Unformatted text preview: s. If you are in free‐fall, it may be easy to hold a massive object due to the weightlessness, but it is sWll diﬃcult to shake it due to its inerWa.
If a surface is pushed, it pushes back. Such a force is called a “normal force.” The direcWon of normal force is perpendicular to the surface. If a book is siing on top of a table, the surface of the table exerts a normal force of a magnitude equal to the weight of the book siing on top of it, thus prevenWng it from acceleraWng down to the ground. Normal force Normal force Surfaces in contact can exert forces on each other that are parallel to the contacWng surfaces. A component of a contact force that opposes sliding, or the tendency to slide, is called a fricWonal force. FricWonal force FricWonal force Force exerted by a compressed or stretched spring obey Hooke’s Law. Fx = ! kx
“‐”: the direcWon of force is opposite from the displacement of the end of the spring, “restoring force.” k: “force constant” sWﬀness of the sp...
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