The simplest machine, and perhaps the most familiar one, is the lever. A seesaw is a familiar example of a lever, with two people sitting on either end of a board and a pivoting point in the middle. There are three basic parts in all levers.
They are the fulcrum “F,” a force or effort “E,” and a resistance “R.” Shown in Figure 3-7 are the pivot point “F” (fulcrum), the effort “E” which is applied at a distance “L” from the fulcrum, and a resistance “R” which acts at a distance “l” from the fulcrum.
Distances “L” and “l” are the lever arms.
Figure 3-7. First class lever.
The concept of torque was discussed earlier in this chapter, and torque is very much involved in the operation of a lever. When a person sits on one end of a seesaw, that person applies a downward force in pounds which acts along the distance to the center of the seesaw. This combination of force and distance creates torque, which tries to cause rotation.
First Class Lever
In the first class lever, the fulcrum is located between the effort and the resistance. As mentioned earlier, the seesaw is a good example of a lever, and it happens to be a first class lever. The amount of weight and the distance from the fulcrum can be varied to suit the need.
Increasing the distance from the applied effort to the fulcrum, compared to the distance from the fulcrum to the weight being moved, increases the advantage provided by the lever. Crowbars, shears, and pliers are common examples of this class of lever.
The proper balance of an airplane is also a good example, with the center of lift on the wing being the pivot point (fulcrum) and the weight fore and aft of this point being the effort and the resistance.
When calculating how much effort is required to lift a specific weight, or how much weight can be lifted by a specific effort, the following formula can be used.
Effort (E) × Effort Arm (L) = Resistance (R) × Resistance Arm (l)
What this formula really shows is the input torque (effort times effort arm) equals the output torque (resistance times resistance arm). This formula and concept apply to all three classes of levers, and to all simple machines in general.
Example: A first class lever is to be used to lift a 500-lb weight. The distance from the weight to the fulcrum is 12 inches and from the fulcrum to the applied effort is 60 inches. How much force is required to lift the weight?
- The mechanical advantage of the lever in this example would be:
An interesting thing to note with this example lever is if the applied effort moved down 10 inches, the weight on the other end would only move up 2 inches.
The weight being lifted would only move one-fifth as far. The reason for this is the concept of work.
Because a lever cannot have more work output than input, if it allows you to lift 5 times more weight, you will only move it 1⁄5 as far as you move the effort.
Second Class Lever
The second class lever has the fulcrum at one end and the effort is applied at the other end. The resistance is somewhere between these points. A wheelbarrow is a good example of a second class lever, with the wheel at one end being the fulcrum, the handles at the opposite end being the applied effort, and the bucket in the middle being where the weight or resistance is placed. [Figure 3-8]
Figure 3-8. Second class lever.
Both first and second class levers are commonly used to help in overcoming big resistances with a relatively small effort. The first class lever, however, is more versatile.
Depending on how close or how far away the weight is placed from the fulcrum, the first class lever can be made to gain force or gain distance, but not both at the same time.
The second class lever can only be made to gain force.
Example: The distance from the center of the wheel to the handles on a wheelbarrow is 60 inches. The weight in the bucket is 18 inches from the center of the wheel. If 300 lb is placed in the bucket, how much force must be applied at the handles to lift the wheelbarrow?
- The mechanical advantage of the lever in this example would be:
- Third Class Lever
There are occasions when it is desirable to speed up the movement of the resistance even though a large amount of effort must be used. Levers that help accomplish this are third class levers.
As shown in Figure 3-9, the fulcrum is at one end of the lever and the weight or resistance to be overcome is at the other end, with the effort applied at some point between. Third class levers are easily recognized because the effort is applied between the fulcrum and the resistance.
The retractable main landing gear on an airplane is a good example of a third class lever. The top of the landing gear, where it attaches to the airplane, is the pivot point. The wheel and brake assembly at the bottom of the landing gear is the resistance.
The hydraulic actuator that makes the gear retract is attached somewhere in the middle, and that is the applied effort.
Figure 3-9. Third class lever.
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Teaching Simple Machines
Background on Simple Machines:
A machine is a device that does work. Most machines consist of a number of elements, such as gears and ball bearings, that work together in a complex way. Nonetheless, no matter how complex they are, all machines are based in some way on six types of simple machines. These six types of machines are the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw.
