ConceptMechanics
← All conceptsCircular motion & gravitation
uniform circular motion (v, ω, T, f), centripetal acceleration v2/r=ω2·r and force, universal gravitation F=GMm/r2, gravity provides centripetal force, orbital/first-cosmic velocity, satellite period-radius (Kepler), surface g=GM/R2
17 ways this goes wrong. Each one is a named misconception the questions are built to catch.
- Centripetal force is an extra forceAdds centripetal force as a separate force on the free-body diagram instead of identifying it as the net of real forces.→
- Centripetal force points outwardDirects the centripetal (net) force outward, away from the center, instead of toward it.→
- Escape velocity depends on object massBelieves the escape (cosmic) velocity from a planet depends on the escaping object's mass.→
- Field strength uses orbiting massIncludes the satellite's mass in g=GM/r2, where only the central body's mass M appears.→
- Gravity as 1/r not 1/r2Uses an inverse-distance (1/r) dependence for gravitational force or field instead of inverse-square (1/r2).→
- Higher orbit means fasterBelieves a satellite in a higher orbit moves faster, contradicting v=√GM/r.→
- Kepler period-radius relation wrongUses a linear T proportional to r relation instead of T2 proportional to r3.→
- Min speed at top ignores gravityFinds the minimum speed at the top of a vertical loop without letting gravity supply the centripetal force.→
- Momentum unchanged in circular motionClaims momentum is constant in uniform circular motion because speed is constant, ignoring its changing direction.→
- No acceleration at constant speedConcludes acceleration is zero in uniform circular motion because the speed is constant, ignoring the direction change.→
- No gravity in orbitAsserts there is no gravity on an orbiting satellite/astronaut, rather than gravity providing the centripetal force.→
- Orbit radius used for surface gSubstitutes the orbital radius into surface g=GM/R2 instead of the planet's radius R.→
- Period/frequency invertedUses T=f instead of T=1/f, or otherwise inverts the period-frequency relationship.→
- Satellite mass kept in vKeeps the satellite's mass in the orbital-speed result, missing that v=√GM/r is independent of it.→
- Tension max at top of vertical circleAssumes string tension is greatest at the top of a vertical circle rather than at the bottom.→
- v and ω relation wrongConfuses v=ω·r, using ω/r or ω·r2, or otherwise mixes angular and linear quantities.→
- v2/r vs ω2 r confusedMismatches the centripetal acceleration formula, e.g. uses v2/r with ω, dropping or adding an r.→
