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Hello,

I hope this is a suitable forum, it's a million miles from homework but it may be on the same sort of level.

A picture is worth a thousand words so please have a look at the attached picture. When the rope is pulled there isn't just the issue of gravity, but also of the friction of the rope over the metal bar. What I am wanting to calculate is the actual force that must be applied to stop the weight from falling, taking into account the friction.

I really don't know where to start with this, but from the searching that I've done, this page seems to be using diagrams and words that seems applicable. http://www.engineeringtoolbox.com/bollard-force-d_1296.html

The equation given is:

S = F e

Where:

S = effort force in the rope (N)

F = load (N)

e = 2.718

μ = friction coefficient (approximately 0.3 - 0.5 is common for a rope around a steel or cast iron bollard)

α = angle where the rope is in contact with the bollard (radians)

So, plugging in the following data (assuming the rope is only in contact with half the bollard):

F = 300N

e = 2.718

μ = 0.4

α = ∏

I get:

300 * ( 2.718

Which seems to imply that the force that is needed to stop the weight from falling is 214.6 1N (300-85.39). However, I've got a feeling that I might be messing up the calculation, would somebody be kind enough to take a look for me?

Thank you.

I hope this is a suitable forum, it's a million miles from homework but it may be on the same sort of level.

A picture is worth a thousand words so please have a look at the attached picture. When the rope is pulled there isn't just the issue of gravity, but also of the friction of the rope over the metal bar. What I am wanting to calculate is the actual force that must be applied to stop the weight from falling, taking into account the friction.

I really don't know where to start with this, but from the searching that I've done, this page seems to be using diagrams and words that seems applicable. http://www.engineeringtoolbox.com/bollard-force-d_1296.html

The equation given is:

S = F e

^{-μα}Where:

S = effort force in the rope (N)

F = load (N)

e = 2.718

μ = friction coefficient (approximately 0.3 - 0.5 is common for a rope around a steel or cast iron bollard)

α = angle where the rope is in contact with the bollard (radians)

So, plugging in the following data (assuming the rope is only in contact with half the bollard):

F = 300N

e = 2.718

μ = 0.4

α = ∏

I get:

300 * ( 2.718

^{-0.4 * ∏}) = 85.39 NWhich seems to imply that the force that is needed to stop the weight from falling is 214.6 1N (300-85.39). However, I've got a feeling that I might be messing up the calculation, would somebody be kind enough to take a look for me?

Thank you.