Principles of Simple Machines: Machines simply transmit mechanical work from one part of a device to another part. A machine produces force and controls the direction and the motion of force, but it cannot create energy. A machine's ability to do work is measured by two factors. These are (1) mechanical advantage and (2) efficiency.
Mechanical advantage. In machines that transmit only mechanical energy, the ratio of the force exerted by the machine to the force applied to the machine is known as mechanical advantage.
Under mechanical advantage the distance the load will be moved will be only be a fraction of the distance through which the effort is applied. While machines can provide a mechanical advantage of greater than 1.0 (and even less than 1.
0 if desired), no machine can never do more mechanical work than the mechanical work put into it.
Efficiency. The efficiency of a machine is the ratio between the work it supplies and the work put into it. Although friction can be decreased by oiling any sliding or rotating parts, all machines produce some friction.
A lever has a high efficiency due to the fact that it has low internal resistance. The work it puts out is almost equal to the work it receives, because energy used up by friction is quite small.
On the other hand, an a pulley might be relatively inefficient due to a considerably greater amount of internal friction. Simple machines always have efficiencies of less than 1.0 due to internal friction. Energy conservation.
Ignoring for a moment the losses of energy due to friction, the work done on a simple machine is the same as the work done by the machine to perform some sort of task. If work in equals work out, then the machine is 100% efficient.
Lever. A lever is a bar resting on a pivot. Force (effort) applied at one point is transmitted across the pivot (fulcrum) to another point which moves an object (load).
The ideal mechanical advantage (IMA) – ignoring internal friction – of a lever depends on the ratio of the length of the lever arm where the force is applied divided by the length of the lever are that lifts the load. The IMA of a lever can be less than or greater than 1 depending on the class of the lever. There are three classes of levers, depending on the relative positions of the effort is applied, load, and fulcrum.
- First-class levers have the fulcrum located between the load and the effort (LFE). If the two arms of the lever are of equal length, the effort must be equal to the load. To lift 10 pounds, an effort of 10 pounds must be used. If the effort arm is longer than the load arm, as with a crowbar, the hand applying the effort travels farther and the effort is less than the load. SOCIAL CONTEXT: Seesaws, crowbars, and equal-arm balances are examples of a first class lever; a pair of scissors is a double lever of the first class.
- Second-class levers have the load located between the fulcrum and the effort (FLE). As in a wheel barrow, the axle of the wheel is the fulcrum, the handles represent the position where the effort is applied, and the load is placed between the hands and the axle. The hands applying the effort travel a greater distance and is less than the load. SOCIAL CONTEXT: In addition to a wheelbarrow, a pry bar represents a second-class lever. A nutcracker is a double lever of this class.
- Third-class levers have the effort located between the load and the fulcrum (FEL). The hand applying the effort always travels a shorter distance and must be greater than the load. SOCIAL CONTEXT: The forearm is a third-class lever. The hand holding the weight is lifted by the bicep muscles of the upper arm that is attached to the forearm near the elbow. The elbow joint is the fulcrum.
- Compound levers combine two or more levers, usually to decrease the effort. By applying the principle of the compound lever, a person could use the weight of one hand to balance a load weighing a ton.
- Law of Equilibrium A lever is in equilibrium when the effort and the load balance each other; that is, the sum of the torques (force times lever arm) equals zero. The effort multiplied by the length of the effort arm equals the load multiplied by the length of the load arm.
Wheel and axle. The wheel and axle is essentially a modified lever, but it can move a load farther than a lever can. The center of the axle serves as a fulcrum.
The ideal mechanical advantage (IMA) of a wheel and axle is the ratio of the radii. If the effort is applied to the large radius, the mechanical advantage is R/r which will be more than one; if the effort is applied to the small radius, the mechanical advantage is still R/r, but it will be less than 1.
Pulley. A pulley is a wheel over which a rope or belt is passed. It is also a form of the wheel and axle. Pulleys are often interconnected in order to obtain considerable mechanical advantage.
The ideal mechanical advantage (IMA) of a pulley is directly dependent upon the number of support strings, N.
How to Make a Lever – Simple Machine Science Lesson & Project
Simple machines make work easier by multiplying, reducing, or changing the direction of a force.
There are six different types of simple machines, including ramps, levers, and gears.
Simple Machines Science Projects
Make a Lever
A lever is a type of simple machine. You can make one and experiment with how moving the pivot point, or fulcrum, changes the way the lever can lift things.
