A2L Item 050
- Description: Consider statements about tension in a horizontal wire bearing a weight.
- Goal: Hone the vector nature of force.
- Source: UMPERG
- Keywords: Forces, Mechanics, Vectors
The question for students:
A thin wire is stretched horizontally between two walls. If a weight, W, is hung on the wire, what is true about the tension, T, in the wire?
- T < W
- T = W
- T > W
- The relationship between T and W cannot be determined.
Commentary for teachers:
Answers
(3); The vertical component of the tension force exerted on the weight must equal half the gravitational force. For a nearly horizontal wire this means the tension must exceed the weight.
Background
The intent is to get students to use their intuitive notions of balancing force to reason how directions of forces change the value of forces.
Questions to Reveal Student Reasoning
How do you determine the tension force? What direction does the tension force point? In (A) what does the tension force equal? Does it matter what angle the strings point? Explain.
Suggestions
Have some students try to lift an object with strings straight up and at an angle. Which is easier.
Set up a demonstration with spring scales.