Which force acts perpendicular to a surface in contact and is responsible for supporting the weight component perpendicular to the plane?

Which force acts perpendicular to a surface in contact and is responsible for supporting the weight component perpendicular to the plane?

• A. Normal force
• B. Weight component along the plane
• C. Kinetic friction
• D. Applied force along the plane

Answer: (A)

The normal force is the contact force from the surface that acts perpendicular to that surface. It arises when an object sits on or presses against a surface and prevents it from moving into the surface. On an incline, gravity pulls downward. If you resolve that weight into components relative to the plane, you get a component pressing into the plane (mg cos theta) and a component pulling parallel to the plane (mg sin theta). The normal force adjusts in magnitude to exactly balance the perpendicular component of gravity, so there’s no acceleration into the surface. That perpendicular support is what keeps the object from sinking, and its magnitude is N = mg cos theta (assuming no other perpendicular forces). The other options act along the plane, either as the downslope component of weight or as friction or an applied force parallel to the plane, so they don’t provide the perpendicular support.

The normal force is the contact force from the surface that acts perpendicular to that surface. It arises when an object sits on or presses against a surface and prevents it from moving into the surface.

On an incline, gravity pulls downward. If you resolve that weight into components relative to the plane, you get a component pressing into the plane (mg cos theta) and a component pulling parallel to the plane (mg sin theta). The normal force adjusts in magnitude to exactly balance the perpendicular component of gravity, so there’s no acceleration into the surface. That perpendicular support is what keeps the object from sinking, and its magnitude is N = mg cos theta (assuming no other perpendicular forces).

The other options act along the plane, either as the downslope component of weight or as friction or an applied force parallel to the plane, so they don’t provide the perpendicular support.