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Explanation how a Lever is a Simple Machine by Ron Kurtus - Succeed in Understanding Physics. Also refer to mechanical advantage, fulcrum, force, effort, load, weight, classes, physical science, School for Champions. Copyright © Restrictions
Lever is a Simple Machine
by Ron Kurtus (26 June 2008)
A lever is a simple machine that allows you to gain a mechanical advantage in moving an object or in applying a force to an object. It is considered a "pure" simple machine because friction is not a factor to overcome, as in other simple machines.
A lever consists of a fulcrum, applied force and load. There are three common types or classes of levers, depending on where the fulcrum and applied force is located. The mechanical advantage is that you can move a heavy object using less force than the weight of the object, you can propel an object faster by applying a force at a slower speed, or you can move an object further than the distance you apply to the lever.
Questions you may have include:
- What are the parts of a lever?
- What are the three lever classes?
- What are the uses for a lever?
This lesson will answer those questions.
Useful tool: Metric-English Conversion
Parts of a lever
A typical lever consists of a solid board or rod that can pivot about a point or fulcrum. A force or effort is applied, resulting in moving or applying force to a load. The distance from the applied force or effort force to the fulcrum is called the effort arm and the distance from the load to the fulcrum is called the load arm.
Parts of a Lever
Since there is typically a very small amount of friction at the fulcrum, overcoming friction is not a factor in a lever as it might be in another simple machine like a ramp or wedge. Thus, we consider a lever a pure simple machine.
Three lever classes
There are three types or classes of levers, according to where the load and effort are located with respect to the fulcrum.
Class 1
A class 1 lever has the fulcrum placed between the effort and load. The movement of the load is in the opposite direction of the movement of the effort. Note that the length of the effort arm can be greater than, equal to or less than the length of the load arm in a class 1 lever.
Class 1 lever
Examples of class 1 levers include:
- Teeter-totter
- Oars on a boat
- Catapult
- Shoehorn
- Scissors
- Pair of pliers
Double class 1 lever
A scissors and a pair of pliers are considered double class 1 levers.
A pair of pliers is a double class 1 lever
Class 2
A class 2 lever has the load in between the effort and the fulcrum. In this type of lever, the movement of the load is in the same direction as that of the effort. Note that the length of the effort arm goes all the way to the fulcrum and is always greater than the length of the load arm in a class 2 lever.
Class 2 lever
Examples of class 2 levers include:
- Wheelbarrow
- Crowbar
- Nut cracker
Class 3
A class 3 lever has the effort in between the load and the fulcrum. Both the effort and load are in the same direction. Note that the length of the load arm goes all the way to the fulcrum and is always greater than the length of the effort arm in a class 3 lever.
Class 3 lever
Examples of class 3 levers include:
- Tweezers
- Stapler
- Mousetrap
- Broom
- Hockey stick
Uses for a lever
The reason for a lever is that you can use it for a mechanical advantage in lifting heavy loads, moving things a greater distance or increasing the speed of an object.
Increase force
You can increase the applied force in order to lift heavier loads. The relationship between the effort and force on the load is dependent on the ratio of the arms of the lever, according to the equation:
FL= FEE/ L
where
- FE is the effort force
- E is the length of the effort arm
- FL is the load force
- L is the length of the load arm
The force units must be the same and the distance units must be the same. The equation can be stated as: the force of the load equals the force of the effort times the length of the effort arm divided by the length of the load arm.
Example
Thus, if the length of the effort arm in a class 1 lever is 10 meters and the load arm is 1 meter, and you push down with an effort of 2 kilograms, you will be able to lift a load of 20 kilograms. In other words, you can lift up 10 times the force that you push down. Thus would also be true using a class 2 lever, except that you would be pulling up instead of pushing down.
Increase distance moved
A similar equation is used in the case where you want to move an object a greater distance.
dL = dEE/L
where
- dE is the distance the effort force is moved
- dL is the distance the load force is moved
This can be stated as: the distance the load moves equals the distance of the effort moved times the length of the effort arm divided by the length of the load arm.
Increase speed
Likewise, you can increase the speed that an object moves, related to the length of the lever arms.
sL = sEE/L
where
- sE is the speed of the effort
- sL is the resulting speed of the load
This can be stated as: the speed of the load equals the speed of the effort times the length of the effort arm divided by the length of the load arm.
Summary
A lever is a simple machine that allows you to gain a mechanical advantage. It consists of a fulcrum, applied force and load. The three types or classes of levers, depend on where the fulcrum and applied force is located. The mechanical advantage you can gain is to a heavy object using less force than the weight of the object, to propel an object faster by applying a force at a slower speed or to move an object further than the distance you apply to the lever.
Leveraging gives you an advantage
Resources and references
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Top-rated books on Simple Machines
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