Here's why:
* Static Friction: When an object is at rest, there's a force called static friction acting against any force trying to move it. This force is directly proportional to the normal force pressing the object against the surface, and the coefficient of static friction between the surfaces. The higher the coefficient, the harder it is to overcome static friction.
* Overcoming Static Friction: To get an object moving, you need to apply a force greater than the maximum static friction force. Once the object starts moving, the friction changes to kinetic friction.
* Kinetic Friction: Once the object is moving, the friction acting on it is called kinetic friction. It's typically less than static friction.
Example: Think about pushing a heavy box across a floor. It's harder to get the box moving (overcoming static friction) than it is to keep it moving once it's going (kinetic friction).
