Final answer:
Levers are categorized as 1st, 2nd, or 3rd class based on the positions of the fulcrum, input force, and output force. 1st class levers have the fulcrum in the middle; 2nd class levers have the output force in the middle; and 3rd class levers have the input force in the middle.
Step-by-step explanation:
Characteristics of Levers by Class
The characteristics that distinguish levers as 1st class, 2nd class, or 3rd class are defined by the positions of the input force, output force, and the fulcrum (pivot). In all types of levers, only three forces are involved: the input force, the output force, and the force on the fulcrum.
1st class levers have the fulcrum located between the input force and the output force. Classic examples include seesaws and scissors, where the fulcrum is in the middle, the effort is applied on one end, and the resistance or load is on the opposite end.
2nd class levers have the output force located between the fulcrum and the input force, where the load is closer to the fulcrum, and the effort is applied further from the fulcrum. Examples of 2nd class levers include wheelbarrows and nutcrackers. This setup typically results in a small input force moving a large load over a short distance.
3rd class levers have the input force located between the fulcrum and the output force. In this type of lever, the input force acts closer to the fulcrum than the load. For example, a shovel acts as a 3rd class lever when the effort (input force) is applied between the fulcrum (your hand holding the shovel still) and the load (the material being lifted).
The concept of mechanical advantage (MA) is important to understand levers. It describes how much the force is multiplied by the lever. The distances from the fulcrum to the input and output forces are used to calculate the MA. In general terms, a lever with a longer handle will allow the exertion of a greater force due to its larger mechanical advantage.