Flywheel
A flywheel is a rotating mechanical device that stores rotational kinetic energy by virtue of its high moment of inertia, acting as an energy reservoir that resists changes in rotational speed. It smooths out fluctuations in power delivery from reciprocating engines (such as internal combustion engines) by absorbing energy during power strokes and releasing it during non-power strokes. Flywheels are used in punch presses, steam engines, automotive engines, and modern grid-scale energy storage systems.
Key Formula
E = (1/2) * I * omega^2
LaTeX: E = \frac{1}{2} I \omega^2
| Symbol | Meaning | Unit |
|---|---|---|
| E | Rotational kinetic energy stored | J (Joules) |
| I | Moment of inertia of flywheel | kg·m² |
| \omega | Angular velocity | rad/s |
Worked Example
Problem
A solid disk flywheel has mass 50 kg and radius 0.4 m. It spins at 3000 rpm. Calculate the kinetic energy stored. (For a solid disk, I = ½MR²)
Solution
Step 1: Convert rpm to rad/s. ω = 3000 × (2π/60) = 3000 × 0.10472 = 314.16 rad/s Step 2: Calculate moment of inertia. I = ½ × M × R² = 0.5 × 50 × (0.4)² = 0.5 × 50 × 0.16 = 4 kg·m² Step 3: Calculate stored energy. E = ½ × I × ω² = 0.5 × 4 × (314.16)² = 2 × 98,696.5 = 197,393 J
Answer
Energy stored = 197.4 kJ ≈ 197 kJ
Flywheel Energy Storage Comparison for Different Applications
| Application | Mass (kg) | Radius (m) | Speed (rpm) | Energy Stored (kJ) |
|---|---|---|---|---|
| Automobile engine flywheel | 5–15 | 0.15–0.20 | 500–5000 | 0.5–10 |
| Industrial punch press | 50–500 | 0.3–0.8 | 100–600 | 10–500 |
| Steam engine flywheel | 100–5000 | 0.5–2.0 | 60–300 | 50–2000 |
| Grid-scale flywheel (steel) | 1000–6000 | 0.5–1.0 | 3000–10000 | 500–30,000 |
| Advanced composite flywheel | 100–400 | 0.3–0.5 | 20,000–60,000 | 1000–100,000 |
Interactive Tools
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Related Terms
Mechanical Clutch
A mechanical clutch is a device that engages and disengages the transmission of power between two rotating shafts, allowing controlled connection and disconnection of a driver and driven component. Clutches are essential in automotive manual transmissions, industrial machinery, and any system requiring selective power coupling without stopping the prime mover. The torque transmission capacity depends on friction surface area, clamping force, and coefficient of friction between the mating surfaces.
Mechanical Gear
A mechanical gear is a rotating machine element with teeth that mesh with another toothed component to transmit torque and rotational motion, simultaneously changing speed and mechanical advantage. Gears are fundamental power transmission devices used to increase or decrease rotational speed, multiply torque, or change the direction of motion. They are ubiquitous in automobiles, industrial machinery, watches, and robotics.
Piston
A piston is a cylindrical mechanical component that reciprocates within a cylinder to transfer force from an expanding gas or fluid to a crankshaft (in engines) or to compress/displace a fluid (in pumps and compressors). The piston forms a movable seal with the cylinder walls through piston rings, enabling controlled pressure differentials. Pistons are the heart of internal combustion engines, steam engines, hydraulic actuators, and pneumatic cylinders.
From Old English "fleogan" (to fly) + "wheel," describing a wheel that spins freely. The flywheel concept was employed in ancient potter's wheels and millstones; James Watt significantly advanced its engineering application in his steam engine designs around 1782–1788 to achieve smoother rotational output.