What's the working principle of a tape measure that automatically shrinks back? It's best to give a schematic of the structure!
The first solution a little basic knowledge: the same shape of the object may be completely different stress state, such as the two springs on the instrument, may look as like as two peas, but actually different, one of them is completely relaxed, the other one is affected by a large force is compressed to such shape, there should be great force.The same concave section of the iron sheet, in the extension of the time is very different:Tape measure is very simple, basically in a relaxed state, originally this piece of iron, he is so shape. The concave surface is favorable for keeping shape and is difficult to deform.The thing you say can be wrapped around the arm is different. When stretched, it is not relaxed, and its original face should be curly. It is like straightening a coiled steel wire with a greater internal stress. It must use other forces to overcome its internal stress so as to prevent it from curling again and keeping it straight. The concave has just been said to have this ability. Therefore, the concave surface overcomes the tendency of the steel sheet to curl and maintains the straight extension state. Once the curl occurs, the concave tends to become flat, and the ability to maintain the extension decreases and the ability to curl exceeds the ability to maintain the extension, resulting in a steady state of the sheet as a whole.If you say a little more about it, the system is bistable. This is very common in life, such as beverage bottle, usually is a kind of stable state by hand pinch the concave is still stable, want to get out of the hollow place may also is not easy, want to take place also to convex pit big force.
It has a tape and the same no numerical counter force normae
It has a tape and the same no numerical counter force and Norma, bell like clockwork, you pull the foot, it is wound up, you loose, it will recover the anti tension tape.
