Question

Can a single force applied to a body change both its translational and rotational motion? Explain and provide two different examples.

Answer 1

Yes.

applying a force directly through the center of mass of an object. You will only change the translational motion. There will be no rotational motion change. Now, consider applying a force that is only tangential to the object. It’s easier if you think in terms of a disc or a sphere. The force has no component through the center of mass, but it is applied to a radius at a right angle. This will change only the rotational motion and not the translational.

Finally, think about applying a force that has a component through the center of mass and another component at right angle to the radius. This will cause both a translational motion change and a rotational motion change.

Suppose there is a thin rod AB of some length 'l' present in isolated space, away from any other body. Now, you somehow manage to exert a force 'F' on one of it's end (say B).

• Now for transnational motion, it will accelerate with an acceleration F/m where m is it's mass.
• But it will have a rotational motion as well. It will be because of the torque produced by the same force.
• Thus it will have a combination of transnational and rotational motion.

You can always say, that a force on an extended body will have two effects. Rotational and transnational.