IB MYP 4-5 Physics- Turning effects of forces- Study Notes - New Syllabus
IB MYP 4-5 Physics-Turning effects of forces- Study Notes
Key Concepts
- Turning effects of forces
Turning Effects of Forces (Moment of Force)
Turning Effects of Forces (Moment of Force)
The turning effect of a force about a point or axis is called the moment of force or torque. It measures how much a force causes an object to rotate.
Formula:
\(\text{Moment of Force (Torque)} = F \times d\)
Where \(F\) = applied force (N) and \(d\) = perpendicular distance from pivot (m)
Conditions for Rotational Equilibrium:
- The sum of clockwise moments = The sum of anticlockwise moments
- Object is not rotating or rotating at constant angular velocity
Principle of Moments:
For a body in equilibrium: \(\sum \text{Clockwise Moments} = \sum \text{Anticlockwise Moments}\)
Turning Effects in Everyday Applications:
- Door Handles: Placed far from hinges to maximize perpendicular distance and reduce force needed.
- Spanners/Wrenches: Longer handle increases torque, making it easier to loosen bolts.
- Oars of a Boat: Force applied far from the pivot (oarlock) increases turning effect in water.
- Steering Wheels: Larger wheel radius means less force is required to turn the vehicle.
- Seesaws: Balancing is based on equal moments on each side of the pivot.
Example:
A force of \(50\ \text{N}\) is applied perpendicular to a spanner of length \(0.3\ \text{m}\). Calculate the moment of force.
▶️ Answer/Explanation
Given: \(F = 50\ \text{N}\), \(d = 0.3\ \text{m}\)
Moment = \(F \times d = 50 \times 0.3 = 15\ \text{Nm}\)
\(\boxed{15\ \text{Nm}}\)
Example:
A seesaw is \(4\ \text{m}\) long with the pivot at the center. A child of weight \(300\ \text{N}\) sits \(1.5\ \text{m}\) from the pivot on one side. Where must a child of weight \(400\ \text{N}\) sit on the other side to balance the seesaw?
▶️ Answer/Explanation
Clockwise moment: \(300 \times 1.5 = 450\ \text{Nm}\)
Let \(d\) be the distance for the \(400\ \text{N}\) child:
Anticlockwise moment: \(400 \times d = 450\)
\(d = \dfrac{450}{400} = 1.125\ \text{m}\)
\(\boxed{1.125\ \text{m from pivot}}\)