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Hunus

  • 4 years ago

Elastic potential energy

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  1. Hunus
    • 4 years ago
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    |dw:1335300188613:dw| When does the spring have negative potential energy?

  2. Hunus
    • 4 years ago
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    Does it?

  3. Vincent-Lyon.Fr
    • 4 years ago
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    Good question! Do you know the expression of this type of potential energy?

  4. Hunus
    • 4 years ago
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    \[\frac{kx^{2}}{2}\]

  5. Vincent-Lyon.Fr
    • 4 years ago
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    So...

  6. Hunus
    • 4 years ago
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    Well, when you have the equation \[F_x=-\frac{\partial U}{\partial x}\] what force does F_x represent?

  7. Hunus
    • 4 years ago
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    Because if F is the force of the spring, then wouldn't it be positive on the third picture? And if it was positive wouldn't dudx have to be negative?

  8. Vincent-Lyon.Fr
    • 4 years ago
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    Your problem is not asking about a negative force, but about a negative energy. For which x can ½kx² be negative?

  9. Hunus
    • 4 years ago
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    I'm reading through a book on classical mechanics and I'm having a difficult time understanding when the force is positive\[F_x=−\frac{∂U}{∂x}\]

  10. mos1635
    • 4 years ago
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    when F positive dx is negative??

  11. Vincent-Lyon.Fr
    • 4 years ago
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    Draw the function U(x)=½kx² For what values of x is the tangent to the curve positive/negative ? As Fx = -dU/dx, you will know the sign of Fx.

  12. Vincent-Lyon.Fr
    • 4 years ago
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    dU/dx is the derivative of U with respect to x. Its value is the gradient of the tangent to the curve at point (x,U(x)).

  13. Vincent-Lyon.Fr
    • 4 years ago
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    Quote : Well, when you have the equation Fx=−∂U/∂x what force does F_x represent? Answer : it reprensents the force exerted by the spring on the block.

  14. Hunus
    • 4 years ago
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    Thank you

  15. Vincent-Lyon.Fr
    • 4 years ago
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    Welcome :)

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