9702 · 4.1
Turning effects of forces flashcards
Revision flashcards for Cambridge 9702 Turning effects of forces (syllabus 4.1). Flip, recall, then mark a real past-paper question.
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What is the Centre of Gravity (CoG)?
The single point where an object's entire weight appears to act.
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How is the moment of a force calculated?
Force multiplied by the perpendicular distance from its line of action to the pivot.
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What defines a 'couple' in physics?
Two forces that are equal in magnitude, opposite in direction, parallel, and act along different lines.
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State the Principle of Moments.
For rotational equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments about the same point.
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What are the two conditions for complete equilibrium?
The resultant force and the resultant moment acting on the object must both be zero.
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When do CoG and Centre of Mass (CoM) coincide?
In a uniform gravitational field, CoG and CoM are located at the same point.
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What is the unit for moment and torque?
Newton-metre (Nm).
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How is the torque of a couple calculated?
The magnitude of one force multiplied by the perpendicular distance between the lines of action of the two forces.
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Why is perpendicular distance crucial for moments?
Only the component of the force perpendicular to the distance from the pivot contributes to the turning effect. Using the perpendicular distance ensures the maximum effect is considered directly.
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How can the stability of an object be increased?
By lowering its centre of gravity and/or increasing the area of its base.
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What is the difference between moment and torque?
A moment is the turning effect of a single force about a pivot. Torque is the turning effect of a couple and is independent of any pivot point.
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A force is applied at an angle to a lever. How do you calculate the moment?
Use the component of the force that is perpendicular to the lever, or multiply the full force by the perpendicular distance from the pivot to the line of action of the force.
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What are the three types of equilibrium?
Stable, unstable, and neutral equilibrium.