⚠Tell me Now if u can:- It is said that mass is fixed of an object whether we goes on any planet.
So a person is having a weight of 129 kg and after five weeks his weight get reduced to 79kg.( as we say in daily life).....
And in science weight is in Newton so how the person weight got changed? Is there also change in his mass? Is 9.8m/s² also have some important role here?
(Need an answer which is in both science and daily life reasonable. No FALTU things and people can also give their answer in comment section if they does not get the chance to answer cause i WANT to know THIS!!)
Answers
Mass is the measure of amount of substance with which a body is made of.
Weight is the gravitational pull on the body cz of mass.
So it's obvious that amount of substance with which a body is made does not changes anywhere in universe(unless you consider relativity).
But different celestial objects have different gravitational pull. So force with which a body is pulled also changes. Hence, weight changes according to 'acceleration due to gravity' of a planet.
Value of 'g' on earth changes according to height or depth. To get precision while measuring anywhere on, we gotta make that value independent of 'change in g'. Hence, we use unit of Kg-f(another unit of weight) in daily life.
It is defined as 'equal to the magnitude of the force exerted on one kilogram of mass in a 9.80665 m/s² gravitational field'. So here you can see g is fixed at 9.8 for Kg-f and hence it can be precise at any height or depth.
1 Kg-f = 9.8N
In the case above, His weight is 129 Kg-f in real but we say
129 Kg for ease. So whats his actual weight in SI. It's 129 Kg-f ×9.8
And now F= mg. So weight can change cz of change in mass or change in value of g.
For one week, if he have worked out and got slim, then his mass changed hence weight also changed.
Otherwise he may have gone to heights or depths or ET so that value of g changes and hence his weight changed.
More doubts regarding this in comments is welcome.