At first glance, the weakest part of any machine may seem to be its weakest link. But, as engineers and scientists learned long ago, there is plenty of potential for strength in a machine's weakest link. And for many purposes - from automobiles to spacecraft - that strength can be crucial.Take, for example, the automotive world. The engine is the weakest link in most cars, and the failure of that engine can often lead to a car's total failure. And yet, the engine is often the crucial component that allows a car to take off and travel down the road.