Work(A) Force(F) Distance(D)

Unlike in everyday life, the term «mechanical work» in physics is associated with the displacement of a body under the action of an applied force. Examples of work: a child pulling a toy car with a string, a dropped object falling to the ground, a loader carrying items.

The direction of movement cannot be perpendicular to the action of the force. A book lying on a table exerts a force on it perpendicularly equal to its weight. But the table remains stationary, so the work is zero.

If an object moves in the direction of the applied force, positive work is done. Its magnitude equals the product of the force and the distance over which the body has moved.
A = F x D, where:
A — work;
F — force acting on the body;
D — distance over which the body moved under the action of the applied force F;

Example of positive work: a locomotive pulling wagons.
[A] = 1 J = 1 N x m

If the displacement is opposite to the force, negative work is done.
In this case A = - F x D.
For example, when launching a kite, the gravitational force does — negative work.

If the magnitude of the applied force is not constant or directed at an angle to the direction of the body's movement, the work is calculated using other, more complex formulas.

Total work is defined as the sum of the work of all forces acting on an object. Depending on the magnitude of the work and the time taken to perform it, the necessary power of machines and mechanisms and fuel consumption are determined.