Centripetal force is the net force directed toward the center of a circular path that keeps an object moving in that circle. It is not a new kind of force; it's a role played by real forces like the magnetic force on a moving charge or the Coulomb attraction between an electron and a nucleus.
Centripetal force is whatever net force points toward the center of an object's circular path, with magnitude F = mv²/r. The crucial idea is that 'centripetal' describes a job, not a type of force. Gravity, tension, friction, the Coulomb force, or the magnetic force can all play the centripetal role. Nothing labeled 'centripetal force' ever goes on a free-body diagram by itself.
In AP Physics 2, the term connects to Topic 7.1 (Systems and Fundamental Forces) because the fundamental forces you study, especially the electromagnetic force, are what actually supply the inward pull. A charged particle moving perpendicular to a magnetic field curves into a circle because the magnetic force qvB acts as the centripetal force, giving you qvB = mv²/r. An electron in a classical atom model orbits because the Coulomb attraction to the nucleus supplies mv²/r. Same equation from Physics 1, new forces filling the role.
This term lives in Topic 7.1, Systems and Fundamental Forces, where the course zooms out to the four fundamental forces and how they govern systems from atoms to planets. Centripetal force is the bridge between that big-picture idea and actual problem solving. When the exam asks you to find the radius of a charged particle's path in a magnetic field, or to reason about why an electron stays bound to a nucleus, you're setting a fundamental force equal to mv²/r. It's one of the most reliable equation-pairing moves in the course, and it also feeds energy-level reasoning, since the classical orbiting-electron picture is the starting point that quantized energy levels later replace.
Keep studying AP Physics 2 Unit 7
Coulomb's Law (Unit 7)
In a classical model of the atom, the Coulomb attraction between the electron and the nucleus is the centripetal force. Setting kq₁q₂/r² equal to mv²/r lets you solve for orbital speed or radius, the exact setup that leads into discussions of energy levels.
Centrifugal Force (Unit 7)
Centrifugal force is the outward 'force' you feel in a rotating frame, like being pushed against a car door in a turn. In the inertial frames AP uses, it isn't a real force at all. Your body is just trying to go straight while the car curves under you.
Tangential Velocity (Unit 7)
Centripetal force changes the direction of velocity, never its magnitude, because it always points perpendicular to the motion. That's why a magnetic force can bend a charge into a circle without doing any work on it, so the particle's speed and kinetic energy stay constant.
Radius of Curvature (Unit 7)
Solving F = mv²/r for r tells you how tightly a path curves. For a charge in a magnetic field, r = mv/(qB), which is how mass spectrometers separate particles by mass-to-charge ratio. Bigger mass or speed means a wider circle; stronger field or charge means a tighter one.
No released FRQ in AP Physics 2 has needed the phrase 'centripetal force' as an answer by itself, but the concept powers a classic question type, which is a charged particle moving in a circle inside a magnetic or electric field. Multiple-choice stems ask which force provides the centripetal force, what happens to the radius if speed or field strength changes, or why the magnetic force does no work on the circling charge. On FRQs, the expected move is to identify the real force (qvB or kq₁q₂/r²), set it equal to mv²/r, and solve or reason proportionally. The fastest way to lose credit is drawing 'centripetal force' as its own arrow on a free-body diagram instead of labeling the actual force that supplies it.
Centripetal force points toward the center and is real (it's gravity, tension, or an electromagnetic force doing the job). Centrifugal force points away from the center and is fictitious; it only appears when you analyze motion from inside a rotating frame. On the AP exam you work in inertial frames, so the answer to 'what force pushes the object outward?' is almost always 'nothing, the object's inertia carries it tangentially while a real inward force bends its path.'
Centripetal force is a role, not a type of force; a real force like the magnetic force, Coulomb force, gravity, or tension must supply the inward mv²/r.
Never put a separate 'centripetal force' arrow on a free-body diagram; label the actual force that points toward the center.
For a charge moving perpendicular to a magnetic field, qvB = mv²/r gives the radius r = mv/(qB), the equation behind mass spectrometer problems.
In the classical atom model, the Coulomb attraction between electron and nucleus acts as the centripetal force, which sets up the physics behind energy levels.
Because centripetal force is always perpendicular to velocity, it does no work, so a particle circling in a magnetic field keeps a constant speed and kinetic energy.
Centrifugal force is fictitious in the inertial frames AP Physics uses; the outward 'push' you feel is just inertia.
It's the net inward force, with magnitude mv²/r, that keeps an object moving in a circle. In AP Physics 2 it's usually supplied by an electromagnetic force, like qvB on a charge in a magnetic field or the Coulomb attraction in an atom.
Yes and no. The inward pull is completely real, but 'centripetal' just names the direction and role. Some actual force (magnetic, electric, gravitational, tension) must be doing the pulling, so you never label a diagram arrow 'centripetal force' by itself.
Centripetal force is the real inward force that bends an object's path into a circle. Centrifugal force is the apparent outward force you feel in a rotating frame, and it's fictitious in the inertial frames AP problems use. Saying 'centrifugal force pushes the object out' on an FRQ explanation will cost you.
The magnetic force on a moving charge is always perpendicular to its velocity, so it constantly turns the particle without speeding it up or slowing it down. That perpendicular force acts as the centripetal force, giving qvB = mv²/r and a circular path of radius r = mv/(qB).
No. Centripetal force is always perpendicular to the object's velocity, so it does zero work. That's why a charge circling in a uniform magnetic field keeps constant speed and constant kinetic energy.