183_notes:friction

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183_notes:friction [2021/02/18 21:20] – [Contact Interactions: The Normal Force & Friction] stumptyl183_notes:friction [2021/02/18 21:23] (current) – [Friction] stumptyl
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 ===== Forces due to contact ===== ===== Forces due to contact =====
  
-When two objects are in contact, their contact surfaces exert forces on each other. This is quite different from the gravitational force because while it acts on every piece of mass, as you will learn, we consider that it acts at the [[http://en.wikipedia.org/wiki/Center_of_mass|center of the of mass]] of the object. This assumption doesn't often affect our predictions and explanations of motion.  In fact, in all the models that you have used so far, we haven't been concerned about exactly where the force acts on an object only that it does act.+When two objects are in contact, their contact surfaces exert forces on each other. This is quite different from the gravitational force because while it acts on every piece of mass, as you will learn,__ //_we consider that it acts at the [[http://en.wikipedia.org/wiki/Center_of_mass|center of the of mass]] of the object.//__ This assumption doesn't often affect our predictions and explanations of motion.  In fact, in all the models that you have used so far, we haven't been concerned about exactly where the force acts on an object only that it does act.
  
 For contact forces, (for a time) you will continue to use the assumption that we can just consider whether a contact force acts or not (And in what direction it acts). In the future, you might need to know precisely where it acts because [[183_notes:pp_vs_real|it might cause the motion to be a bit more complicated]]. For example, you can tip a box over if you push on it at the right location, but below that location it doesn't tip over. For contact forces, (for a time) you will continue to use the assumption that we can just consider whether a contact force acts or not (And in what direction it acts). In the future, you might need to know precisely where it acts because [[183_notes:pp_vs_real|it might cause the motion to be a bit more complicated]]. For example, you can tip a box over if you push on it at the right location, but below that location it doesn't tip over.
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 [{{ 183_notes:mi3e_04-024.png?200|Start pushing a brick on a table and the atoms rearrange a bit; they resist the motion}}] [{{ 183_notes:mi3e_04-024.png?200|Start pushing a brick on a table and the atoms rearrange a bit; they resist the motion}}]
  
-Friction is a resistive force that is due the contact between two objects. While the normal force is perpendicular to the contact surfaces, the frictional force is parallel. So, the vector sum of these two forces (when both are acting) is the force that the surface exerts on the object. That is, both the normal and frictional forces are due to the same contact interactions, they are often just separated into parallel and perpendicular components to the surface for convenience.+Friction is a resistive force that is due the contact between two objects. //While the normal force is perpendicular to the contact surfaces, the frictional force is parallel.// So, the vector sum of these two forces (when both are acting) is the force that the surface exerts on the object. That is, both the normal and frictional forces are due to the same contact interactions, they are often just separated into parallel and perpendicular components to the surface for convenience.
  
 [{{183_notes:asperities.png?200|The roughness of two materials in contact shown at the microscopic level. }}] [{{183_notes:asperities.png?200|The roughness of two materials in contact shown at the microscopic level. }}]
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