[Work and Energy] Work positive or negative?

[hiuting]

Homework Statement

I don't know when the work of a spring is negative, and when it's positive... When is the work of a spring negative and when is it positive?

Homework Equations

W_sp= -(1/2)(k)(xf²-xi²)

The Attempt at a Solution

I can get Wsp to be positive when the spring is stretch, but I want to know the theory behind it.

 

[bleedblue1234]

When does a spring oppose motion?

think about it in your everyday life pushing and pulling a spring

 

[rock.freak667]

It's a sign convention. When a spring is compressed, something does work on the spring. So the work done by the spring is negative.

When the spring stretches, the spring does work on the 'something', so the work done is positive.

 

[bleedblue1234]

but negative work means opposing motion, therefore the spring always does negative work