How do levers help make work easier

A third class lever has less of a mechanical advantage than the other two types because the distance from the load to the fulcrum is greater than the distance from the effort to the fulcrum. Annawaldl, public domain image via Pixabay. Using a crowbar as a lever to lift a heavy piece of stone.

Public domain image via Pixabay. An excavator digger has several connected levers on its boom. Hydraulic cylinders produce the force required to move the levers. Didgeman, public domain image via Pixabay. To understand how levers work, we first need to understand the concept of moment of a force. The moment of a force about a point is the magnitude of the force multiplied by the perpendicular distance from the point, to the line of direction of the force.

In the diagram below, two forces act on the lever. This is a schematic or diagram, but it symbolically represents any of the real life levers mentioned above. The lever pivots at a point called a fulcrum represented by the black triangle in real life, this could be the screw holding the two blades of a scissors together.

A lever is said to be balanced when the lever doesn't rotate and everything is in equilibrium e. In the diagram above, a force F1 acts downward on the lever at a distance d1 from the fulcrum.

When balanced:. Another force F2 at distance d2 from the fulcrum acts downwards on the lever. This balances the effects of F1 and the lever is stationary, i. And when the lever is balanced, i. Imagine if F1 is the active force and is known. F2 is unknown but must push down on the lever to balance it. So F2 must have this value to balance the force F1 acting down on the right hand side. Since the lever is balanced, we can think of there being an equivalent force equal to F2 and due to F1 , shown in orange in the diagram below, pushing upwards on the left side of the lever.

This is intuitively correct since we know how a long crowbar can create a lot of force for lifting or prying things, or if you put your fingers between the jaws of a pliers and squeeze, you know all about it! This force magnifying effect or mechanical advantage of a lever is one of the features that makes it so useful. When the lever is balanced, the force F1 produces an equivalent force of magnitude F2 shown in orange.

This balances F2 shown in blue acting downwards. Many of the bones in your body act as third class levers. For instance in your arm, the elbow is the pivot, the biceps muscle creates the effort acting on the forearm and the load is held by a hand.

The small bones in the ear also form a lever system. These bones are the hammer, anvil and stirrup and act as levers to magnify sound coming from the eardrum. To conclude, we find that the physical geometry of a pulley system requires its mechanical advantage to always be greater than 1 and only in positive integer values; i. Figure The mechanical advantage of a pulley. Before stating the mechanical advantage of a wheel-and-axle, it is extremely important to remember that the effort is always applied to the wheel, while the load always acts to resists the turning motion of the axle.

Then from the general definition, we see the mechanical advantage of the wheel-and-axle depends only on the radius of each, where it can be written as:. This result informs engineers how the mechanical advantage of a wheel-and-axle may be altered to provide the most efficient results in an engineering system. Typically, engineers configure the wheel-and-axle so its mechanical advantage is greater than 1 to benefit from a magnified torque, such as the case with a steering wheel.

The mechanical advantage of the wheel-and-axle. All simple machines are characterized by their ability to provide mechanical advantage, which allows engineers to design devices to make work easier and more efficient. Although one machine is not superior to another, each machine provides its own unique and attractive capabilities which are used by engineers for numerous applications. The lever is capable of quickly increasing either force or distance; the pulley can lift enormous loads over a vertical path; and the wheel-and-axle is used to easily increase an input torque.

These three simple machines, combined with the other three inclined plane, wedge and screw , give engineers a set of extremely valuable tools to effectively carry out work. This machine is primarily used to lift heavy loads along a direct vertical path.

Simple machines can exist on their own and are also sometimes hidden in the mechanical devices around you; a device which performs work by increasing or changing the direction of force, making work easier for people to do. This machine is primarily used to magnify a torque supplied by the user. Tally the votes and write the numbers on the board. Give the right answer. Team Competition : Organize the class into small groups of two or three students each and challenge each group to think of where in engineering systems today the lever, pulley and wheel-and-axle can be found.

The group that thinks of the most machines is the winning team. To get full credit, each team must state the engineering device along with the associated simple machine.

Examples: Lever: seesaw, balance scales, crowbar, wheelbarrow, nutcracker, bottle opener, tweezers, fishing rod, hammer, boat oar, rake, etc. Pulley: crane, elevator, flagpole, etc. Wheel and Axle: screwdriver, steering wheel, bicycle gears, doorknob, etc.

A complex machine is one that operates by combining two or more simple machines together. Consider a pair of scissors. The two arms that you squeeze together are levers , while the cutting edges of the blades are sharp wedges. The scissors were a solution to a real-world problem that was made simple by breaking it down into smaller pieces. The simple machines of a lever and wedge were combined to create an engineering solution. In groups of two, think about the following complex machines.

