What causes objects to rotate?

Objects rotate due to the application of a torque or rotational force, which is often caused by an external influence.

In more detail, rotation in physics is a movement that occurs when a force is applied not at the centre of mass of an object, but at a distance from it. This force is known as torque. Torque, also known as the moment of force, is the rotational equivalent of linear force. It is the product of the force and the distance from the point of rotation to the point where the force is applied.

The direction of rotation is determined by the right-hand rule. If you curl the fingers of your right hand in the direction of the force, your thumb will point in the direction of the rotation. This is a fundamental principle in physics known as the right-hand rule.

The amount of rotation depends on the magnitude of the force, the distance from the point of rotation (also known as the moment arm or lever arm), and the angle at which the force is applied. The greater the force or the longer the moment arm, the greater the torque and thus the greater the rotation. Similarly, if the force is applied at a larger angle, the torque will be greater, leading to a larger rotation.

In addition, the rotational inertia or moment of inertia of the object also plays a role. This is a measure of an object's resistance to changes in its rotation. It depends on both the mass of the object and its distribution of mass around the axis of rotation. An object with a high moment of inertia will rotate less for a given torque than an object with a low moment of inertia.

In summary, the rotation of objects is caused by the application of a torque, which is influenced by the force applied, the distance from the point of rotation, the angle of application, and the object's moment of inertia.