Final answer:
Less force is needed to keep an object moving than to start it because of the difference between static and kinetic friction, with kinetic friction being weaker than static. Newton's first law of motion explains that without external forces, like friction, an object in motion will not require extra force to continue moving at a constant velocity.
Step-by-step explanation:
The reason less force is needed to keep an object moving than to start it in motion is primarily due to friction. When an object is at rest, static friction — which tends to be stronger than kinetic friction — must be overcome to start moving the object. However, once the object is moving, only kinetic friction, a weaker form of friction, must be overcome to maintain motion at a constant velocity, as per Newton's first law of motion.
Galileo posited that without any form of resistance, such as friction or drag, an object would maintain its state of motion indefinitely. This concept was incorporated into Newton's first law, which suggests that a force is necessary to change an object’s state of motion, whether that's starting it from rest or altering its speed while it's in motion. Therefore, in the absence of external forces, an object in motion would not require any additional force to keep moving at the same speed and direction.
Friction plays a significant role in our everyday experiences with motion. It is the rubbing force that opposes movement and is responsible for an object eventually coming to a stop if no other force is applied to keep it moving. This concept is especially evident in space, where friction is almost negligible, allowing objects to coast indefinitely.