Science Buddies: "Ask an Expert"

Hello,-I am completing the Deep Knee bends Project. I have constructed the knee and measured the length of the spring when the knee is bent at a 30,60 and 90 degree angle. I measured the length of the spring in centimeters. I use the F=-kx from the deep knee bends project found on this website. I want to confirm that once I work out the problem the answer would be the amount of Newtons? Also with this formula since there is a negative it is appearing that less force is needed for a larger angle this doesn't seem correct. Will you clear this up for me please.

Hello,
The answer you get should be in Newtons if you use SI units in your measurements (meters, kilograms, and such). And for your other question, F =-kx is the force that the spring acts on the joint with. Since force is a vector, it has a numerical part and a directional part. Take, for example, 50N of force exerted on a body by gravity. The number is 50, and the direction of the force is down (because gravity works downwards). Now since the conventional method says that + numbers represent forces going up, so this downwards force can be conveyed as -50N on that body. So the negative you're getting just tells you the direction in which the force you are measuring is acting on, not conveying how small the force is.

I hope this helps!
Meg