How Does Spring Force Affect Net Force in Physics?

[Jaccobtw]

Homework Statement

Why is there a negative on the spring constant in this equation?: F = -kd

Relevant Equations

F = -kd

Let's say you have a box and there is a spring attached to it and the other end of the spring is attached to the wall. If you press the box towards the wall the spring presses back against the box with an equal force. F(push) = 20N, F(spring) = -kd. F(push) - F(spring) = F(net). Which is zero. However, because there is a negative, and because I am subtracting a negative, you get a much larger positive number of net force. Isn't this incorrect?

 

[berkeman]

The negative sign shows that the restoring force is in the opposite direction from the displacement (hence "restoring" force). The negative sign is associated with the displacement, not with the spring constant.

Does that help?

 

[berkeman]

BTW, keep asking good questions!

 

[BvU]

What also helps is a sketch of the situation, showing which way you consider positive...