force

Any application of energy, either internal or external to a structure; that which initiates, changes, or arrests motion.

The effect one object has on another, such as a pull or push, which causes or tends to cause a change in motion. A force can cause a body at rest to start moving, slow down, stop, increase its speed, or change direction. Forces can result in deformative movements, rotational movements, and translational movement. That is, they can change the shape of an object, cause it to rotate, or move it from one place to another. Therefore, forces include any agency that alters or tends to alter an object's state of rest or uniform motion. Force is measured in newtons and is the product of the mass of an object and its linear acceleration (i.e., force = mass × acceleration). On the basis of this formula, three different types of forces may be identified (see shear force, fast force, endurance force). As a force is a vector quantity, it is defined by both its size or magnitude, and its direction. In diagrams, a force is often represented by an arrow with the length of the arrow indicating the size of the force, the orientation of the shaft indicating the line of application and one of the arrow's ends indicating the point of application of the force. See also compression, tension.

Energy or power; that which originates or arrests motion or other activity.

• electromotive f. — the force that, by reason of differences in potential, causes a flow of electricity from one place to another, giving rise to an electric current.
• moment of f. — the effect of a force exerted on a lever and about a fixed point.
• reserve f. — energy above that required for normal functioning. In the heart it is the power that will take care of the additional circulatory burden imposed by bodily exertion.
• shearing f. — a force exerted perpendicularly to a horizontal surface.
• Van der Waals f's — the relatively weak, short-range forces of attraction existing between atoms and molecules, which results in the attraction of nonpolar organic compounds to each other (hydrophobic bonding).