An object executes circular motion with a constant speed whenever the net force on it acts perpendicular to its velocity. What happens to the speed if the force is not perpendicular?
If the net force acting on an object is not perpendicular to its velocity, the object will no longer continue moving in a perfect circle with a constant speed. Instead, the object will accelerate in the direction of the net force, which will cause a change in its speed.
To understand why this happens, we can use the concept of centripetal force. When an object moves in a circular path at a constant speed, there must be a force acting towards the center of the circle, known as the centripetal force. This force is responsible for keeping the object in the circular motion.
In the case where the net force is not perpendicular to the velocity, there will be two components of the net force: one perpendicular to the velocity and responsible for providing the centripetal force, and another parallel to the velocity.
The component of the force parallel to the velocity will cause the object to accelerate in that direction, either increasing or decreasing its speed depending on the direction of the force. As a result, the object will no longer move in a perfect circle with a constant speed.
If the force is in the same direction as the velocity, the object will experience an increase in speed. On the other hand, if the force is in the opposite direction as the velocity, the object will experience a decrease in speed.