When a person pushes a box across the floor, he is exerting force on the box. The same is true if he lifts the box, drags the box or hits it with a stick. In all cases, he is applying force to the box.
In physics, force is defined as any external application of energy that changes something about the location, direction, velocity or condition of an object. An external force can come from a person, a machine or any number of different sources. The formula for calculating force is F = ma, or "force equals mass times acceleration." Acceleration can only be measured in terms of movement, so if the object being influenced remains motionless, the force is technically calculated as zero, no matter how much effort is being expended. Pushing, pulling, lifting and kicking are all examples of an applied force. There are many other kinds of forces, all of which can influence an object. Some forces, such as gravity and magnetism, exert influence from a distance. Others, such as friction and air resistance, normally act in opposition to the motion of an object. The combined interaction of all the forces present determines whether the object moves, falls, remains in place or comes to rest.