Lighting Bar Hangers - seeking

[sunray]

i.e. the total load on the top anchor pulley hasn't changed, but the effort needed for lifting has reduced. I believe they call it Conservation of Energy.

 

That isn't so though. The total load on the fixing of the top pulley goes down the more purchase you put on it. A 2 pulley system lifting 100Kg only puts 150kg load on the top fixing; a 1 pulley system puts 200kg load on the top fixing.

I am not sure you are right about your lever/fulcrum point either, I think if you put 10kg at 10x the distance the down force on the fulcrum is now only 110Kg.

 

 

(sorry for measuring force in kg but you know what I mean)

I'm happy with weight, I know I can hang a 10Kg weight but I don't have a box of Newtons?.

If there is 100Kg at one end and 10Kg at the other, the total on the fulcrum is 110Kg ignoring the weight of the bar etc.

[sandall]

Wrong.

If you have 100kg on each side then yes, you fulcrum is supporting 200kg.

But when you have 100kg and 10kg its only supporting 110kg

The Weight, if you picked it up & carried it away, would be 110Kg, but, assuming the load is 1m from the fulcrum, to balance its 100Kg/metre downward Force (which is what matters) you need to apply an equal downward force of 100Kg/metre on the other side, regardless of whether it's 100Kg at 1m or 10Kg at 10m. It's not the weight that brings the bar down on your head - it's the downward forces on its fixings.

 

Oh, I wish Frank Wood was still alive - he would eloquently prove us all wrong.

 

I try to steer clear of Newtons - there's enough confusion around between force & mass (or weight if you prefer) without adding acceleration to the mix :(

Edited November 5, 2019 by sandall

[Junior8]

I'd use a chain block anyway!

[timsabre]

Err now you're talking about moments (turning force). The downward force on the fulcrum would just be the sum of the weights wherever they are placed. (neglecting the weight of the bar)

[sandall]

Retires hurt :(

[timsabre]

The whole thing really hurts my brain but I think what I put above is right

[Jivemaster]

Add into that the snatch force every time someone pulls hard and the inevitable friction in every bearing surface, more pulleys means better advantage but greater friction.

[sunray]

Wrong.

If you have 100kg on each side then yes, you fulcrum is supporting 200kg.

But when you have 100kg and 10kg its only supporting 110kg

The Weight, if you picked it up & carried it away, would be 110Kg, but, assuming the load is 1m from the fulcrum, to balance its 100Kg/metre downward Force (which is what matters) you need to apply an equal downward force of 100Kg/metre on the other side, regardless of whether it's 100Kg at 1m or 10Kg at 10m. It's not the weight that brings the bar down on your head - it's the downward forces on its fixings.

 

Oh, I wish Frank Wood was still alive - he would eloquently prove us all wrong.

 

I try to steer clear of Newtons - there's enough confusion around between force & mass (or weight if you prefer) without adding acceleration to the mix :(

 

Yes you are right it is the force but force can ultimately be quoted as weight from first principles.

 

I so hope you are not referring to Frank Woods from the Medway Towns - biggest BS'er ever

 

Err now you're talking about moments (turning force). The downward force on the fulcrum would just be the sum of the weights wherever they are placed. (neglecting the weight of the bar)

Correct.

 

I'd use a chain block anyway!

Indeed but the principles still apply but don't forget - a lot of weight is added by the block.

 

[indyld]

Retires hurt :(

 

F=MA = FML.

[Junior8]

I'd use a chain block anyway!

Indeed but the principles still apply but don't forget - a lot of weight is added by the block.

 

 

Agreed but in the case of a basic one a total device weight of 9kg for a WLL of 500 kg 9 m lift is a reasonable trade off.

[kerry davies]

Three whole pages of waffle and the answer, as always, is; fetch the telehandler.

[david.elsbury]

Three whole pages of waffle and the answer, as always, is; fetch the telehandler.

My, you’re grumpy today!

Why is the telehandler the best option here?!? We’re not talking about moving stillages around. We want to know about strut type brackets.

Edited November 7, 2019 by david.elsbury

[kerry davies]

That's where we started but we ended up hauling 100kg luminaires into the sky on ropes, hence the lighthearted mention of telehandlers. The OP got his answer by the second response and after 36 more it was definitely time to jump this shark.

 

I mean, Roger (Junior8) even started replying to himself.

[kerry davies]

double post, sorry. Edited November 8, 2019 by kerry davies

[david.elsbury]

Right.... I think I see...