Consider an object of mass m kg, falling freely under gravity with an acceleration g m/s^2

 

 

 

 

 

 

 

 

 

 

 

We know that the force producing the acceleration is the weight, W newtons, of the object, so using F = ma gives

W = mg   

i.e.       a body of mass m kilograms has a weight of mg newtons.

For example, taking the value of g as 9.8, the weight, W newtons, of a person whose mass is 55 kg is given by

W = mg = 55 x 9.8 = 539 N

If the weight of a rockery stone is 1078 N, its mass, m kg, is given by

    W = mg  => W/g =1078/9.8 = 110

therefore the mass of the stone is 110 kg.

You can get an idea of what a newton is like if you think of the weight of a smallish apple.

WEIGHT