Talha's Physics Academy
Turning Effect of Forces - Torque and Principle of Moments
Q.6 Define Torque, its formula and unit. Also write factors affecting torque.
Torque (Moment of Force)
"The turning effect of a force about an axis of rotation is called the moment of force or torque."
Figure: Demonstration of torque produced by a force acting at a perpendicular distance (moment arm) from the axis of rotation.
Factors on Which Torque Depends
- The Magnitude of the Applied Force ($F$): A larger force produces a greater turning effect.
- The Perpendicular Distance / Moment Arm ($l$): The distance between the axis of rotation and the point of application of the force. Longer moment arms make it easier to rotate objects.
Formula
Torque ($\tau$) is mathematically expressed as the product of force and the moment arm:
$\tau = \text{Force} \times \text{Moment Arm} \implies \tau = F \times l$
SI Unit
The SI unit of torque is newton-meter ($\text{N}\cdot\text{m}$).
Q.7 State Principle of Moment with example.
Principle of Moments
"The sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about that same point for a body in rotational equilibrium."
When the sum of all the clockwise moments acting on a body is perfectly balanced by the sum of all the anticlockwise moments, the body satisfies the principle of moments and remains in rotational equilibrium.
$\sum \tau_{\text{clockwise}} = \sum \tau_{\text{anticlockwise}}$
Example:
Consider two children playing on a see-saw. Mirha is sitting on the right side and Arwa is sitting on the left side of the central pivot. When the clockwise turning effect produced by Mirha equals the anticlockwise turning effect produced by Arwa, the see-saw balances horizontally. In this balanced condition, neither side moves up or down.
Consider two children playing on a see-saw. Mirha is sitting on the right side and Arwa is sitting on the left side of the central pivot. When the clockwise turning effect produced by Mirha equals the anticlockwise turning effect produced by Arwa, the see-saw balances horizontally. In this balanced condition, neither side moves up or down.
Figure: Demonstration of Principle of Moment where two children balancing on a see saw.
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