Rolling without slipping

A wheel that rolls cleanly is doing two motions at once, locked to each other. EK 6.5.B.1 gives the constraint: while rolling without slipping, the translational motion of the system's center of mass is tied to its rotation by

and over an interval by $\Delta x_{\text{cm}} = r\,\Delta\theta$, which is the form printed on the AP Physics 1 equation sheet. One full turn advances the object by exactly one circumference.

The contact point is instantaneously at rest. Its forward velocity from the translation and its backward velocity from the rotation cancel, so nothing slides and the friction acting there is static, not kinetic.

That friction dissipates no energy. EK 6.5.B.2 states that for ideal cases, rolling without slipping implies the frictional force does not dissipate any energy from the rolling system, so energy conservation applies to a ball rolling down a ramp even though friction is what makes the rolling happen. Contrast EK 6.5.C.2: once the system slips, the kinetic friction force moves relative to the surface and does dissipate energy.

Both kinetic energy terms are present. EK 6.5.A.1: $K_{\text{tot}} = K_{\text{trans}} + K_{\text{rot}}$, so a ramp problem needs rotational kinetic energy as well as the translational term.

Two boundaries: rolling friction is beyond AP Physics 1, and the quantitative link between linear and angular quantities while rolling and slipping is out of scope for Physics 1 and 2, though a qualitative explanation is expected.