CLASS 11 PHYSICS

System of Particles and Rotational Motion

Move from single-particle motion to centre of mass and rotation.

Learning objective

Use torque, angular momentum and rotational analogies with linear motion.

State Board to NCERT bridge

From balancing objects to analysing how forces cause turning.

Tamil concept bridge

Rotation-il force mattum alla; axis-irundhu distance-um torque-ai maatrum.

GUIDED LESSON

Learn the chapter step by step

Read one concept, explain it in your own words, then connect it to the formula or situation that follows. Do not try to memorise the chapter as isolated definitions.

The centre of mass is the weighted average position of a system. External force controls its motion just as if total mass were concentrated there.

Tamil support: Rotation-il force mattum alla; axis-irundhu distance-um torque-ai maatrum.

Ask yourself: Can I give one everyday example of centre of mass?

WORKED EXAMPLE

Torque

Given: A 10 N force acts perpendicular to a 0.5 m spanner.

1Use tau = rF sin theta.
2The force is perpendicular, so sin 90 degrees = 1.
3tau = 0.5 x 10 x 1.

Answer: Torque = 5 N m.

FORMULA / FACT BANK

Know what each relationship means

Torque

tau = rF sin theta

Turning effect about an axis.

Angular momentum

L = I omega

For a rigid body about a fixed axis.

Memory cue: centre of mass · moment of inertia · torque · angular momentum

SELF-CHECK

Which concept should you start with?

Choose the core foundation concept for this chapter.

COMMON MISTAKES

Do not use a formula before identifying the physical quantities and their SI units.
Keep direction, sign convention and stated conditions visible throughout a solution.
Check whether your answer has a sensible unit and magnitude.

REVISION PLAN

1. Re-read the visual summary and say each revision target aloud.
2. Redo the worked example without looking at the steps.
3. Complete the 80-question bank and revisit every incorrect explanation.

VISUAL NOTES