Rotating ship afterimages from two perspectives.
<p>In the free-float-frame perspective at left, our bouncing ball travels at constant speed in straight lines between collisions.
</p><p>In the ship-frame perspective at right, our bouncing ball experiences a radially-outward "geometric" force that acts on every ounce of its being.  
</p>
Like gravity, this force is undetectable by cell-phone accelerometers, but nonetheless potentially dangerous.
<a href="//commons.wikimedia.org/wiki/User:Unitsphere" title="User:Unitsphere">P. Fraundorf</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>