Final answer:
The force needed to move an object up an inclined plane becomes smaller as the plane gets longer, due to a less steep incline. If isolines of gravitational potential get closer, it implies a steeper slope. Constant velocity on an incline is maintained when weight along the slope equals frictional force.
Step-by-step explanation:
As the inclined plane gets longer, the force needed to move the object gets smaller. This is because the longer the plane, the less steep the incline, which means that the component of gravitational force acting parallel to the surface of the plane is reduced. Therefore, less force is required to counteract this component and move the object up the plane.
In the context of gravitational potential, if isolines of gravitational potential get closer together, this indicates a steeper slope. This is analogous to electric potential, where closer isolines indicate a stronger electric field. Similarly, a hill with closer gravitational potential isolines would have a steeper slope because the gravitational field strength would be greater.
When an object is sliding down an inclined plane at a constant velocity, it occurs when the magnitude of the component of the weight along the slope is equal to the magnitude of the frictional force.