What Is Force?

Posted on 27 Jan 2012 22:05

Blog Home

More on Biomechanics

Training for maximal strength is essentially training to exert maximum muscular force. So what is force? The easiest way to think of a force is as a simple push or pull. When you push or pull on a barbell or other implement you are exerting a force. The pull of the Earth's gravity on an object is a force. Friction is a force. To be more precise, then, a force is something that causes or tends to cause a change in the motion or the shape of an object.

When you attempt to deadlift a heavy barbell you are exerting a pulling force on the barbell. That force has a magnitude, a direction, and a point of application. By applying the force you are attempting to change the state of motion of the barbell. If your force is too weak, the barbell will not move. There is a greater force acting against your effort. In this case it is the weight of the barbell or the inertia of the barbell. The weight is the downward force of the Earth's gravity acting on the weight, which is proportional to its mass. The inertia of the object is its tendency to maintain its state of motion, whether moving or not. Inertia is easy to understand. The more massive an object is the more it tends to maintain its present state of motion. A 300 lb barbell has a lot of inertia. Now imagine a 300 lb linebacker running at you full-tilt. To stop him, you'd have to overcome his inertia. In either case, you must change the state of motion the object or body.

The failure to move a heavy weighted implement, such as our barbell, is a source of confusion for strength trainees. This is because the application of force is thought of as the actual result of the force or more specifically, its effect. Most strength training articles concerning force simply relate the classic Newtonian law F = ma which translates to force equals mass times acceleration where m is the mass of an object in grams or kilograms, and a is the amount of change in velocity in meters per second squared, i.e. acceleration. However, although this is usually reported as the absolute definition of force it is really a relationship or a means to measure the effect of force which is the resultant acceleration of an object. This is great for physics and mechanical laws but for defining force it makes force itself a mere abstraction that grows out of the change of an object's velocity. This view of force, despite its precision, doesn't really help us train for strength as the effort we exert against a weight is NOT an abstraction.

Even if your barbell does not move your application of force to it creates a tendency for it to move. If a friend also grabbed on to lend a hand, the barbell might move. The absolute force being applied to the bar increases. Our goal, then, in training for maximal strength is to increase our ability to exert muscular force, plain and simple. Force is probably mentioned on GUS more than any other strength related word. For further reading see the many other pages concerning force or forces.

Some Technical Notes, Just for Fun

• The symbol for force is F.
• The pound is a unit of force. However, the SI unit1 of force is the Newton, named after Isaac Newton and abbreviated as N.
• A newton of force is the force required to accelerate a 1 kg mass 1 m/s/s which is written in mathematical terms as: 1.0 N = (1.0 kg)(1.0 m/s/s). One newton equals 0.225 lb of force and one pound equals 4.448 N.
• Force must be considered in terms of its point of application, its direction or "line of action", and whether is pushes or pulls. Since a force has magnitude (size) and direction it is a type of vector. A vector is represented by an arrow on a free body diagram. The length of the arrow represents the size of the vector, the orientation represents direction, and one end of the arrow represents its point of application. Other vector quantities are weight, pressure and torque.
• For the purposes of strength training we are not concerned with a force that deforms, or changes the shape, of another object. Instead, we are concerned with forces that either start, stop, speed up, slow down, or change the direction of an object. Since deformation is ignored or assumed not to occur this is called rigid-body mechanics.