1. The thickness of the metallic ropes used in cranes is decided on the basis of the elastic limit of the material of the rope and the factor of safety.
2. To lift a load upto 104 kg, the rope is made for a factor of safety of 10.
3. It should not break even when a load of (original load × factor of safety = 104 × 10) 105 kgf i.e., 105 × 9.8 N is applied on it.
4. If ‘r’ is the radius of the rope, then maximum stress = \(\frac{10^5}{\pi r^2}\).
5. The maximum stress (ultimate stress) should not exceed the breaking stress (5 to 20 × 108 N/m2) as well as elastic limit of steel Ys (30 × 107 N/m2).
6. In order to have flexibility, the rope is made up of large number of thin wires twisted together.
