How does block tackle work

In antiquity, block and tackles were used in construction projects to move heavy loads. In the modern era, they are used frequently on boats where it would be impractical to have a crane or other heavy lifting machinery. If we were attempting to lift a lb. We would put one pulley in the rafters and pass a rope through it, attaching one end of the rope to the crate.

By pulling the other end of the rope the hauling part , we could lift the crate into the rafters. In this system, each time we pull the rope one foot with lbs. Lifting with anything less than lbs. If, instead of attaching the rope directly to the crate, we passed it through a new pulley attached to the crate and then attached the end of the rope to the rafters, we would have a block and tackle.

Now, each time we pulled the free end of the rope, the rope would have to travel between the rafters and the crate twice. We would have to pull two feet on the rope to lift the crate a single foot. However, we would only have to pull with lbs.

This disparity between the amount of force required to move an object and the weight of the object is the mechanical advantage of the block and tackle. This is the same as the disparity between how much rope we pull compared to the distance the object moves.

To calculate the mechanical advantage, we can either divide the weight of the object being lifted by the force required to lift it or we can divide the amount of rope we have to pull by the distance the object moves.

A block and tackle rigging holds an advantage when the rope is pulled in the same direction that the load will be moved. It is rigged to disadvantage when it is being pulled in the direction opposite of where the load is to be moved pulling down on a load to be lifted, for example.

If you have a single wheel and a rope, a pulley helps you reverse the direction of your lifting force. So, as in the picture below, you pull the rope down to lift the weight up. If you want to lift something that weighs kg, you have to pull down with a force equivalent to kg, which is N newtons. Pulleys consist of a wheel that rotates on an axle—which is a rod through the center of the wheel—and a rope, cable, or chain.

There are three main types of pulleys : fixed, movable, and compound. A fixed pulley's wheel and axle stay in one place. You can add or subtract pulleys from the system. More pulleys makes it easier to pull or they allow you to pull a heavier load , but you have to pull more rope to move the load by the same amount. Many different types of pulley systems exist. Attach the rope first to the bottom of the upper fixed pulley , then loop the rope down through the wheel on the moveable lower pulley.

Now, loop the rope back up through the top fixed pulley. Make sure the rope is fully seated into the grooves on the pulley wheels. Suppose you could rig up a pair of pulley systems and get a friend, who is as strong as you, to pull one of them. You'd still have trouble, but you might be able to do it because each pulley would lift half the weight , or 1, pounds, and a quarter of that weight is pounds.

To do this, you divide the distance from the fulcrum, the point at which the lever pivots, to the applied force by the distance from the fulcrum to the resistance force. Using this picture, this means dividing distance b by distance a. Again, higher mechanical advantages equate to doing less work. A pulley system makes it easier to lift an object than lifting the dead weight by hand.

A single pulley essentially changes the direction of the pull or force applied. When a person uses two or more pulleys in a system, then the system also multiplies the force applied besides changing its direction. How to Make a Pulley Hoist Locate two cross-beams in the ceiling where you can securely install the screw-in hooks.

Screw the hooks into the ceiling until they are flush, or securely mounted. Hang a double pulley on one hook and a single pulley on the other. Let's also say that the radius of the left-hand cylinder is 0. If the radius of the right-hand cylinder is 4 times greater, or 2. If you push the left-hand piston down through 16 inches with a force of 10 pounds, then the right-hand piston will rise 1 inch with a force of pounds. Hydraulic cylinders of all sorts take advantage of this simple force-multiplying effect every day.

You can see that a block and tackle, a lever, a gear train and a hydraulic system all do the same thing: they let you magnify a force by proportionally diminishing the distance through which the magnified force can act. It turns out that this sort of force multiplication is an extremely useful capability!

Here are some of the devices that use these simple principles:. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. How a Block and Tackle Works. Car jack lever or threaded gear Fingernail clippers lever Automobile transmission gears Come-along block and tackle, gear Can opener gear, lever Crowbar lever Hammer claw lever Bottle opener lever Car brakes hydraulics Hydraulic shop lift Elevator block and tackle Etc Pulley FAQ How do pulleys work?

A pulley is a wheel on an axle designed to assist in the movement of heavy loads. A one-wheel pulley allows you to change the direction of the force you have to apply to lift the load by pulling down to lift a load upwards. Similarly, a two-wheel pulley splits the weight equally so that each holds only half the weight, allowing you to lift the same weight with half of the force. Where are pulleys used?