Site investigation and subsurface exploration that are vital for characterizing soil properties often face challenges in providing large reaction forces necessary to penetrate through stiff or deep layers. To provide sufficient reaction forces, the rigs typically have large sizes that can make mobility and accessibility challenging and increase the carbon footprint. This paper investigates a plant root-inspired strategy called circumnutation-inspired motion (CIM) for soil penetration which mobilizes lower vertical penetration forces (Fz) and compares it with the forces generated during quasi-static penetration (i.e., CPT). This experimental investigation uses a robotic arm to penetrate CIM probes in uniform specimens of clay and sand. The CIM probe has a conical tip and is bent at an angle. During penetration, the probe is rotated at a constant angular velocity while it is advanced at a constant vertical velocity. The measured Fz for both soil types decays exponentially by factors as high as 10 with increasing relative velocity, defined as the ratio of the tangential to the vertical velocity of the probe tip. Torques for both soils increase with initial increases in relative velocity which plateau at greater relative velocity values. The cumulative total work (WT) has similar magnitude with initial increase in relative velocity, indicating that the Fz can be significantly reduced while the energy used remains relatively constant. The range of relative velocity up to which WT does not significantly increase (< 25% increase) is higher for sands than clays; however, in both soils this produces a reduction in Fz of about 50%. Using CIM can produce a significant reduction in Fz compared to quasi-static penetration while limiting the increase in total energy required to penetrate soil. The CIM penetration strategy could be implemented to perform site investigation activities, such as obtaining samples or installing sensors, using smaller-sized rigs.