False

Frictional force is not directly proportional to the surface area of a solid. It depends on several other factors such as the nature of the surfaces in contact, the force pressing the surfaces together, and the roughness of the surfaces.

Factors affecting frictional force:
- Nature of the surfaces: Frictional force depends on the types of surfaces in contact. Smooth surfaces have less friction compared to rough surfaces.
- Normal force: Frictional force is directly proportional to the normal force between the two surfaces. Normal force is the force exerted perpendicular to the surfaces in contact.
- Coefficient of friction: It is a measure of the roughness between the two surfaces. It depends on the materials in contact and affects the frictional force.
- Contact area: While contact area does play a role in determining friction, it does not have a direct proportionality relationship. Frictional force is not solely determined by the surface area of the solid.

Explanation:
Frictional force is the force that opposes the motion or attempted motion of an object. It occurs due to the interaction between the molecules on the surfaces in contact. When an object is placed on a surface, the weight of the object exerts a force perpendicular to the surface called the normal force. Frictional force acts parallel to the surface and opposes motion.

The coefficient of friction determines the magnitude of the frictional force. It depends on the nature of the surfaces in contact and can vary widely. For example, the coefficient of friction between a rough surface and a smooth surface will be higher compared to two smooth surfaces. The roughness of the surfaces affects the coefficient of friction.

The contact area between the surfaces also affects the frictional force. Generally, larger contact areas result in larger frictional forces. However, it is important to note that the relationship between contact area and frictional force is not directly proportional. Increasing the contact area does not always result in a proportional increase in the frictional force.

In conclusion, frictional force is not directly proportional to the surface area of a solid. It depends on various factors such as the nature of the surfaces, normal force, and coefficient of friction.