mechanical · 28 minutes · Official OETT Aligned
Ropes & Pulling Force
How rope angle changes the pull in each rope
What to know
- tension: pulling force in a rope
- sharing a load
- angle above a horizontal line
- upward and sideways pull
Two ropes do not always carry a pulling force equal to half the load. Their angles matter.
The core rule
As two supporting ropes spread farther apart, each rope needs more tension to hold the same load.
Tension is the pull along a rope. Two vertical ropes can each carry half of a centered load. With angled ropes, part of each pull acts sideways, so a larger total pull is needed to provide enough upward force. Flatter ropes need more tension than steeper ropes.
Worked examples
Example 1: easy
Two vertical equal legs share a centered 200-lb load at about 100 lb each.
- Both ropes are vertical and share a centered load equally.
- Divide: 200 ÷ 2 = 100 lb of tension in each rope.
All of each rope pull acts upward in this setup.
Example 2: medium
A symmetric 60° sling has lower leg tension than a 30° sling for the same load.
- Measure both rope angles above a horizontal line. The 60° ropes are steeper than the 30° ropes.
- More of the pull from steeper ropes acts upward, so they need less total tension.
Flatter ropes pull more sideways and need more total force for the same lift.
Example 3: hard
If two supporting ropes have different angles, how do you check the pull in each?
- Draw each rope pull along its own angle. Split each into an upward part and a sideways part.
- The sideways parts must cancel. The upward parts must add up to the load.
Different rope angles mean you cannot simply assume equal tension.
Common mistakes
Each of two ropes always has tension equal to half the load.
That only works for two vertical ropes sharing the load equally. Angled ropes need more tension.
Put it into practice
Use guided explanations, check your answers, and try a new variation.