<P> A contact force is any force that requires contact to be enforced . Contact forces are also direct forces . Contact forces are ubiquitous (present, appearing, or found everywhere) and are responsible for most visible interactions between macroscopic (visible to the naked eye; not microscopic) collections of matter . Pushing a car up a hill or kicking a ball or pushing a desk across a room are some of the everyday examples where contact forces are at work . In the first case the force is continuously applied by the person on the car, while in the second case the force is delivered in a short impulse . Certain contact forces describe specific phenomena and are important enough to have been given unique names . The most common instances of this include friction, normal force and shear force . A contact force may also be described as the push experienced when two objects are pressed together . </P> <P> In the Standard Model of modern physics, the four fundamental forces of nature are known to be non-contact forces . The strong and weak interaction primarily deal with forces within atoms, while gravitational effects are only obvious on a macroscopic scale . Molecular and quantum physics show that the electromagnetic force is the fundamental interaction responsible for contact forces . The interaction between macroscopic objects can be roughly described as resulting from the electromagnetic interactions between protons and electrons of the atomic constituents of these objects . Everyday objects do not actually touch; rather, contact forces are result of the interactions of the electrons at or near the surfaces of the objects (exchange force). This includes friction . </P>

Report on contact force and force at a distance