Normal Force

Normal force is the perpendicular component of the force that a surface pushes on an object. For instance, there is a book on the table. The book exerts 7N on the table, then the table will exert 7N back to the book according to the Newton's third law of motion. The normal force in this example is the table exerting the 7N back to the book.

In order to figure out the normal force with a given mass, apply the Newton's second law of motion to find the weight of the object. For example, an object with a 30 kg is rested on the floor. The normal force and the weight of the object must balance, thus the first step is to find the weight of the object. The weight of this object is inline:F=ma>, or 30 X -9.8 = -294 N. And since the normal force is equal to the weight except pointing in the opposite direction, the normal force is 294 N (pointing upward).