Levers
Lever
A rigid bar that pivots on a fulcrum to move a load with an applied effort.
Types of Levers
Levers are classified into three types based on the relative positions of the Load (L), Effort (E), and Fulcrum (F).
- First-Class Levers
- Second-Class Levers
- Third-Class Levers
First-Class Levers
1st-class lever
A lever where the fulcrum is between the effort and the load. For example, a seesaw or a pair of scissors.
- Can increase force or change the direction of force.
- The mechanical advantage depends on the distance between the fulcrum and the effort/load.
- Seesaw: The fulcrum is in the center, with the effort and load on opposite ends.
- Crowbar: Used to lift heavy objects by applying force on one end.
Second-Class Levers
2nd-class lever
A lever where the load is between the effort and the fulcrum. For example, a wheelbarrow.
- Always provide a mechanical advantage (effort is less than the load).
- The effort moves a greater distance than the load.
- Wheelbarrow: The wheel acts as the fulcrum, the load is in the middle, and the effort is applied at the handles.
- Nutcracker: The load (nut) is between the fulcrum (hinge) and the effort (handles).
Second-class levers are ideal for lifting heavy loads with minimal effort, making them efficient for tasks like moving soil or breaking nuts.
Third-Class Levers
3rd-class lever
A lever where the effort is between the fulcrum and the load. For example, tweezers and most human limbs (like your forearm) are 3rd-class levers.
- Do not provide a mechanical advantage (effort is greater than the load).
- Increase the speed and range of motion of the load.
- Fishing Rod: The hand applies effort in the middle, with the fulcrum at the handle and the load (fish) at the end.
- Tweezers: The effort is applied in the middle, with the fulcrum at the joint and the load at the tips.
1st Class: F (Fulcrum) is in the middle → E–F–L
2nd Class: L (Load) is in the middle → F–L–E
3rd Class: E (Effort) is in the middle → F–E–L
Mechanical Advantage and Levers
Mechanical Advantage
The ratio of output force to input force in a mechanical system.
$$\text{MA} = \frac{\text{Load}}{\text{Effort}}$$
- First-Class Levers: MA can be greater than, less than, or equal to 1, depending on the fulcrum's position.
- Second-Class Levers: MA is always greater than 1, making them efficient for lifting heavy loads.
- Third-Class Levers: MA is always less than 1, prioritizing speed and range of motion.
