A horizontal centrifuge is more appropriately known as a “swing out” centrifuge. In every horizontal centrifuge, the tubes at rest are at an angle. It is only when the centrifuge is spinning at high speed that the tubes “swing-out” and are horizontal. It is impossible to really see this, because at high RPM you can’t even really see the tubes moving. This is why you don’t see the horizontal photo online and only see the “at rest” picture.
However, you can easily notice on the horizontal centrifuge that the tubes are not fixed to anything and can be moved when you place your hand near the rotor. This ability to move is what causes the “swing out” at high speeds. This is very different than a fixed angle centrifuge, where the tubes are fixed at an angle, cannot be moved, and will not move at high RPM.
The image below might provide some additional help in understanding the difference above. Notice arrow on the horizontal centrifuge (swinging bucket) on the right, indicating the swing out.
