In the case of static friction, if the downward force between the surfaces is doubled, the friction will:

Static friction is the force that resists the initiation of sliding motion between two surfaces in contact. The maximum static frictional force can be calculated using the formula:

F_friction = μ_s * N

where F_friction is the frictional force, μ_s is the coefficient of static friction, and N is the normal force (the downward force between the surfaces).

When the downward force (normal force) is doubled, it directly affects the frictional force. Since static friction is directly proportional to the normal force, if the normal force is increased, the maximum possible static frictional force will also increase correspondingly. Therefore, if the downward force is doubled, the frictional force will also double, hence increasing by twice as much.

This relationship highlights the dependence of static friction on the normal force, confirming that as the surfaces are pressed together with greater force, the frictional force that resists motion also increases proportionately.