Which type of friction is generally higher: static or kinetic?

• A. Kinetic friction is higher than static friction.
• B. Static friction is higher than kinetic friction.
• C. They are always equal.
• D. Friction depends only on velocity.

Answer: (B)

When an object is at rest on a surface, friction acts to prevent motion and can adjust to whatever force is needed, up to a maximum value. That maximum static friction is proportional to the normal force (μsN), and static friction can match the push you apply until you reach the threshold where motion starts. This means static friction can be quite large, resisting the start of sliding.

Once the object starts moving, friction becomes kinetic and is typically smaller than the maximum static friction. The kinetic friction force is μkN, and for most materials μk is less than μs. So the friction encountered during sliding is usually less than the maximum friction that could hold the object at rest. That’s why static friction is generally higher than kinetic friction.

It’s not correct to say friction depends only on velocity, and static friction isn’t always equal to kinetic friction (they’re different depending on whether the object is at rest or sliding).