, where m is your mass (which of course never changes in this experiment!) and N is the normal contact force on you from the scales (which is what we read as our apparent weight). mg must be greater than N in this case and you appear to have lost weight.
There are lots of demonstrations of this online: here’s one. This video illustrates the point nicely and also shows that once the lift has reaches it cruising speed, your ’wieght’ returns to normal.