Learn the science
Speed is not the whole velocity
Velocity is a vector with magnitude and direction. A bicycle rounding a curve at a steady 4 m/s keeps its speed constant but continually changes the direction of its velocity. Acceleration is change in velocity per unit time, not merely change in speed. A circular path therefore requires a net acceleration toward the center even when the speedometer reading stays steady.
Name the inward direction
For uniform circular motion, centripetal acceleration has magnitude a_c=v²/r, where v is tangential speed in m/s and r is circle radius in meters. Its direction points toward the center at each instant. The net radial force is F_net,radial=m v²/r. Centripetal describes the direction of the RESULTANT force; it is not an extra force you add alongside real interactions such as friction, tension or gravity.
What the moving arrow represents
Velocity is tangent to the circular path at each position while acceleration points toward the center. The velocity arrow changes its direction continuously. If all radial forces suddenly disappeared, the body would continue approximately along the instantaneous tangent under Newton's first law, rather than flying outward under an invented force.
Check the model’s boundaries
The digital investigation assumes an ideal particle traveling at constant speed around a circle. It does not model the mechanism maintaining that path. Real vehicles can turn using tire-road contact friction; a tethered object can turn under tension; planets orbit under gravity. Actual situations can also have a tangential acceleration if speed changes.