Explanation:
In a third-class lever:
- Fulcrum: The pivot point (fulcrum) is at one end of the lever.
- Effort: The force you apply (effort) is applied between the fulcrum and the load.
- Load: The object or resistance you are trying to move (load) is located at the opposite end from the fulcrum.
Mechanical Advantage (MA) Formula:
MA=Load ArmEffort Arm\text{MA} = \frac{\text{Load Arm}}{\text{Effort Arm}}
- Effort Arm: The distance between the point where the effort is applied and the fulcrum.
- Load Arm: The distance between the load and the fulcrum.
Key Points:
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Position of Effort: In a third-class lever, the effort is applied closer to the fulcrum than the load. This means the effort arm is always shorter than the load arm.
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Shorter Effort Arm: Since the effort arm is shorter than the load arm, the ratio of the load arm to the effort arm is less than one.
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MA Less Than One: The mechanical advantage (MA), which is the ratio of the load arm to the effort arm, is therefore always less than one. This indicates that more effort force is required to move the load than the load itself, meaning you do not gain a force advantage.
Example:
- Tweezers: Tweezers are a common example of a third-class lever. The effort is applied in the middle, close to the fulcrum (hinge), and the load is at the end (tips of the tweezers). You must apply a greater force to grip something with the tips of the tweezers than the force exerted by the tweezers on the object.
Summary:
We know that, in the third class lever, an effort lies between a load and a fulcrum. So, effort distance (ED) is never greater than load distance (LD) and so the velocity ratio (VR) is less than one since VR = ideal MA.
So, mechanical advantage (MA) in the third class lever is also less than one and it can never magnify the applied force.
