**Goal:** Hone the vector nature of force.

**Source:** UMPERG

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:

## 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.