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Mechanical Advantage explained:
The following is a hypothetical series of events that has may have a surprise conclusion for you.
Lets say you are a very fit 180 lbs. You can do a dozen pull ups and bench at least 200 lbs.
Your son is sailing with you and he is an athlete that weighs 140 lbs can do 20 pull ups and bench well over 200 lbs. In other words you are both very fit, but the kid can do anything you can do physically and then some.
On a sail you find the the anchor light bulb has burnt out and you decide to climb up the mast to replace it. You don't have all the right gear but you do have a couple hundred feet of line and a block handy so you figure you will just hoist up the block with the main halyard and a blight of the line. You figure that you are in good enough shape to do 20 pull ups with your full weight and if you rest a bit at the spreaders you can do a second set and make the top.
You start out doing really well, in fact it seems easier than you figured. But about half way you start to get a cramp, probably all the beer the night before.
Your kid is on deck shouting encouragement so you figure you will let him pull you the rest of the way up.
As soon as your son gets his hand on the down line you let go and expect him to hoist you up.
What happens is a surprise to both of you.
You start to fall and your son is lifted right off the deck headed your way.
What happened.
As long as you were tailing your own line you only had to pull 90 lbs, just half of your weight plus a little for friction. As soon as your son on deck had the line and you let go the weight he has to pull jumps to 180 lbs. Regardless of his grip since he only weights 140 lbs he is going to go up and you are going to go down.
The fact that the guy in the chair only has to handle half the weight of the guy on the ground seems at first look more than a little strange, but the math works.
The following videos explain is well:
https://www.youtube.com/watch?v=76l9KZ6XcME
https://www.youtube.com/watch?v=v1p-xuZNq5g
The following is a hypothetical series of events that has may have a surprise conclusion for you.
Lets say you are a very fit 180 lbs. You can do a dozen pull ups and bench at least 200 lbs.
Your son is sailing with you and he is an athlete that weighs 140 lbs can do 20 pull ups and bench well over 200 lbs. In other words you are both very fit, but the kid can do anything you can do physically and then some.
On a sail you find the the anchor light bulb has burnt out and you decide to climb up the mast to replace it. You don't have all the right gear but you do have a couple hundred feet of line and a block handy so you figure you will just hoist up the block with the main halyard and a blight of the line. You figure that you are in good enough shape to do 20 pull ups with your full weight and if you rest a bit at the spreaders you can do a second set and make the top.
You start out doing really well, in fact it seems easier than you figured. But about half way you start to get a cramp, probably all the beer the night before.
Your kid is on deck shouting encouragement so you figure you will let him pull you the rest of the way up.
As soon as your son gets his hand on the down line you let go and expect him to hoist you up.
What happens is a surprise to both of you.
You start to fall and your son is lifted right off the deck headed your way.
What happened.
As long as you were tailing your own line you only had to pull 90 lbs, just half of your weight plus a little for friction. As soon as your son on deck had the line and you let go the weight he has to pull jumps to 180 lbs. Regardless of his grip since he only weights 140 lbs he is going to go up and you are going to go down.
The fact that the guy in the chair only has to handle half the weight of the guy on the ground seems at first look more than a little strange, but the math works.
The following videos explain is well:
https://www.youtube.com/watch?v=76l9KZ6XcME
https://www.youtube.com/watch?v=v1p-xuZNq5g