Physics · Laws Of Motion · NEET
No. Centripetal force is not a new force like gravity or friction. It is just the NAME we give to the net inward force, whatever is actually causing it. For a stone tied to a string it is the tension; for a car on a flat road it is friction; for a planet around the Sun it is gravity. So when a question asks for the centripetal force, you must find which real force is pointing toward the centre and set it equal to mv²/r.
Centripetal force is real and points toward the centre — it is the actual pull that bends the path into a circle. Centrifugal force is not a real force; it is a pseudo (imaginary) force that you only feel when you sit inside the rotating frame, and it points outward. In NEET, always solve from the ground (inertial) frame and use only centripetal force = mv²/r. Do not add a centrifugal force in the ground frame.
You must identify the real inward force each time. String tied to a mass: tension T. Car on a level circular road: friction f. Car on a banked road at the ideal speed: the horizontal component of the normal reaction. Planet or satellite: gravitational force. Electron in an atom (Bohr model): electrostatic attraction. The idea is always the same — one real force (or a component) supplies mv²/r toward the centre.
No, in uniform circular motion centripetal force does zero work. The force points toward the centre while the displacement is along the circle (tangential), so the angle between force and displacement is 90°. Since W = F·s·cos90° = 0, the force does no work and the speed stays constant. This is why the body keeps the same speed even though a force acts on it — the force only changes the DIRECTION of velocity, not its magnitude.
In uniform circular motion the speed is constant, so there is no force needed along the direction of motion. But the velocity direction keeps changing, and the change in velocity always points inward, toward the centre. By Newton's second law, force is in the direction of the change in velocity (acceleration), so the net force must point toward the centre. This inward acceleration is the centripetal acceleration a = v²/r.
One end of a string of length l is connected to a particle of mass m and the other end to a small peg on a smooth horizontal table. If the particle moves in a circle with speed v, the net force on the particle (directed towards the centre) is (T = tension in the string):
A bob is whirled in a horizontal circle by a string at an initial angular speed ω, and the tension in the string is T. If the angular speed becomes 2ω at the same radius, the tension becomes:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
F = mv²/r, where m is mass, v is the speed, and r is the radius of the circle. Using angular speed ω (since v = rω), it can also be written as F = mrω². Both forms give the same inward force.
It always acts toward the centre of the circular path, along the radius. It is perpendicular to the velocity, which points along the tangent to the circle.
No. Centrifugal force is a pseudo force that appears only in a rotating (non-inertial) frame. In the ground frame used for NEET problems, only the real inward centripetal force exists.
Because the centripetal force is perpendicular to the velocity, it does no work (W = F s cos90° = 0). It changes only the direction of velocity, so in uniform circular motion the speed stays constant.
Centripetal acceleration a = v²/r is the inward acceleration of the body. Centripetal force F = ma = mv²/r is the net inward force that produces that acceleration. Force = mass × acceleration links them.
