Edexcel A Level (IAL) Physics-1.15 Moments- Study Notes- New Syllabus
Edexcel A Level (IAL) Physics -1.15 Moments- Study Notes- New syllabus
Edexcel A Level (IAL) Physics -1.15 Moments- Study Notes -Edexcel A level Physics – per latest Syllabus.
Key Concepts:
- 1.15 be able to use the equation for the moment of a force, moment of force = Fx where x is the perpendicular distance between the line of action of the force and the axis of rotation
Moment of a Force \( \text{Moment} = F x \)
Definition of the Moment of a Force
The moment of a force (also called turning effect) is defined as the product of the force and the perpendicular distance between the line of action of the force and the axis of rotation.
\( \text{Moment} = F x \)
- \( F \) = force applied (N)
- \( x \) = perpendicular distance from pivot to line of action of the force (m)
- Unit of moment: \( \mathrm{N\,m} \)
Key Points:
- A moment causes an object to rotate about a pivot.
- The larger the distance from the pivot, the larger the moment for the same force.
- If the distance is doubled, the moment doubles.
- A force acting directly through the pivot produces zero moment → no turning effect.
- Clockwise and anticlockwise moments are taken with opposite signs.
Perpendicular Distance Matters
Only the perpendicular component contributes to the moment.
If the force is at an angle \( \theta \): \( \text{Moment} = F x \sin\theta \)
Example (Easy)
A force of \( 10\, \mathrm{N} \) acts at a perpendicular distance of \( 0.3\, \mathrm{m} \) from a pivot. Find the moment.
▶️ Answer / Explanation
\( \text{Moment} = F x = 10 \times 0.3 = 3\, \mathrm{N\,m} \)
Example (Medium)
A \( 25\, \mathrm{N} \) force acts at an angle of \( 60^\circ \) to a spanner, whose length is \( 0.20\, \mathrm{m} \). Calculate the moment.
▶️ Answer / Explanation
The perpendicular component is \( F \sin\theta \).
\( \text{Moment} = F x \sin\theta = 25 \times 0.20 \times \sin60^\circ \)
\( = 25 \times 0.20 \times 0.866 = 4.33\, \mathrm{N\,m} \)
Example (Hard)
A uniform beam is pivoted at one end. A \( 50\, \mathrm{N} \) force is applied \( 0.80\, \mathrm{m} \) from the pivot at an angle of \( 30^\circ \) to the beam. Find the moment about the pivot.
▶️ Answer / Explanation
Use the perpendicular component: \( F \sin\theta \).
\( \text{Moment} = F x \sin\theta \)
\( = 50 \times 0.80 \times \sin30^\circ = 50 \times 0.80 \times 0.5 \)
\( = 20\, \mathrm{N\,m} \)