Posted on: November 21st, 2018
A pulley is basically made up of, typically, 1, 2 or 4 wheels around which a rope or chain is looped. One of six simple machines developed by humans to make work easier; the other five are the wheel and axle, the lever, the screw, the wedge and the inclined plane.
Pulleys are used to either change the direction of the object (e.g. lifting it upwards) or to multiply the force applied to make lifting heavy objects easier or both.
When a rope or chain is pulled over the wheels it’s the science behind the way a pulley works that makes it easier to raise and or lower heavy objects. If you increase the number of wheels through which the rope passes, the more weight you will be able to lift.
The way the pulley operates means that your body strength can be multiplied by 2 or 4 times depending on how many wheels the pulley has.
So a pulley can make lifting heavy or irregular shaped objects easier and quicker.
With just one wheel you actually have no extra lifting advantage because if you want to lift a 20kg load up you will need to pull down on the rope/chain with an equal 20kg force using your own strength. The only real advantage of a single wheel pulley is that you will be pulling down on the rope and can, therefore, use your bodyweight to help and this is certainly easier than lifting the item up from the floor. This will also reduce the chances of back injuries and enable you to pick up awkwardly shaped items as long as they are connected to the pulley securely.
With a simple single wheel pulley, to lift something up 2 metres from the ground you will be required to pull down on the rope an equal 2 metres.
The pulley really starts to come into its own when you have a 2 or more wheel pulley, because with 2 wheels and the rope looped around them correctly you effectively halve the force (strength) you need to put into it to lift the same weight. So the 20kg weight mentioned above would now only require a downward force of 10kgs.
There is one slight drawback or trade-off in this halving of the effective weight and that is you would now need to pull the rope down 4 meters to lift the object 2 metres. So it’s a little bit like riding a push-bike up hill in a lower gear, it is easier to pedal but you have to do more revolutions.
The extra distance you need to pull the rope is because with two wheels even though you still have one rope, the way its wrapped around the pulleys makes it like having two ropes that need to move two meters each.
The technical term of how a pulley is advantageous is known as “Mechanical Advantage” and is an expression of the lifting “multiplier”. So as the mechanical advantage increases the effort needed reduces, though the distance you need to move the rope will increase by a proportionate amount.
So in an extreme example, an 8 wheel pulley would only require an effort of 1kg to lift an 8kg weight. It’s all about being efficient and using the pulley like a lever effect.
If you ever went on a see-saw as a young child with your Dad you obviously wouldn’t weigh nearly enough to be able to lift him up if you were both sitting equidistant from the centre of the see-saw. However, if your Dad was 4 times your weight and sat 4 times closer to the middle you would be able to see saw each other perfectly. You would be moving up and down 4 times as far as him and it’s the physics of force over distance that evens it out.
This is exactly the same as you pulling the rope four times as far with a four wheel pulley. (Anyway that’s enough science)
Pulleys are used in everyday life and you may not even realise it!
At Absolute Hardware we have an incredible range of pulley wheels and systems for you to choose from.
We offer pulleys with nylon wheels, cast wheels, single or double wheels, with hooks or screw eyes in black, galvanised, stainless steel or white finish and in a variety of sizes to suit your requirements.
Whether you are making repairs around the home or installing building work to your business premises don’t take a chance on inferior products get top quality pulleys made using proven techniques.
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