Basic Structures for Engineers and Architects
As you may know, a tug of war is a physical competition involving two teams and a very long piece of rope. The two teams normally comprise equal numbers of contestants. Each team distributes itself along one end of the rope, as illustrated in Fig. 6.2. The team at the left end of the rope is using all its strength to pull the rope (and the opposing team) to the left. Similarly, the team at the right end of the rope is using all its strength to pull the rope to the right. If there is a river separating the two teams, the stronger team will eventually win by pulling the opposing team into the river.
Imagine that you are in London and are planning a journey on the Under- ground railway system there. You are at Green Park station and want to travel to Oxford Circus. You consult the diagram of lines and stations displayed at the station entrance, a representation of the relevant part of which is shown in Fig. 7.1. You work out that the quickest way to reach Ox- ford Circus from Green Park is to travel directly there on the Victoria Line. Oxford Circus is only one station from Green Park.
However, as you enter the station, you pass a blackboard on which has been written: ‘Victoria Line Closed due to Technical Diffi culties.’ Clearly, this news means you must change your travel plans. Assuming that you don’t now decide to walk or take a bus or taxi, there are two options avail- able to you if you wish to reach Oxford Circus as quickly as possible:
