# Will frictional force work against the vertical direction of velocity of an object?

We assume that an object is placed on a horizontal plane. If this object is accelerated to vertical direction, will frictional force act against the vertical direction of velocity of object? For any kind of applied force, will frictional force work against the vertical direction of velocity of an object?

– user36790
Jan 24, 2015 at 17:42

In physics, the normal force is always perpendicular to the surface of contact between two bodies. And when there is friction, the force of friction is always, by definition, perpendicular to the normal force. The magnitude of the friction force is also proportional to the magnitude of the normal force, and the constant of proportionality is denoted as $\mu$.