Torque and Moments
Torque measures a force's turning effect: τ = rF sin θ.
About this topic
Torque is the turning effect of a force about a pivot: τ = rF sin θ, where r is the distance from the pivot and θ the angle between the force and lever arm. It is measured in newton-metres. A longer wrench or pushing a door far from its hinges makes turning easier.
Balance on a seesaw requires equal clockwise and anticlockwise torques, so a lighter child sits farther from the pivot than a heavier one. The principle of moments states that for rotational equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments. The perpendicular distance from the pivot to the line of action is the lever arm.
Example: a 300 N child sits 1 m from the pivot, so a 200 N child must sit 1.5 m on the other side. A 0.3 m wrench with 100 N applied at a right angle gives 30 N·m. Spanners, screwdrivers, bicycle pedals, wheelbarrows and scissors all rely on torque.
Common errors: using the distance along the force instead of the perpendicular distance, and confusing torque, measured in N·m, with energy, measured in joules.
Key ideas
- Longer lever arm gives more torque
- Seesaws balance when torques match
- Unit: N·m
Quick check
Use cases: where Torque and Moments helps
- Homework: review the key idea behind Torque and Moments before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Torque and Moments without notes.
- Visual learning: play with the interactive lab to see how Torque and Moments changes when you adjust its inputs.
- Teaching a friend: explain Torque and Moments in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Torque and Moments?
Torque measures a force's turning effect: τ = rF sin θ.
What will I learn in Torque and Moments?
Longer lever arm gives more torque. Seesaws balance when torques match. Unit: N·m.
Is Torque and Moments part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Torque and Moments lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Torque and Moments?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.