Physics October--20-08

# Physics October--20-08 - motion into small enough...

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Physics October-20-08 You do positive work if your displacement is in the same direction as the work done. Regular Work: W=F d cosØ Work done by a spring is a bit more complicated. A relaxed spring is when it is neither compressed nor stretched. When you stretch a spring horizontally, it wants to pull back to equilibrium. Similarly when you stretch a spring vertically, it wants to return to equilibrium. A spring force is not a constant force. The further you stretch it, the greater the force increases. Hooke’s law deals with a mass less, idea spring and it states: F = -k d In one dimension, k is called the spring constant. This is the stiffness of the spring and has the units N/m. Hooke’s Law is a variable force. The magnitude of the force is not a constant, so we have to divide the

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Unformatted text preview: motion into small enough segments (Δx) that we can take the force to be constant in each. Work done by a spring: W s = ∑ΔW i = ∑FΔ x =-k∑ x j Δ x OR W = Xf ∫ xi F dx = Xf ∫ xi (-kx ) dx = -k Xf ∫ xi xdx = ½ k x i 2 – ½ k x f 2 Work done by a spring force: W = ½ k (x i 2 – x f 2 ) W s > 0 -Is true if |x i | > |x f |-Block ends up closer to equilibrium W s < 0-Is true if |x i | < |x f |-Block ends up farther away from equilibrium-Think of a hand pulling a block away from the spring attached to it. (W a = -W s ) W = 0-Is true if |x i | = |x f |...
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## This note was uploaded on 04/04/2009 for the course PHYS 1020 taught by Professor Campbell-brown during the Spring '09 term at UWO.

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Physics October--20-08 - motion into small enough...

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