Statics

Torsion

when you twist an object

Moment Couple

A couple is defined as two parallel forces that have the same magnitude, but opposite directions, and are separated by a perpendicular distance d, Fig. 4-25. Since the resultant force is zero, the only effect of a couple is to produce an actual rotation, or if no movement is possible, there is a tendency of rotation in a specified direction.

Force

A force represents the action of one body on another. It is generally characterized by its point of application, its magnitude, and its direction. Forces acting on a given particle, however, have the same point of application

External forces

External forces are exerted by other bodies on the rigid body under consideration. They are entirely responsible for the external behavior of the rigid body, either causing it to move or ensuring that it remains at rest.

magnitude

Greatness of size, strength, or importance

Rectangular Components of a Force: Unit Vectors

In many problems, it is useful to resolve a force into two components that are perpendicular to each other. Figure 2.14 shows a force F resolved into a component Fx along the x axis and a component Fy along the y axis. The parallelogram drawn to obtain the two components is a rectangle, and Fx and Fy are called rectangular components. The x and y axes are usually chosen to be horizontal and vertical, respectively, as in Fig. 2.14; they may, however, be chosen in any two perpendicular directions, as shown in Fig. 2.15. In determining the rectangular components of a force, you should think of the construction lines shown in Figs. 2.14 and 2.15 as being parallel to the x and y axes, rather than perpendicular to these axes. This practice will help avoid mistakes in determining oblique components

Internal forces

Internal forces hold together the particles forming the rigid body. If the rigid body is structurally composed of several parts, the forces holding the component parts together are also defined as internal forces.

Resultant force

Net force, also known as resultant force, is a vector quantity produced when two or more forces act upon one object. The concept of net force is the same as the mathematical concept of vector addition.

Moment

The Moment of a force is a measure of its tendency to cause a body to rotate about a specific point or axis. This is different from the tendency for a body to move, or translate, in the direction of the force. In order for a moment to develop, the force must act upon the body in such a manner that the body would begin to twist. This occurs every time a force is applied so that it does not pass through the centroid of the body. A moment is due to a force not having an equal and opposite force directly along it's line of action.

Line of action (of a force)

The line of action is the infinite straight line along which the force acts; it is characterized by the angle it forms with some fixed axis.

Moment Arm

The moment arm or lever arm is the perpendicular distance between the line of action of the force and the center of moments. Also known as Torque or Lever

point of application

The point of application is the exact location at which a force is applied to a body. This point is usually described by a set of coordinates and is represented graphically by the tip of the arrowhead.

direction of a force (The Sense)

The sense of a force specifies the direction (positive or negative) in which the force moves along the line of action.

Adding vectors

The sum of the two vectors thus can be found by arranging P and Q in tip-to-tail fashion and then connecting the tail of P with the tip of Q.

tension

When you pull on an object from both ends causing it to stretch

Compression

When you push on an object from both ends causing it to shrink

Shear

When you put a force one up and one down on each end of an object causing it to rip in half