Strechable cord - what sensor for measure pulling force?

Hello.
I am quite new to arduino and hardware components.
I would like to build a case with a cord looking out of it and the harder I pull that cord, the higher the data value, which I would like to send to my PC, should be.
Alternatively, I could also roll up a polyester cord inside the case and would like to get a value of how far I pulled out that cord. Both ways would fit into my project, yet I do not know with what kind of sensors and components I could achieve it. I hope I am in the right place to ask.

Thank you.

crazynexx:
I would like to build a case with a cord looking out of it and the harder I pull that cord, the higher the data value, which I would like to send to my PC, should be.

Look at load cells.

crazynexx:
Alternatively, I could also roll up a polyester cord inside the case and would like to get a value of how far I pulled out that cord.

Look at "string encoder" or "stringpot". I've heard you can do a DIY one of these using one of those retractable keychains.

Search for "luggage weight" on ebay.
There's probably some pull load cell inside.
Leo..

Thank you very much. Your answeres gave me quite the input i was looking for. I guess the string encoder might be the cheapest and easiest way to go.