What is the effect of friction on moving objects?

Friction is a force that opposes the motion of an object. When an object is moving, friction acts in the opposite direction to its motion. As a result, friction tends to slow down the object rather than speed it up or have no effect. This is why the correct answer is that friction slows moving objects down.

In practical terms, when a car moves along the road, the tires experience friction with the surface, which allows the car to grip the road but also causes the vehicle to lose speed if additional force is not applied (like pressing the accelerator). Moreover, if an object is sliding on a surface, friction will gradually reduce its speed until it eventually comes to a stop, demonstrating how vital this force is in affecting the motion of objects.