Friction question

[Warwick]

I was looking at how a problem was solved and what I did not get was why T was put in this equation or n. I'm a little confused on the tension stuff. I do get how friction works and it's coefficiant. n and T is confusing me. The n is the weight of the object on the surface, I know, but why is it in these equations.

Sum of Fx=T-fk=ma
Sum of Fy=n-m1g=0

Thanks

[NiteCrawler]

you need to ask a more specific question ... Problems solving for this kind of problems mostly depend on a free body diagram. T usually stands for tension eg. tension of a string, and n is the normal force acting on an object. The weight of an object W is the mass times gravitational accleration (-g = -9.8m/s^2, Earth system). Hope this answer your question