What’s the parallel axis theorem?

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The parallel axis theorem determines the moment of inertia of an object as it rotates about any axis. It applies to any solid object in rotation, including irregular shapes. The moment of inertia is the resistance of an object to change in speed or direction of rotation. For regular objects, the moment of inertia can be solved using simple formulas specific to the shape of these objects. For irregular shapes, the moment of inertia can be solved using calculus. The minimum amount of force required to change an object’s speed or direction relative to its center of mass is its moment of inertia. The parallel axis theorem formula holds for any rigid body that rotates about an axis.

The parallel axis theorem is used in physics to determine the moment of inertia of an object as it rotates about any axis. The theorem states that there is a relationship between the inertia of an object rotating about its center of gravity and an axis parallel to this center. This theorem applies to any solid object in rotation, including irregular shapes.

The resistance of an object to change in speed or direction of rotation in terms of inertia is measured by the parallel axis theorem. Inertia is the resistance that a physical object exhibits to a change in its state of motion. When an object moves in a linear direction, this resistance is represented by the mass of an object. In rotational dynamics, when describing angular momentum, angular velocity, torque, and angular acceleration, this resistance is called the moment of inertia.

For regular objects, such as spheres, rods, and cylinders, the moment of inertia can be solved using simple formulas specific to the shape of these objects. For irregular shapes, the moment of inertia can be solved using calculus, which allows for the use of continuous variables. In an irregular shape, rotation of the object about an axis results in a continuous distribution of mass. In an object that is not symmetrical, the mass will not be distributed uniformly as it rotates, meaning that solving its moment of inertia will require the use of multiple variables. The moment of inertia is a variable in the equation of the parallel axis theorem.

The minimum amount of force required to change an object’s speed or direction relative to its center of mass is its moment of inertia. The center of mass, also known as the center of gravity, is the point in an object where mass is balanced equally on all sides. For example, a seesaw will have a center of gravity in the center of the board, which can be demonstrated by balancing the board on a pivot point in the center. If an adult and a child are placed at opposite ends of the circular saw, the center of mass will move towards the adult, until the total mass is equal on both sides.

In the parallel axis theorem, the moment of inertia for any axis parallel to the axis in the center of mass can be given with a single formula. The inertia of the parallel axis equals the inertia of the center of mass plus the point mass of the object multiplied by the square of the distance between the center of mass and the parallel axis. This formula holds for any rigid body that rotates about an axis.




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