What is meant by the term mechanics

Amount, direction and point of application of a force

A force is characterized by the amount, the direction and the attackpoint


The amount represents the magnitude of the acting force. The unit of measurement here is N = Newton ($ 1 N = \ frac {kg \; m} {s ^ 2} $). Forces can be of different sizes. Larger weights have greater forces and vice versa. The amount $ F $ of a force can be measured by comparing it with the force of gravity (or with a suitable weight force $ G $). The weight force is the mass in kilograms (kg) multiplied by the acceleration due to gravity $ g = 9.81 \ frac {m} {s ^ 2} $.


Every force has a direction, which determines how a body is loaded. This is how the weight $ G $ (also: $ F_G $) actsalways straight down. However, if I visit a friend and have to press the doorbell, I cannot use the existing gravity because it works in the wrong direction. Therefore, I need a horizontal force, such as the muscle strength of my index finger. This simple example shows that the direction of the force determines how a body is loaded.

The direction of the force can be described by their Line of action and the Sense of direction:

Line of action and sense of direction

In the graphic above, the line of action $ f $ of the force $ F $ can be seen. The Sense of directionthe force $ F $ is given by the arrow. If the force shows neither in the vertical nor in the horizontal direction, the angle $ \ alpha $ of the force to the horizontal is given. It is possible to determine the deviation of the line of action from the horizontal using an angle. In the graphic above, the force $ F $ is applied with the angle $ \ alpha $ to the horizontal in the direction of the arrow in order to hold the weight $ G $.


Finally, the point of attack is described. This indicates the point on a body that is loaded by a force with a certain amount from a certain direction. As soon as the point of attack shifts, the effect on the stressed body also changes. This means that depending on where the point of application is and in which direction the force acts, different movements of the body are the result.

In the above figure, the force $ F $ causes a shift to the top left of the first cube and a shift to the bottom right of the second cube.