Final answer:
Static friction responds to the applied force and can vary up to its maximum value, but it's not always at its maximum. Examples include pushing an object with a force less than the maximum static friction or placing an object on an inclined plane where gravity exerts less force than the maximum static friction.
Step-by-step explanation:
The concept at play in the question is static friction, which is an important topic in physics. When we consider static friction, it is critical to understand that static friction can vary up to its maximum value depending on the opposing force but does not necessarily always match it. For instance, if the maximum static friction between two surfaces is calculated to be 40 N, this does not mean that the static frictional force is always at this maximum. Actual static friction can indeed be less than the maximum before an object begins to move.
Example 1
If a push force of 10 N is applied to an object and the maximum static friction is 40 N, the actual static friction force that counters this push will be 10 N, matching the applied force, not the maximum of 40 N. Thus, in this situation, static friction is less than 40 N.
Example 2
Another scenario where the static friction would be less than 40 N is if the object is on an inclined plane, where the component of the gravitational force trying to pull the object down the plane is less than the maximum static friction. If this component is, say, 15 N, then the static friction force opposing this would only be 15 N to prevent the object from sliding down.