# Calculate forces and speed on a zipline

1. Jul 17, 2013

### sytseelzinga

Hi,

First of all, this is not my expertise so I'm sorry for things that are noted wrong. I would like to know some things about a zipline I'm going to build.

• Velocity of a person after 60 and 74 meters
• Forces on the anchor points
• (wind) Forces on the building
• Forces on the ankerpoints when someone needs to be rescued.

Here is a picture for clarification:

I could find things about ziplines, speeds and forces, but not including friction, not-moving or moving objects.
• No persons heavier than 100 kg are allowed
• Rescue situation: 100 kg victim + 80 kg rescuer, hanging still in the middle
• rope used: Polyester (for friction coefficient, model: Black Marlow rappeling rope)
• pulley: steel (mode: petzl speed)
• friction must be included
• The zipline is tensioned by 'haulers' max force: 300 kg
• I'd appreciate some formulas + explanation, so I can help others as well.

I really appreciate the help. And I want to let you know, I'm going to build a webbased calculator after this to help others as well.

Gr. Sytse

2. Jul 17, 2013

### polomeister

Hi, whilst it's an interesting physics problem, I really think you should get professional advice on setting this thing up (and make sure they have insurance cover) and do not implement any solution posted on here before it is signed-off by a professional. I'd strongly recommend not setting up a web-based calculator as you could get sued if somebody's zipline fails.

3. Jul 17, 2013

### sytseelzinga

Hi Polomeister,

Thank you for your reaction. The insurance issue is not a problem in this case. That's already covered. It's just for the background info. Ziplines are always tested (in levels) by the way, so even if there's a calculation error, it will always come out.

About the web-based calculator: it's just to show people what forces/velocities are involved. If they use the calculator they agree with a certain kind of terms (checkbox or something like that).
But thanks for the notification/tip!

4. Jul 17, 2013

### polomeister

OK! As long as it's purely for interest, I posted a workbook earlier today that might get you started.

1. You'll effectively need to rotate the line (this could be done by simply rotating the direction of the "const force")
2. Start with the mass at one end, with zero velocity
3. You'll need to add a couple of columns into the Force calculation for resistance. My understanding this is linear in velocity for slow speeds but increases to quadratic for higher speeds (but I don't know the boundary)
4. You'll need to input the elasticity constant. I have no idea what this is for your line
5. Note the assumptions/limitations. If someone else works it out for you exactly, I'd be interested to see how their answers compare to the workbook

Best wishes

P

5. Jul 18, 2013

### sytseelzinga

Thanks again, it looks very nice and interesting but it's out of my expertise, sorry.

btw: If I get other professional help / input for the issue I'll post it here.

6. Aug 15, 2014

### Staff: Mentor

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