WEIGHT AND MASS ARE NOT THE SAME THING,  WEIGHT IS A FORCE (it has a size an a direction),  MASS IS INERTIA A Scalar.

Is it possible for such a small child to lift such a heavy object.  The short answer is no, but the right answer is yes......... sort of.  The answers lies in the difference between weight and mass.  For the child to lift such a large weight he would have to exert a force equal to greater to move it; while to move a large mass is certainly possible, it would just move it a very slow rate.  What to difference? Weight is a force and we have to overcome that force to get it to move, while mass is a resistance to change, but not the prevention of change, massive object will have less change, less massive object will have a greater change, but the motion of the object will change. 

       Weight: If you can finally accept the concept mass even if we have been unable to define it, weight is easy: The weight of a mass is the force that the earth pulls on the mass. We hope you have a feeling for what force means. The entire idea of weight can be understood as the force of gravity on something. Usually we spend most of our time on Earth so our weight is the force that the earth pulls on us. If we get further away from the earth, the force the earth pulls on us is less and we weigh less. If you lived on Mars, the above definition would probably change to: "The weight of a mass is the force that Mars pulls on the mass." The whole idea of weight is related to the force of gravity (and we hate just to use the word "gravity" since it can bring up even more confusion). It would be correct to say, no matter where you might be in the universe that "the weight of a mass is the force of gravity on the mass." In the metric system force is measured in newtons hence weight is also measured in newtons. You will learn later that on the surface of the earth, a mass of 1 kilogram weighs 9.8 newtons. (You will probably never learn anywhere that on the surface of the earth, one slug weighs 32.2 pounds--don't worry about it, very few people know this!) The pound is the US unit of force hence the US unit of weight is also the pound. We will use newtons for the unit of force (and weight) almost always in the discussions that follow.

Definition provided by UCLA