Describe the factors that cause static friction between two surfaces to increase

Let's consider an object on a horizontal surface. The magnitude of the frictional (static) force is given by:

where m is the mass of the object, g is the gravitational acceleration, and \mu is the coefficient of static friction.

Looking at the formula, we see that there are mainly two factors that affect the magnitude of the frictional force:
- the mass of the object: m. The greater its mass, the larger the frictional force
- the coefficient of friction, . This coefficient becomes larger when the roughness of the two surfaces increases.

So, we can summarize the answer as follows: the factors that cause static friction to increase are the mass of the object on the surface and the roughness of the two surfaces.