# Mechanics: Forces and Newtons Laws Ch 4 and Ch 5 in the text…..

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Mechanics: Forces and Newtons Laws Ch 4 and Ch 5 in the text…..

Mechanics Ch4 Ch4 Identifying forces & types of forces Identifying forces & types of forces Forces exist in pairs Forces exist in pairs Contact forces: push, pull, tension, Normal, Friction, Drag (resistant force of fluid), thrust (like a jet engine) Contact forces: push, pull, tension, Normal, Friction, Drag (resistant force of fluid), thrust (like a jet engine) Non-contact forces: gravity, magnetic, electric Non-contact forces: gravity, magnetic, electric

Mechanics Identifying forces and Free Body Diagrams Identifying forces and Free Body Diagrams Draw all forces acting ON the object Draw all forces acting ON the object To aid with this, draw a circle around the object and look at all the forces where the environment touches the system. To aid with this, draw a circle around the object and look at all the forces where the environment touches the system. Dont forget the long range or non-contact forces. Dont forget the long range or non-contact forces. FBDs typically show the object as a dot and the forces are arrows pointing away from the dot. FBDs typically show the object as a dot and the forces are arrows pointing away from the dot.

Mechanics Ch 5 : Newtons 2 nd Law and motion along a line Ch 5 : Newtons 2 nd Law and motion along a line Static equilibrium. F net = 0 in both directions Static equilibrium. F net = 0 in both directions Dynamic problems (w/ acceleration) then a = F net /m, (this is required for all directions with acceleration) Dynamic problems (w/ acceleration) then a = F net /m, (this is required for all directions with acceleration)

Mechanics Friction Friction Kinetic Friction F f = u k Fn (when an object is sliding this is an equals sign. Kinetic Friction F f = u k Fn (when an object is sliding this is an equals sign. Static Friction Ff u s Fn (this is an equals sign right when the object is about to break free) Static Friction Ff u s Fn (this is an equals sign right when the object is about to break free) In general, u s >u k where u = coefficient of friction which is a property of the materials involved. In general, u s >u k where u = coefficient of friction which is a property of the materials involved.

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