Download - Chapter 5.2 Hooke’s Law
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Chapter 5.2 Hooke’s Law
WOD are underlined
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Question What is the net force on this mass?
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Question What about now? What direction will the force be?
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Hooke’s Law Springs are objects that store energy
and create forces in order to restore
themselves to equilibrium.
Springs create NON-CONSTANT forces that are always towards the direction of equilibrium.
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Hooke’s Law (WOD) F = - k Δx
New Symbol: “k”
k is Spring constant. “Stiffness” of the spring. Depends on each spring’s dimensions and material.
In N/m
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Hooke’s Law F = - k Δx
Force = stiffness of spring (or k) times
How far you stretch it
The negative sign reverses the direction of Δx.
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More about the negative sign The force exerted *BY* a spring is opposed to the displacement.
The force applied *ON* a spring will be equal and opposite to that. You have to push on a spring to compress it.
You have to pull on a spring to stretch it.
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Problem A: A spring with spring constant 10 N/m has a force of 40 N applied to it (stretching it). How much does the spring stretch?
F = - k Δx
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Problem A: A spring with spring constant 10 N/m has a force of 40 N applied to it (stretching it). How much does the spring stretch?
X = 40N / (-10N/m)
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Another problem B: A force of 600 Newtons will compress a spring 0.5 meters. What is the spring constant of the spring?
F = - k Δx
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Another problem B: A force of 600 Newtons will compress a spring 0.5 meters. What is the spring constant of the spring?
k = -F / Δx = -600N / (.5m)
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Question If I let go, what will happen to the mass? Then what? Then what?
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Question If I let go, what will happen to the mass?
For how long? Why would it stop?
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Question For how long? Why would it stop?
Go on forever, unless friction or until friction sucks away all the energy. Then it stops.
What friction is there?
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Simple Harmonic Motion Motion that occurs when the net force obeys Hooke’s Law The force is proportional to the displacement and always directed toward the equilibrium position.
The motion of a spring mass system is an example of Simple Harmonic Motion
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Classwork: Section 5-2 Pg 172 Prob 21-29 Staple to 5-2 Read and Write and turn in. HW due Tuesday. Read and Write for 13.1 and 13.2 HW due Weds. Read and Write 13.3-.5
You can play around with Bike wheels if you wish to do probs at home.