What You Need:
- A sturdy wooden ruler, piece of foam board, or thin piece of wood (we used a 24” piece of basswood, which can be purchased at a craft store)
- A large binder clip
- Weights or variety of objects (or small paper cups and pennies to use as weights)
What You Do:
- Remove the metal clips from the base of the binder clip by squeezing the sides together and fitting the ends through the groove.
- Set the lever (ruler, foam board, or wood) over the binder clip. Position it near the middle so that the board is balanced. The binder clip is called the fulcrum, which gives your lever a pivot point.
- Place a weight on one end and note what happens to each end of the lever.
- Move the fulcrum (binder clip) closer to the end with the weight.
- Place a lighter weight or object on the other end. If nothing happens, adjust the position of the binder clip (fulcrum) until the heavier end is raised up.
- You have just made a lever and used it to lift a heavy object with a lighter one!
- You can experiment more by moving the fulcrum and changing the placement of the weights.
In this experiment, you took a basic ruler or piece of wood and added a fulcrum to make a simple machine called a lever!
To understand how a lever works – picture a playground see-saw. With the heavier object on one end, the lighter (empty) end of the lever was raised up.
By moving the fulcrum closer to the heavy end, you were able to use the lever to help you raise the heavier object when you placed a lighter one on the opposite end.
This didn’t change anything about the lighter weight – it stayed exactly the same. Moving the lever’s pivot point closer to the object you were trying to lift changed how much force (or work) it took to lift the object. Moving the fulcrum closer to the object made it much easier to lift a heavy object.
What do you think would happen if you moved the fulcrum the opposite direction? It would take more force, or in this example, a heavier weight to lift the object!
When talking about levers, things can get a little confusing, so there are a few terms we can use to help keep things straight.
In our experiment above, the heavy object we were trying to lift is called the load force.
The lighter weight we used to lift the load force is called the effort force. When the fulcrum was in the middle of the lever, the effort force had to be greater than the load force in order to lift the load force up.
- But, by simply changing the pivot point of the lever, we were able to use a smaller effort force to lift the greater load force.
- That is the beauty of levers – making work easier by lowering the amount of force that is required to lift or move something!
- For further study, try these:
- Simple machines science projects
Simple Machines Science Lesson
Introduction to Simple Machines
- Simple machines make work easier by multiplying, reducing, or changing the direction of a force.
- The scientific formula for work is w = f x d, or, work is equal to force multiplied by distance.
- Simple machines cannot change the amount of work done, but they can reduce the effort force that is required to do the work!
- As you can see by this formula, if the effort force is reduced, distance is increased.
There are six types of simple machines: pulleys, wheels and axles, inclined planes, levers, wedges, and screws. Wedges and screws are both a type of inclined plane; pulleys and wheels and axles are both a form of lever.
An inclined plane is a board or other flat surface set at an angle to the horizontal. Since the force needed to push an object up an inclined plane is less than the force needed to lift the same object, inclined planes reduce the amount of force necessary to do a job. A ramp is an example of an inclined plane.
What is a lever simple machine
A lever is simply a plank or ridged beam that is free to rotate on a pivot. It is perfect for lifting or moving heavy things. It is a very useful simple machine, and you can find them everywhere. Good examples of levers include the seesaw, crowbar, fishing-line, oars, wheelbarrows and the garden shovel.
Parts of a lever Levers have four very important parts — the bar or beam, the fulcrum (the pivot or the turning point), effort (or force) and the load.
The beam is simply a long plank. It may be wood, metal or any durable material. The beam rests on a fulcrum (a point on the bar creating a pivot).
When you push down one end of a lever, you apply a force (input) to it. The lever pivots on the fulcrum, and produces an output (lift a load) by exerting an output force on the load. A lever makes work easier by both increasing your input force and changing the direction of your input force.
The Three Lever Classes
The parts of the lever are not always in the same arrangement. The load, fulcrum, and effort may be at different places on the plank.
Class One Lever In this class, the Fulcrum is between the Effort and the Load. The mechanical advantage is more if the Load is closer to the fulcrum. Examples of Class One Levers include seesaws, boat oars and crowbar.
Class Two Lever In this class, the Load is between the Effort and the Fulcrum. The mechanical advantage is more if the load is closer to the fulcrum. Examples of Class Two Levers include wheelbarrows.
Class Three Lever In this class, the Effort is between the Load and the Fulcrum. The mechanical advantage is more if the effort is closer to the load. An example of Class Three Lever is a garden shovel.
