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📐Mechanical & Machinery Principles · 5 min read

Levers & Simple Machines

Three classes of levers, force calculations, and real-world examples

Lever questions appear frequently on mechanical aptitude tests. You need to identify the class of lever, calculate the force required, and know which arrangement gives the most mechanical advantage. The concepts extend directly to elevator components — brakes, door linkages, and safety mechanisms all use lever principles.

On the Test

The EIAT tests lever class identification and "which requires less force" comparisons without a calculator. The key is identifying what sits in the middle of the three elements — that one fact tells you the class and whether you have a force advantage.

•Identify class by what is in the middle: Fulcrum in the middle = Class 1. Load in the middle = Class 2 (always MA > 1). Effort in the middle = Class 3 (always MA < 1, gains speed).
•Longer effort arm = less force needed. Moving your hand farther from the fulcrum always makes lifting easier.
•Know these cold: crowbar = Class 1, wheelbarrow = Class 2, human forearm lifting a weight = Class 3.
⚠Common trap: Assuming Class 3 levers are always "worse." They trade force for speed and range of motion — a question may ask which lever moves the load faster, not which is easier, making Class 3 the correct answer.

The Three Parts of Every Lever

Every lever has exactly three elements: the fulcrum (pivot point), the effort (where you apply force), and the load (the resistance being overcome). The class of lever is determined by the arrangement of these three elements — specifically, which one is in the middle.

Class 1 — Fulcrum in the Middle

Arrangement: Load — Fulcrum — Effort (or Effort — Fulcrum — Load).

Examples: seesaw, scissors, crow bar, pry bar, pliers.

MA = effort arm ÷ load arm. When effort arm > load arm, MA > 1 (easy to lift heavy things). When they're equal, MA = 1. When effort arm < load arm, MA < 1 (need more force than the load — traded for speed).

Most versatile class — can be designed for any MA.

Class 2 — Load in the Middle

Arrangement: Fulcrum — Load — Effort.

Examples: wheelbarrow, nutcracker, bottle opener, door (hinge is fulcrum, knob is effort, load is wherever you're applying force).

The effort arm is always the full length of the lever; the load arm is always shorter. Therefore Class 2 levers always have MA > 1 — you always have a mechanical advantage.

This makes Class 2 levers ideal for lifting or moving heavy objects with less force.

Class 3 — Effort in the Middle

Arrangement: Fulcrum — Effort — Load.

Examples: tweezers, fishing rod, human forearm lifting an object, baseball bat swing.

The effort arm is always shorter than the load arm. Therefore MA < 1 — you always need more force than the load. The trade-off is that small effort movement produces large load movement — you gain speed and range of motion.

The human arm is a Class 3 lever by design — muscles attach close to the joint (fulcrum), giving MA < 1 but allowing fast, wide-range movement of the hand.

Calculating Lever Force

MA = effort arm length ÷ load arm length.

Effort needed = Load ÷ MA, or equivalently: Load × (load arm ÷ effort arm).

Balance principle (moments): Load × load arm = Effort × effort arm. Both sides must be equal for the lever to be in equilibrium.

Example: A 300 lb load sits 2 ft from the fulcrum. What force is needed 8 ft from the fulcrum on the other side? MA = 8 ÷ 2 = 4. Effort = 300 ÷ 4 = 75 lbs.

Inclined Plane & Wedge

Inclined plane (ramp): MA = slope length ÷ vertical height. A 10 ft ramp rising 2 ft: MA = 5. A 500 lb object needs only 100 lbs of push up the ramp — but you push it 10 ft instead of lifting it 2 ft.

Wedge: Two inclined planes back-to-back. MA = length ÷ thickness. Thin wedges have high MA and cut or split more easily. Knives, chisels, and doorstops are all wedges.

Screw: An inclined plane wrapped around a cylinder. One full rotation advances the screw by one pitch (distance between threads). High MA, self-locking — the same reason worm gears are self-locking.

Key Takeaways

✓Identify the class by what's in the middle: Fulcrum → Class 1. Load → Class 2. Effort → Class 3.
✓Class 2 always has MA > 1. Class 3 always has MA < 1.
✓Effort = Load × (load arm ÷ effort arm). Longer effort arm = less force needed.
✓A longer wrench handle gives more MA on a bolt — that's a lever (Class 1).
✓Ramp MA = slope length ÷ height. A shallow ramp is easier to push up.

Key Terms

Fulcrum

The fixed pivot point of a lever.

Effort

The input force applied to the lever.

Load

The resistance or weight being overcome.

Effort arm

Distance from the fulcrum to where effort is applied.

Load arm

Distance from the fulcrum to where the load acts.

Class 1 lever

Fulcrum between effort and load. Examples: crow bar, scissors, seesaw.

Class 2 lever

Load between fulcrum and effort. Always MA > 1. Examples: wheelbarrow, bottle opener.

Class 3 lever

Effort between fulcrum and load. Always MA < 1. Examples: tweezers, fishing rod.

Moment

Turning force = Force × distance from pivot. Moments must balance for equilibrium.

Inclined plane

A ramp. MA = slope length ÷ height.

Pitch

Distance between threads on a screw; determines how far it advances per turn.

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