Work and Elastic Potential Energy

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# Work and Elastic Potential Energy - PowerPoint PPT Presentation

Work and Elastic Potential Energy. Work. Applying a force over a distance. W = F  ∆x The force can’t be zero. The distance can’t be zero. Three Cases. Force Parallel to Motion Speeds it up Increases Energy Positive work Force Anti-Parallel to Motion Slows it down

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Presentation Transcript

### Work and Elastic Potential Energy

Work
• Applying a force over a distance.
• W = F∆x

The force can’t be zero.

The distance can’t be zero.

Three Cases
• Force Parallel to Motion
• Speeds it up
• Increases Energy
• Positive work
• Force Anti-Parallel to Motion
• Slows it down
• Decreases Kinetic Energy

– Negative work

• Force Perpendicular to Motion
• Neither slows it down nor speeds it up.
• Doesn’t change Kinetic Energy
• Zero Work
Work of a Spring
• F = k∆x
• W = F∆x
• What is the force?
Work of a Spring

Work = Fave∆x = ½ k∆x*∆x = ½ kx2

Fundamental Theorem
• ΣW = ∆K
• The sum of all work equals the change in Kinetic Energy.
• Review HW Problems
• Check in:

A car of mass 1000 kg goes from a speed of 10 m/s to a speed of 20 m/s. How much work was done on the car?

• 150,000 J
Work and Potential Energy
• Work you do against gravity or against a spring is not lost but stored as potential energy.
• The amount of work you do is the amount of energy stored.
• For gravity your work is F*∆x = mg∆h
• What is the effect of the direction of the force compared to the direction of the motion?
• For a spring, your work is ½ kx2
• Us = ½ kx2
• Try problem 5 and 6 from the energy conservation worksheet.