Turning effect of forces

Class 9 · Physics · 6 questions

Name: ____________________ Date: ____________

The turning effect of a force about a point is called:
- A Torque
- B Power
- C Pressure
- D Momentum
A force of 10 N acts at a perpendicular distance of 0.5 m from a pivot. What is the torque?
- A 10.5 N m
- B 5 N m
- C 20 N m
- D 0.05 N m
For a body to be in equilibrium, the resultant force and resultant torque must be:
- A Infinite
- B Equal to the weight
- C Zero
- D Maximum
The centre of gravity of a uniform metre rule lies at the:
- A 25 cm mark
- B 0 cm mark
- C 50 cm mark
- D 100 cm mark
Two equal and opposite parallel forces that do not act along the same line form a:
- A Lever
- B Moment arm
- C Couple
- D Resultant
A body is more stable when its centre of gravity is:
- A Lower and its base wide
- B Higher and its base narrow
- C Outside the body
- D At the top

Answer key

1. A, 2. B, 3. C, 4. C, 5. C, 6. A

Torque, or moment of force, measures the turning effect of a force.
Torque = force x perpendicular distance = 10 x 0.5 = 5 N m.
Both the net force and the net torque must be zero for equilibrium.
For a uniform rod the centre of gravity is at its middle, the 50 cm mark.
Such a pair of forces is called a couple and produces rotation without translation.
A low centre of gravity and a wide base make it harder to topple.