What force provides the centripetal force when you swing a stopper with a string above your head horizontally?
If the string breaks suddenly, in what direction will the stopper fly to?
When you swing a stopper with a string above your head horizontally, the force that provides the centripetal force is tension in the string. The tension in the string acts towards the center of the circular motion and is responsible for keeping the stopper moving in a circular path.
Now, if the string suddenly breaks, the stopper will continue to move in a straight line tangent to its circular path at the point where the string broke. This is due to the law of inertia, which states that an object in motion will keep moving in a straight line at a constant velocity, unless acted upon by an external force.
So, when the string breaks, there is no longer a centripetal force acting on the stopper to keep it in circular motion. Thus, the stopper will fly off in the direction of the tangent line to its circular path at the point where the string broke.