Physics · Laws Of Motion · NEET
Speed is constant, but velocity is NOT, because direction keeps changing. Acceleration means change in velocity (a vector), not just change in speed. In a circle the velocity vector turns, so there is a real acceleration of size v^2/r directed toward the centre. By Newton's second law F = ma, this needs a real net force of size mv^2/r. So constant speed does not mean zero force.
No. In the ground (inertial) frame there is NO outward force on the body. The only real force is the centripetal force pointing inward. The outward 'centrifugal force' you feel is a pseudo force that appears only when you sit in the rotating frame. For NEET dynamics problems solved from the ground, always write the net inward force = mv^2/r and do not add any outward force.
Centripetal force is not a new kind of force; it is the NAME of the net inward force. In real cases it is supplied by something physical: tension in a string (stone whirled in a circle), friction (car on a flat road), normal reaction (wall of a drum), gravity (satellite), or a component of them. Your job in a problem is to identify which real force points to the centre and set it equal to mv^2/r.
Straight toward the centre, along the radius, at every instant. It is always perpendicular to the velocity (which is along the tangent). Because it is perpendicular to velocity, this force does NO work, so it changes direction but not speed. That is why speed stays constant in uniform circular motion.
Write the centripetal force as F = mω²r. Here tension T supplies it, so T = mω²r. Tension is proportional to ω². If ω becomes 2ω, then T becomes (2)² = 4 times the original. This is the NEET 2024 bob question: doubling ω makes tension 4T, not 2T. Always use the ω² form to avoid this trap.
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:
A football player moving southward suddenly turns eastward with the same speed to avoid an opponent. The force that acts on the player while turning is directed:
What is the minimum velocity with which a body of mass m must enter a vertical loop of radius R so that it can complete the loop?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is applying Newton's second law to a body moving in a circle at constant speed. The net force needed is the centripetal force F = mv^2/r = mω²r, directed toward the centre. It supplies the centripetal acceleration a = v^2/r.
No. It is only the NAME of the net inward force. A real force such as tension, friction, gravity or normal reaction acts as the centripetal force in each problem.
Because velocity is a vector. Its direction keeps changing along the circle, so the velocity changes even though its size (speed) does not. That change gives an acceleration v^2/r toward the centre.
No. It is always perpendicular to the velocity, so work done = force × displacement along the force = 0. That is why the speed and kinetic energy stay constant in uniform circular motion.
Both give the same centripetal force. Use F = mv^2/r when the linear speed v is known, and F = mω²r when the angular speed ω is known. They are linked by v = ωr, so mv^2/r = mω²r.
