MHB What Is the Equivalent Linear Spring Constant at Steady Deflection?

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The discussion revolves around determining the equivalent linear spring constant for a steel helical spring with a given force-deflection relation \(F(x) = 200x + 50x^2 + 10x^3\). The steady deflection of \(0.5\) inches is specified, but the force \(F\) is not directly provided, complicating the calculation. Participants clarify that "steady deflection" refers to the spring being at a fixed position during operation. The correct equivalent linear spring constant at this deflection is calculated to be \(253.75\) lb per inch. The terminology used in the problem is noted as coming from the textbook, with some confusion addressed regarding the distinction between Hooke's Law and Newton's laws.
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The force-deflection relation of a steel helical spring used in an engine is found experimentally as \(F(x) = 200x + 50x^2 + 10x^3\), where the force \((F)\) and deflection \((x)\) are measured in pounds and inches, respectively. If the spring undergoes a steady deflection of \(0.5\) in during the operation of the engine, determine the equivalent linear spring constant of the spring at its steady deflection.

If I knew \(F\), I could simply solve the cubic for the real \(x\) and then use the Newtons 2nd law \(F = k_{eq}x\).

In this problem, I don't have \(F\) instead I have the steady deflection. How do I solve this type of problem?

The answer is \(253.75\) lb per in
 
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dwsmith said:
The force-deflection relation of a steel helical spring used in an engine is found experimentally as \(F(x) = 200x + 50x^2 + 10x^3\), where the force \((F)\) and deflection \((x)\) are measured in pounds and inches, respectively. If the spring undergoes a steady deflection of \(0.5\) in during the operation of the engine, determine the equivalent linear spring constant of the spring at its steady deflection.

If I knew \(F\), I could simply solve the cubic for the real \(x\) and then use the Newtons 2nd law \(F = k_{eq}x\).

In this problem, I don't have \(F\) instead I have the steady deflection. How do I solve this type of problem?

The answer is \(253.75\) lb per in
What do you mean by "steady deflection?" It sounds like the spring is at a particular point and doesn't move?

Also, F = kx is Hooke's Law, not Newton's.

-Dan
 
topsquark said:
What do you mean by "steady deflection?" It sounds like the spring is at a particular point and doesn't move?

Also, F = kx is Hooke's Law, not Newton's.

-Dan

That is just the terminology the book uses.
 
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