For each complex machine, list the simple machines that have been combined and where they are found just like the description of the scissors :.

Kahan, Peter. Environment: Hand Tools for Trail Work. Las updated June 16, Federal Highway Administration, U. Department of Transportation. Accessed August 31, Woods, Michael, and Mary Woods. Ancient Machines: From Wedges to Waterwheels. Minneapolis, MN: Runestone Press, However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Why Teach Engineering in K? Find more at TeachEngineering. Quick Look. Simple Machines Pulleys. Print this lesson Toggle Dropdown Print lesson and its associated curriculum.

Suggest an edit. Discuss this lesson. Curriculum in this Unit Units serve as guides to a particular content or subject area. Levers raise and lower an object as force is exerted upon the lever. An example of a lever is a bottle-opener: the handle acts as a lever arm, and the pivot that fits under the rim of the cap acts as a fulcrum.

A pulley is a wheel with a grooved rim that is used to reduce the amount of force and change the direction of force needed to do work. A fixed pulley is used to change the direction of force needed to do work; in order to hoist up a load with a pulley and rope, force is exerted downward on the rope. Since it is easier to pull down using your own weight than to pull upwards, fixed pulleys are commonly used.

A moveable pulley is attached to a load and is used to reduce the amount of force needed to do work. It slides along a rope, rather then a rope sliding along it.

A block and tackle is a combination of fixed and moveable pulleys, and is used to both change the direction and the amount of the force needed to do work. An example of a wheel and axle is an old-fashioned well, where a wheel is turned in order to crank the connected axle around, and the rope that the water pail is attached to then wraps around the axle. A wheel turns because of effort force and resistance pushing against it; the force can be exerted on either the axle, or the wheel.

The example of an old well is a case of the force turning the wheel. An example of the force being applied to the axle is on a Ferris Wheel: the wheel spins because of the force on the axle.

The term mechanical advantage is used to describe the number of times a simple machine multiplies the effort force applied. This ratio gives an idea of the effectiveness of a simple machine in reducing work. All more complex machines use at least one form of simple machine. A good activity for demonstrating this is to look at some common household machines with your children, and see if they can identify any of the simple machine parts.

The screw and the wheel and axle on a hand powered drill, and the screw and lever on a car jack, are examples of simple machines that are used in more complex ones. A lever is a board or a bar that turns on a fixed support called a fulcrum. Fingernail clippers are an example of levers. The force exerted on the handle of the clippers compresses the blades of the clippers so that they trim the fingernail. You might want to look at a pair of clippers with your children, and see if they can identify the fulcrum the pivot joint between the two parts, in this case.

Nail clippers are first class levers. You can make your own first class lever, using a ruler with a pencil to work as the fulcrum. You might want to mention other types of first class levers to your children; a seesaw is one example. A second class lever has the load located in the middle of the ruler, with the fulcrum on one side and the effort on the other.

Using a spring scale that measures in newtons, you can identify the mechanical advantage. If you have not already done so, you will need to find the weight of your load. Hook the load onto the spring scale, and record the weight in newtons.

The lever arm should have one end resting on the fulcrum, with the load placed at the center of the lever arm. Hook the spring scale to the lever arm at the end that is opposite the fulcrum, then pull up on the spring scale to lift the load. To lift an object that is twice as heavy, it takes twice as much work to lift it the same distance.

It also takes twice as much work to lift the same object twice as far. As indicated by the math, the main benefit of machines is that they allow us to do the same amount of work by applying a smaller amount of force over a greater distance. While it may be a bit of an exaggeration, it does express the power of leverage, which, at least figuratively, moves the world. The genius of Archimedes was to realize that in order to accomplish the same amount or work, one could make a trade-off between force and distance using a lever.

His Law of the Lever states, "Magnitudes are in equilibrium at distances reciprocally proportional to their weights," according to "Archimedes in the 21st Century," a virtual book by Chris Rorres at New York University.

The lever consists of a long beam and a fulcrum, or pivot. The mechanical advantage of the lever depends on the ratio of the lengths of the beam on either side of the fulcrum. For example, say we want to lift a lb. We can exert lbs. However, if we were to use a foot 9 m lever with one end under the weight and a 1-foot However, we would have to push the end of the lever down 4 feet 1.

We have made a trade-off in which we doubled the distance we had to move the lever, but we decreased the needed force by half in order to do the same amount of work. The inclined plane is simply a flat surface raised at an angle, like a ramp. According to Bob Williams, a professor in the department of mechanical engineering at the Russ College of Engineering and Technology at Ohio University, an inclined plane is a way of lifting a load that would be too heavy to lift straight up.