Increasing the normal force between two surfaces has a direct effect on the static friction force. The relationship between the normal force and static friction can be described by the equation:
Static friction force (Fs) = coefficient of static friction (μs) × normal force (Fn)
According to this equation, the static friction force is directly proportional to the normal force. As the normal force increases, the static friction force increases proportionally.
The normal force is the force exerted by a surface perpendicular to the contact surface. It is equal to the weight of an object when it is on a horizontal surface and opposes the force of gravity. The normal force is influenced by the weight of the object and the perpendicularity of the surface.
By increasing the normal force, you effectively increase the force pressing the two surfaces together. This results in a greater number of asperities in contact and an increase in the interlocking between the surfaces. Consequently, the static friction force needs to increase to balance and prevent relative motion between the surfaces.
For example, consider pushing a heavy box along the floor. If you apply a greater force downward (increasing the normal force), the static friction force between the box and the floor must also increase to match the applied force. This allows the box to resist being set into motion and enables you to exert more force without causing the box to slip.
However, it's important to note that there is a limit to the maximum static friction force, which is determined by the coefficient of static friction. If the applied force exceeds this limit, the object will overcome the static friction and start moving, experiencing kinetic friction instead.