Experiments focus on addressing areas pertaining to the relationships between effort force, load force, work, and mechanical advantage, such as: how simple machines change the force needed to lift a load; mechanical advantages relation to effort and load forces; how the relationship between the fulcrum, effort and load affect the force needed to lift a load; how mechanical advantage relates to effort and load forces and the length of effort and load arms.
Through investigations and models created with pulleys and levers, students find that work in physical terms is a force applied over a distance.
Students also discover that while a simple machine may make work seem easier, in reality the amount of work does not decrease.
Instead, machines make work seem easier by changing the direction of a force or by providing mechanical advantage as a ratio of load force to effort force.
Students examine how pulleys can be used alone or in combination affect the amount of force needed to lift a load in a bucket.
Students find that a single pulley does not improve mechanical advantage, yet makes the effort applied to the load seem less because the pulley allows the effort to be applied in the direction of the force of gravity rather than against it.
Students also discover that using two pulleys provides a mechanical advantage of 2, but that the effort must be applied over twice the distance in order to gain this mechanical advantage Thus the amount of work done on the load force remains the same.
Students conduct a series of experiments comparing the effects of changing load and effort force distances for the three classes of levers.
Students discover that when the fulcrum is between the load and the effort (first class lever), moving the fulcrum closer to the load increases the length of the effort arm and decreases the length of the load arm.
This change in fulcrum position results in an increase in mechanical advantage by decreasing the amount of effort force needed to lift the load.
Thus, students will discover that mechanical advantage in levers can be determined either as the ratio of load force to effort force, or as the ratio of effort arm length to load arm length. Students then predict and test the effect of moving the fulcrum closer to the effort force. Students find that as the length of the effort arm decreases the amount of effort force required to lift the load increases.
Students explore how the position of the fulcrum and the length of the effort and load arms in a second-class lever affect mechanical advantage. A second-class lever is one in which the load is located between the fulcrum and the effort.
In a second-class lever, moving the load changes the length of the load arm but has no effect on the length of the effort arm.
As the effort arm is always longer than the load arm in this type of lever, mechanical advantage decreases as the length of the load arm approaches the length of the effort arm, yet will always be greater than 1 because the load must be located between the fulcrum and the effort.
Students then discover that the reverse is true when they create a third-class lever by placing the effort between the load and the fulcrum.
Students discover that in the case of a third-class lever the effort arm is always shorter than the load arm, and thus the mechanical advantage will always be less than 1.
Students also create a model of a third-class lever that is part of their daily life by modeling a human arm.
The CELL culminates with a performance assessment that asks students to apply their knowledge of simple machine design and mechanical advantage to create two machines, each with a mechanical advantage greater than 1.3.
In doing so, students will demonstrate their understanding of the relationships between effort force, load force, pulleys, levers, mechanical advantage and work.
The performance assessment will also provide students with an opportunity to hone their problem-solving skills as they test their knowledge.
Through this series of investigations students will come to understand that simple machines make work seem easier by changing the direction of an applied force as well as altering the mechanical advantage by afforded by using the machine.
- Discover that simple machines make work seem easier by changing the force needed to lift a load.
- Learn how effort and load forces affect the mechanical advantage of pulleys and levers.
There are two main families of simple machines – the lever family and the inclined plane family. Just like most families share similar physical or behavioural characteristics, so too do the members of each simple machine family.
We will learn to identify and analyze each family member through a physics lens and learn how each makes our lives easier on a daily basis.
Let’s start with the lever family!
Did you know that you use levers every day? Our entire biomechanical system is made up of many different levers that work together so that we can move heavy objects, bite into our food, and throw a baseball.
A lever is a simple machine used to change the magnitude and the direction of forces. A lever is a rigid body or beam that rotates on a central axis called a fulcrum. An input force called the effort force,
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Levers – Simple Machines for Kids
During our Simple Machines unit, we learned about levers. In this post, I start out talking theory. If you prefer, you can jump to the hands-on science activities for kids age 3 – 6.
Key Concept of Levers
You place a long bar onto a fulcrum (pivot point). You apply force in one direction, and the pivot point re-directs the force in another direction. To lift the load on one end, you may need the same weight, or more weight or less weight on the other end… all depending on where the fulcrum is.
If you’re working with small kids, stick to that basic point, and skip all the details I’m about to give on classes of levers!
There are three classes of lever. A first-class lever has the fulcrum in between the effort and the load (e.g. between you and the weight you’re trying to lift). You push down on one end, and the other raises up.