Engineering mechanics is a branch of engineering that studies motion and the forces acting on objects. It is a fundamental subject and forms the basis of many other engineering disciplines. Length, time, mass, and force are some basic concepts in engineering mechanics.

Length, which measures the distance traveled by an object, is a fundamental concept in engineering mechanics. We use coordinates relative to a reference point to describe the distance. Length not only helps to describe the distance traveled by an object but it is also used to describe the geometrical properties of physical systems.

For example, consider a bus traveling from city X to city Y. The location of the bus at any given time can be traced with the help of a coordinate system.

In this case, length is insufficient to describe the event, and as a result, time is used to measure the succession of an event, like the traveling time between city X and city Y. Time, which measures the succession of an event, is another fundamental concept in engineering mechanics.

Mass is a measure of the quantity of matter in an object and does not change with location. The mass can be measured by determining the extent to which an object resists a change in its direction or speed when a force is applied.

Force is another important concept in engineering mechanics, defined as the action of one body on another. Forces can either push, pull, attract, or repel one object to another. Gravity is a classic example of a force that attracts objects toward each other.

Pushing an object is an example of using contact force, while an iron piece attracted to a magnet is an example of using non-contact force.

Engineering mechanics relies on certain assumptions to make theoretical analysis possible. Firstly, an object is often treated as a particle with mass whose size can be neglected. This simplification allows us to describe the object's motion using simpler mathematical equations. Secondly, regardless of its material and the load applied, the particle is considered a rigid body, and the deformation is neglected. Finally, the applied load is represented as a concentrated force acting at a point on an object. For example, it is considered a particle when analyzing the load-carrying capacity of a crane hook, irrespective of its size and shape. The hook is a non-deformable body, and a force acts only on a particular point on the hook.