lecture7 - Newtons Laws (II) Newtons Free-body diagrams...

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Newton’s Laws (II) Newton’s Laws (II) Free-body diagrams Normal Force Friction, ropes and pulleys Serway and Jewett : 5.7, 5.8
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Free-Body Diagrams Pick one object (the “body”). Draw all external forces which act directly on that body (gravity, contact, electromagnetic). Imagine cutting around the body to separate it from its surroundings. Replace each external object with a force applied at the point of contact. Indicate the direction of the acceleration of the object beside the diagram; but remember, m a is not a force on the diagram.
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Example: free-body diagram A block is pulled up a frictionless ramp: m Note : title, to indicate the chosen object (use m or m A etc) contact forces, to replace the rope and the ramp • gravity doesn’t require contact a may be indicated for reference, but is not a force g m T F n a Forces on Block
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Ropes and Pulleys Tension is uniform in a rope of negligible mass The tension is not changed if the rope passes over an ideal pulley (frictionless and massless) Tension has units of force (newtons) A rope attached to something exerts a force parallel to the rope The magnitude of the force is called the tension in the rope rope Force
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lecture7 - Newtons Laws (II) Newtons Free-body diagrams...

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