If the mass of a body suddenly decreases, would it jump due to normal reaction? Suppose the body of mass M is on a frictionless table, assume g to be the gravitational acceleration. Assume mass of the body changes suddenly(by m)
I was thinking since the mass changes suddenly, the normal reaction would be Mg, while mass of the body would be (M-m)g. Would it cause it to jump?
 A: While we can't actually decrease the mass of an object, we can change the amount of gravity it experiences (more or less).  To do this, imagine your table & mass are in a rocket accelerating through deep space, and the rockets suddenly turn off and leave the whole thing moving at constant velocity.
During the acceleration phase, the mass would need to be accelerated by the table, and would also be exerting a force on the table.  This would cause the top of the table to compress slightly, like a spring.  When the rockets turned off, the rocket (and the table) would stop accelerating. But the table would momentarily stay compressed for a bit longer, meaning that it would still be applying a force to the mass.  This would mean that the table would keep pushing on the mass for a moment after the rockets turned off, causing it to accelerate for slightly more time than the rocket was acceleration.  If we were on the rocket we would feel a gravity-like force holding us "down" in our chairs until the rockets turned off;  and when the rockets turned off, we would see the block rise "up" from the table.
A: Not really different to a compressed vertical spring (compressed table) with a pile of discs on top of it (object) in equilibrium (upward force on discs due to the spring equal to the downward force on the discs due to attraction of Earth) and then some of the discs are rapidly removed by pushing some of them to one side at which time the upward force on the remaining discs due to the spring (same as before) is greater than the downward force on the remaining discs due to attraction of Earth smaller than before).
