The forces whose line of action lie along the same line are known as:
collinear forces
Understanding Forces and Their Lines of Action
In the study of mechanics, forces are often classified based on their arrangement in space and relative to each other. A key concept is the line of action of a force, which is the infinite straight line along which the force acts.
The question asks about forces whose lines of action lie along the same line. Let's examine the options provided to identify the correct classification.
Analyzing Force Classifications
Here's a breakdown of the different types of force systems mentioned in the options:
- Collinear Forces: These are forces whose lines of action lie along the same straight line. They can act in the same direction or opposite directions along this common line.
- Coplanar Forces: These are forces whose lines of action all lie in the same plane.
- Concurrent Forces: These are forces whose lines of action all intersect at a single point. This point may or may not lie within the body on which the forces are acting.
- Parallel Forces: These are forces whose lines of action are parallel to each other. They can be in the same plane (coplanar parallel) or in different planes (non-coplanar parallel).
Evaluating the Options
Now let's relate these definitions back to the options:
- Coplanar parallel forces: These are forces in the same plane with parallel lines of action. Their lines of action do not necessarily lie on the same line; they are distinct parallel lines within the plane.
- Collinear forces: These are forces whose lines of action lie along the same straight line. This directly matches the description given in the question.
- Coplanar concurrent forces: These are forces in the same plane whose lines of action intersect at a single point. While they are in the same plane, their lines of action typically do not lie on the same single line (unless all forces are acting towards or away from the point of intersection and are collinear through that point, which is a special case). The general definition is intersection at a point, not lying on the same line.
- Coplanar non-concurrent forces: These are forces in the same plane whose lines of action do not all intersect at a single point. This category includes coplanar parallel forces (where lines are parallel but distinct) and other systems where lines intersect at multiple points or are neither parallel nor concurrent. Their lines of action do not lie along the same single line.
Conclusion on Forces with Lines of Action Along the Same Line
Based on the definitions, the term that specifically describes forces whose line of action lie along the same line is collinear forces. This is regardless of whether they are in the same plane or not, or if they are concurrent (though forces concurrent on a line are collinear) or parallel (parallel forces on the same line are collinear).
Therefore, the forces whose line of action lie along the same line are known as collinear forces.
| Classification | Description |
|---|---|
| Collinear Forces | Lines of action lie along the same single line. |
| Coplanar Forces | Lines of action lie in the same plane. |
| Concurrent Forces | Lines of action intersect at a single point. |
| Parallel Forces | Lines of action are parallel to each other. |
| Coplanar Parallel Forces | In the same plane, lines of action are parallel (and usually distinct). |
| Coplanar Concurrent Forces | In the same plane, lines of action intersect at a single point. |
| Coplanar Non-concurrent Forces | In the same plane, lines of action do not all intersect at a single point. |
Revision Table: Key Definitions for Force Systems
| Term | Meaning |
|---|---|
| Line of Action | The infinite line along which a force vector lies. |
| Collinear | Lying on the same straight line. |
| Coplanar | Lying in the same plane. |
| Concurrent | Meeting at a single point. |
| Parallel | Having lines of action that are parallel. |
Additional Information on Types of Force Systems
Force systems can be broadly classified based on the spatial arrangement of the forces:
- Two-Dimensional (2D) Systems: All forces lie in a single plane (coplanar). These can be further classified as:
- Coplanar Concurrent: Lines of action meet at one point.
- Coplanar Parallel: Lines of action are parallel.
- Coplanar General (Non-concurrent, Non-parallel): Lines of action are in the same plane but neither all concurrent nor all parallel.
- Three-Dimensional (3D) Systems: Forces do not all lie in a single plane (non-coplanar or spatial). These can be:
- Spatial Concurrent: Lines of action meet at one point in space.
- Spatial Parallel: Lines of action are parallel in space.
- Spatial General: Forces are not all in the same plane, and their lines of action are neither all concurrent nor all parallel.
Collinear forces are a special case. If they are in the same plane, they are also coplanar. If they act through a common point on the line, they are also concurrent (on that point). The defining characteristic of collinear forces is that their lines of action share the exact same single line.
Important Questions from Equilibrium and Friction
How does a lubricant reduce friction between moving parts of a machine?
The necessary condition of equilibrium of a body is-
The forces which meet at one point and have their line of action in different planes are called
If in a planar system, only 2 reaction forces are acting, then the system is:-
By applying the static equations i.e. ∑H = 0, ∑V = 0 and ∑M = 0. To a determine structure, we may determine:
