Contact force意思
"Contact force" is a term used in physics to describe a force that arises when two objects are in direct physical contact with each other. This force can be either attractive or repulsive, depending on the nature of the interaction between the two objects. Contact forces are typically classified into two main types:
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Normal force (FN): This is the force that acts perpendicular to the surface of contact between two objects. The normal force is what prevents objects from being crushed or squashed when they are resting on a surface. For example, when you stand on the ground, the Earth exerts an upward normal force on your feet that is equal to your weight (mg), and this force prevents you from sinking into the ground.
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Frictional force (Ff): This is the force that opposes the motion or tendency of motion between two surfaces that are in contact with each other. Friction can be static (when the surfaces are not moving relative to each other) or kinetic (when the surfaces are sliding against each other). The frictional force depends on the nature of the surfaces and the normal force between them. For instance, when you try to push a heavy box across the floor, the frictional force between the box and the floor resists your effort.
Contact forces are often considered in the context of Newton's laws of motion, particularly when analyzing the forces acting on objects in static equilibrium or in motion. They are an important aspect of mechanics, especially in the study of rigid bodies and their interactions.