10+ Year Member
Jul 16, 2008
Dental Student
I think there is an error in EK 30min In Class Exam Lect 3 #57. The question asks "how does friction between the 0.1 kg mass and the table in experiment 2 affect the results of the experiment?" I think the answer should be that the tension in the string is decreased by friction. But the solution says that the tension should increase because friction, being the force opposing the direction of tension, should increase the tension. Can someone confirm my speculation please? If the answer for this question should be increase, can someone explain the reason? I don't think the EK solution explains well. Many thanks. :)


Doctor Professor
10+ Year Member
Jul 6, 2008
Resident [Any Field]
Compare the "pulling action" with friction and without friction. The string tension is greater when there is friction present because you have to pull extra-hard to overcome the friction.

Alternatively, with no friction, let's say Tension = Force of no friction.

With friction, Tension = Force of no friction + force of friction.

(of course that is not the real equation, but that is why it is greater - you must overcome a greater force, which is transmitted through your string (at an equivalently higher tension))
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