Using what you know about friction, explain why it requires much more effort to push an object that is stationary than is does to push an object that is already in motion.

Answer 1

The difference in effort required to push a stationary object versus one that is already in motion can largely be attributed to the concepts of static friction and kinetic friction.

1. Static Friction: When an object is stationary, the force resisting motion is known as static friction. Static friction must be overcome to initiate movement. This force is generally higher than kinetic friction due to the molecular adhesion between the surfaces in contact. Essentially, static friction acts to keep the object at rest and can vary up to a certain maximum value, known as the maximum static friction.

2. Kinetic Friction: Once the object is in motion, the relevant force becomes kinetic friction, which is generally lower than maximum static friction. Kinetic friction is the force that opposes the motion of two surfaces sliding past each other. For most materials, the coefficient of kinetic friction is less than that of static friction, which means it takes less force to maintain movement once it has begun than it does to start moving it in the first place.

Therefore, when you push a stationary object, you must apply enough force to overcome the higher static friction, leading to the greater effort required. Once the object starts to move, you only need to overcome the lower kinetic friction, which is why it feels easier to keep it in motion.

In summary, the greater effort to push a stationary object is due to the higher resistance provided by static friction compared to the resistance offered by kinetic friction when the object is in motion.