Will a spinning body continue to spin in the absence of external force??

Question

According to newtons first law of motion, a body continues to move in a straight line with constant velocity until and unless an unbalanced force acts on it..Can this be applied to rotating bodies?..Those that are rotating about an axis...for example a ball rotating about an axis through its center?..Plz help..with detailed explanation

Answer 1

I would reccomend watching videos of a guy named "desertphile" on youtube as thisis one of the things he talks about when arguing with "free energy" or "magnetic motor" cult members.

Answer 2

Yes it will.  Newton's laws of motion were written for linear motion.  There is an equivalent set of laws for rotational motion, in which F = m*a is replace by T = I*α where T is torque, I is moment of inertia, and α is angular acceleration.  In the absence of external force (torque), α is zero, and α is the change in angular velocity.  Therefore the rotational velocity (angular velocity) cannot change in the absence of external torque.

Answer 3

Yes, a spinning body will continue to spin indefinitely in the absence of any external forces. A good example of this is the Earth spinning on its axis. In many respects angular quantities are no different than the corresponding linear quantities. Just as a linearly moving body has an amount of kinetic energy in it due to its velocity and mass, a spinning body also has kinetic energy due to its angular velocity and its mass (in the angular case the shape and distribution of mass matters as well). Since energy is always conserved, the spinning object must be subject to some outside manipulation if it is to change its speed.

Answer 4

newton's laws are all extendable to rotational motion

newton's first law states that an object in motion stays in motion in the absence of outside forces

extended to rotations, we can say that an object in rotation stays in constant rotation unless acted on by an outside TORQUE

just as forces cause changes in motion, torques cause change in rotational motions...so yes, you are correct...however, on Earth there are almost always forces (like friction) that will slow motion or rotation, but in the absence of torques, rotation will stay constant