Simulation · Physics · Class 11
Ladder against a smooth wall
From the lesson Equilibrium of a rigid body in System of Particles and Rotational Motion. Change the values and watch what happens.
Ladder against a smooth wallPhysics · Class 11
The idea behind it
NCERT §6.8
- A rigid body is in mechanical equilibrium when neither its linear momentum nor its angular momentum changes: it has no linear and no angular acceleration.
- Translational equilibrium: ΣF = 0. Rotational equilibrium: Στ = 0. Each is three scalar equations, six conditions in all.
- If all the forces lie in one plane, three conditions are enough: force components add to zero along two perpendicular directions in the plane, and torques about an axis perpendicular to the plane add to zero.
- If ΣF = 0, the total torque is the same about every point, so the origin for torques can be chosen freely.
- Partial equilibrium is possible. Two equal parallel forces in the same direction at the ends of a light rod: zero net torque about the centre but a net force. Equal and opposite forces at the two ends: zero net force but a net torque.
- A couple is a pair of equal and opposite forces with different lines of action. It produces rotation without translation. Turning a bottle lid and a compass needle in the earth's magnetic field (not pointing north–south) are examples.
- The moment of a couple is AB × F, where AB joins the points of application; it does not depend on the point about which moments are taken.
- A particle can only be in translational equilibrium; the forces on it act at one point, so they are concurrent.