---
title: "Governor terms and governor versus flywheel"
subject: "Theory of Mechanism and Machine II"
chapter: 4
key: "semester_7/theory_of_mechanism_and_machine_ii:governor-terms-governor-flywheel"
source: https://www.bctengineer.com/q/semester_7/theory_of_mechanism_and_machine_ii/governor-terms-governor-flywheel
site: BCT Engineering
---

# Governor terms and governor versus flywheel

Theory of Mechanism and Machine II · Chapter 4: Governors

- Asked in: year not given, 6 marks
- Video: [Flywheel and Governor | Difference between Flywheel and Governor | Flywheel Vs Governor (Hindi)](https://www.youtube.com/watch?v=v3qgZT24wZo) — Unique knowledge city
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/theory_of_mechanism_and_machine_ii/governor-terms-governor-flywheel
- Whole chapter: https://www.bctengineer.com/md/semester_7/theory_of_mechanism_and_machine_ii/chapter-4

## Question

Differentiate between a governor and a flywheel. Explain the terms sensitiveness, stability, isochronism, hunting, effort and power of a governor.

## Short answer

A governor controls mean speed by regulating fuel; a flywheel reduces cyclic speed fluctuations by storing kinetic energy. Sensitiveness = (N2-N1)/Nmean. Stability: a single equilibrium radius per speed, increasing with speed. Isochronism: constant equilibrium speed for all radii (unstable). Hunting: oscillation from overcorrection. Effort: mean sleeve force for a given speed change; Power: effort × sleeve lift.

## Answer

#### Governor vs flywheel
| Point | Governor | Flywheel |
|---|---|---|
| Function | Controls the mean speed against load changes over a long period | Reduces speed fluctuation within one cycle |
| Action | Regulates fuel or steam supply | Stores and releases kinetic energy |
| Works on | Changes of load | Changes of torque within a cycle |
| Control | Active, with a sleeve and a link to the throttle | Passive, no control mechanism |
| Needed when | Load varies widely | Torque varies during the cycle |

#### Terms
- **Sensitiveness:** A governor is sensitive if it responds to a small change of speed. It is measured as
$$
\text{Sensitiveness} = \frac{N_2 - N_1}{N} = \frac{2(N_2 - N_1)}{N_1 + N_2}
$$
where $N_1, N_2$ are the minimum and maximum equilibrium speeds and $N$ is the mean speed.
- **Stability:** A governor is stable if, for every speed in its working range, there is only one radius of the balls at which the sleeve is in equilibrium, and the ball radius increases with speed.
- **Isochronism:** The limiting case of a governor whose equilibrium speed is the same for all radii of rotation of the balls. Its range of speed is zero, so it is infinitely sensitive, but it is unstable (the balls move to an extreme position).
- **Hunting:** Continuous fluctuation of the engine speed above and below the mean caused by an over-sensitive governor: it overcorrects, the sleeve moves up and down, and the speed keeps oscillating.
- **Effort:** The mean force exerted at the sleeve for a given fractional change of speed (e.g. 1%). It is the force that can be used to move the control mechanism.
- **Power:** The work done at the sleeve for a given percentage change of speed; power $=$ (mean effort) $\times$ (lift of the sleeve).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which statement correctly distinguishes a governor from a flywheel?
   A. A governor controls mean speed against load changes, a flywheel reduces fluctuation within a cycle
   B. A governor stores energy and a flywheel regulates fuel
   C. Both do the same job in different engines
   D. A flywheel is active and a governor is passive
   Answer: A. Governors regulate fuel supply in response to load changes; flywheels passively store and return kinetic energy within a cycle. (Key point: Governor vs flywheel)

2. Sensitiveness of a governor is measured as:
   A. (N2 - N1)/N, the speed range over mean speed
   B. N/(N2 - N1)
   C. N1/N2
   D. Sleeve lift / ball radius
   Answer: A. It equals (N2-N1)/N = 2(N2-N1)/(N1+N2); more sensitive means smaller speed range for the sleeve to move. (Key point: Sensitiveness)

3. An isochronous governor is one in which:
   A. Equilibrium speed is the same at all ball radii; it is infinitely sensitive but unstable
   B. Equilibrium speed rises with radius
   C. The sleeve never moves
   D. It never hunts and is perfectly stable
   Answer: A. Speed range is zero, so it is infinitely sensitive, but the balls go to an extreme position, so it is unstable. (Key point: Isochronism)

4. Hunting is caused by:
   A. An over-sensitive governor that overcorrects so speed oscillates
   B. A governor with too much friction
   C. A flywheel that is too heavy
   D. A constant load
   Answer: A. An over-sensitive governor makes the sleeve move up and down continuously, so the speed keeps oscillating about the mean. (Key point: Hunting)

5. The power of a governor is:
   A. Mean effort x lift of sleeve
   B. Effort / lift
   C. Sleeve force x ball speed
   D. Centrifugal force x radius
   Answer: A. Power is the work done at the sleeve for a given percentage change of speed = mean effort x lift. (Key point: Power of governor)

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