The middle component determines whether the lever is 1st, 2nd or 3rd class. 1st class levers have fulcrum in the middle, for example, Teeter-totter, scissors and pliers. Out of them, scissors and pliers are considered a double Class 1 levers. In 2nd class levers, the load is in the middle. Examples of this are Wheelbarrow and Nut crackers. In class 3rd lever, the effort is in the middle. Examples are Tweezers, Stapler, Mousetrap etc.
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