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### Student Question

Secondary IV • 2yr.

I do not understand the concept of effective force? Why would a force be ineffective?

Physics

## Explanations (1)

• Explanation from Alloprof

Explanation from Alloprof

This Explanation was submitted by a member of the Alloprof team.

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Team Alloprof • 2yr.

All forces "work", but they are not useful for moving an entire object.

For example, if you press down on a desk vertically, you will hardly be able to move it to one side or the other. However, if you press down on that same desk from one of its sides, you will be able to move it much more easily.

Even though the force applied was the same in both cases, they did not have the same effectiveness. Indeed, almost all of the force applied to the side was used to move the desk while the other force did not move.

In short, we define more formally the effective force as being the part (component) of a force which is directly responsible for the displacement of an object. Trigonometric calculations are used to find the effective component of the forces.

For example, when we know the angle between the displacement and the force, we can multiply the norm of the force by the cosine of this angle in order to find the value of the effective force. A force parallel to the displacement of the same magnitude as the effective force would produce the same effect on the moving object.

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