Centripetal Acceleration and Centripetal Force

Circular motion occurs when an object moves along a circular path with a constant or varying speed. For an object to follow this path, a force must act continuously toward the centre of the circle. This inward force is called centripetal force, which prevents the object from moving in a straight line due to inertia. Examples of circular motion include the revolution of planets around the Sun, the motion of a satellite around Earth, and a stone tied to a string being whirled in a circle.

• The Moon orbits the Earth in a definite path, continuously changing its direction and speed. A force must be acting on the moon to keep it in orbit, directed toward the centre of the earth. Without this force, the Moon would move in a straight line instead of orbiting the Earth.
• Similarly, planets in the solar system revolve around the Sun in a similar manner. The Sun exerts a gravitational force on the planets, pulling them toward itself. This force acts toward the centre of the Sun, keeping the planets in their orbits.
• From the experiment with a stone tied to a string, we see that an inward force (centripetal force) is necessary for circular motion. The gravitational force between celestial bodies acts as this centripetal force, ensuring their orbital motion.

1. Aim: To demonstrate the effect of centripetal force on an object moving in a circular path and observe its motion when the force is removed.

2. Requirements: a stone and strong string

3. Procedure

1. Tie one end of the string to the stone.
2. Hold the other end of the string firmly in your hand.
3. Rotate the string so that the stone moves in a circular path.
4. Observe the force applied and its direction (towards the centre).
5. Release the string suddenly and observe the motion of the stone.

A stone tied to a string, moving along a circular path and its velocity in tangential direction

4. Observation

• While the string is held, the stone moves in a circular path due to the inward force (centripetal force).
• When the string is released, the stone moves in a straight-line path (tangent to the circle at the point of release).

5. Conclusion: An object moving in a circular path experiences a force directed toward the centre, called centripetal force. When this force is removed, the object moves in a straight-line path due to inertia, proving that an external force is required to maintain circular motion.