Does atmospheric entry shake the craft or does the process force the craft to fly in a straight line without causing vibrations?
Sci-fi movies and all have the craft shake very slightly. It would seem it would shake but why then?
It really depends on a few possible variables. Firstly, the atmosphere isn't 100% the same density over a certain area which in combination with atmospheric movement can cause vibrations especially once the atmosphere begins to thickens (same as plane turbulence). Secondly, the design of the re-entry craft will change its characteristics; a plate will experience more vibrations and wobbles than say a spear because of the difference in how the air flows around it. Thirdly, when entering the atmosphere large amounts of energy cause the craft to slow down. This gets input as just compression of air and some friction against the craft and released as a mix of heat, sound and some kinetic energy. This kinetic energy will also vary based on the craft but it could cause anything from slight vibrations to larger wobbles.
This onboard video from the 2014 Orion spacecraft reentry test shows what looks like a pretty smooth ride. During the peak heating period there's a dramatic plasma tail visible, but starting around 1:45 in the video you can see the motion of the horizon, indicating that the capsule is rocking smoothly rather than shuddering at all. Early, smaller capsules like Gemini and Mercury may have had a slightly rougher ride, but I would guess nowhere near what movies like The Right Stuff or Apollo 13 suggest.