What is the relationship between the formula for net force and formula for weight?

Answer 1

Here is a riddle. Usually if one asks our weight we say, " I'm sixty kg."
Actually our mass is 60 kg. But our weight is the force with which the earth attracts us towards its centre. To get that, we use the formula W = Mg. Here M is the mass of our body ie 60 kg and g is acceleration due to gravity. If suppose we take the value of g as 9.8 m/s^2, then our weight will be 588 N.
Now question arises. Why do we simply say the mass instead weight? Is that a wrong answer?
No, it is not a wrong answer. It's absolutely correct. How?
Actually there is another unit for the force of attraction exerted on a body by the earth's pull. That is kg weight. Usually newton is the unit of force in SI system. But kg wt is also another convenient unit that can be used. One kg wt equals to 9.8 N. This is because the weight of 1 kg body is 1 x 9.8 = 9.8 N. (Recall formula W = Mg)

So when one asks, " What is your weight?", we simply answer as "I'm sixty kg (weight). Thus it is understood as the word 'weight' is in the question itself.
So interesting!
Net force is the resultant of all the forces acting at a point. If a small lead ball is moving down in a jar containing caster oil, then many forces are acting on the ball. One is its weight downwards. Then a buoyant force which equals to the weight of the displaced liquid, which is always upwards. One more force comes into play as the ball moves inside the liquid medium. That force is known as viscous dragging force. This is always opposite to the direction of the movement of the ball inside the liquid.
Hence we calculate the resultant of all these three forces and this is known as net force.