The point of contraflexure is a point on a beam where the bending moment changes sign from positive to negative or vice versa. This means that the moment changes direction at this point.

Explanation:

- Bending moment: Bending moment is the internal moment that is generated in a beam due to the external load acting on it. It is responsible for the curvature or deflection of a beam. The bending moment varies along the length of the beam and is maximum at the points where the shear force is zero.

- Shear force: Shear force is the internal force that is generated in a beam due to the external load acting on it. It is responsible for the sideways or transverse forces acting on a beam. The shear force also varies along the length of the beam and is maximum at the points where the bending moment changes sign.

- Contraflexure: Contraflexure is the point on a beam where the bending moment changes sign. It is a rare phenomenon that occurs in a beam subjected to a combination of loads.

- Sign convention: The sign convention for bending moment is positive when the moment is causing the beam to sag or deflect downwards and negative when the moment is causing the beam to hog or deflect upwards. The sign convention for shear force is positive when the force is acting upwards and negative when the force is acting downwards.

- Point of contraflexure: The point of contraflexure is the point on a beam where the bending moment changes sign from positive to negative or vice versa. At this point, the bending moment is zero and the shear force is maximum.

In conclusion, the point of contraflexure is a point on a beam where the bending moment changes sign. It is a rare phenomenon that occurs in a beam subjected to a combination of loads. At this point, the bending moment is zero and the shear force is maximum.