lecture4 - acting like a spring (or many springs side by...

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Lecture 4 Applications of Newton’s 2nd Law 1 Review from Last Time Newton’s First Law (Law of Inertia) Newton’s Second Law (The Momentum Principle) 2 Problem Solving - Examples Newton’s second law can be applied in many di±erent situations and that is why it is so important. Isn’t it amazing that the same general equation ( v F = mva ) can be used to solve for the motion of a spring and for a rock falling under the in²uence of gravity! In order to solve problems, we ³rst need to identify the forces acting. Gravity Near Earth’s surface, the acceleration due to gravity is constant ( g =9.81 m/s 2 ) and the force on an object is given by v F = - mg ˆ y . Shoot the monkey DEMO and EXAMPLE emphasize - vertical and horizontal motions are independent. Other forces Tension - acts along a string Normal force - always perpendicular to surface - we can think of the surface as
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Unformatted text preview: acting like a spring (or many springs side by side) that’s compressed and pushes back. DRAW – springs - Hook’s law tell us that the force is proportional to the amount of compres-sion or stretch (will discuss springs more later this week). • Free-Body Diagrams – In Newton’s second law it is the net force that matters! – Therefore, the ³rst step in solving a problem is to identify all the forces acting on each object in the problem. – Free body diagrams provide a handy way of keeping track of an visualizing all these forces. – Note that you must draw a separate free-body diagram for each object in the prob-lem!! – Once you’ve identi³ed all the forces, you can write down Newton’s 2nd law for each component (e.g horizontal, vertical) including all the forces in your diagram. 15...
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This note was uploaded on 05/01/2008 for the course PHYS 13 taught by Professor Millan during the Spring '08 term at Dartmouth.

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