We pay little attention to gravity unless we drop something on our foot or trip and fall, dismissing it as a constant vertical force acting on us. Evolving to stand and move while “zeroing out” this primary influence on our morphology is a foundational accomplishment of land-based animals. Remarkably, the design of our bodies can safely function over a lifetime within this force without much conscious vigilance. However, rather uniquely amongst animals, we can consciously attenuate our movement patterns, allowing us to continue to refine our movement kinematics. Engaging thus extends our functional/structural scope in myriad ways. This augmentation is facilitated by an accurate understanding of the qualities of the dominant force we operate within – gravity.
We know that gravity is acceleration – an increase in speed of about 30 feet per second every second. This statement is non-intuitive – how are we accelerating while it is apparent that we are not moving? A solution to this puzzle resides in established physics, validated for over 100 years but yet to percolate into common awareness1, elucidated in the short illustrated narrative below.
It is also helpful to understand how dynamic this force is, delineated in this example:
We are comfortable within and pretty much ignore the force of gravity2. However, if we apply this same force to our bodies in an unaccustomed direction it becomes quite apparent what we are dealing with, This opportunity is afforded us when we accelerate in a muscle car.
Accelerating from 0-60 miles per hour in about 2.7 seconds applies the equivalent horizontal force to our bodies as does gravity.
Before high-end BEVs, this force could only be experienced on the road in the highest-performing power cars from fabricators like Ferrari and Lamborghini.Land animals evolved to “offset” our perception of this force on our bodies, “zeroing-out” the gravitational effect, thereby often making it barely noticable3.
Recognizing that all of our surroundings and our bodies are accelerating away from the center of the earth at this rate is a foundational reframe. What we call weight is the inertia of our mass as we are forced(thrust) in a vector pointing outward from the center of Earth’s mass4. Addressing this force has been the foundational issue for life that migrated onto land from a weightless(neutral buoyancy) persistence in water.
Having loaded our primary movement mechanics onto two legs from the four we evolved with further prioritizes this issue. It is a remarkable evolutionary achievement that we stand and walk on two legs without paying much attention to this force.
It is hoped that this short illustrated guide on Special Relativity is both informative and enjoyable:
Republished with permission to use for educational purposes by the AAAS.
POSTSCRIPT
Our conscious attention can further refine our evolution/development in movement within the gravitational effect. The posts in the Stance and Gait Mechanics category on this blog, particularly those exploring using accelerating sensing hardware as gait characteristics feedback, delve into aspects of fine-tuning activities. General Relativity does not need to be understood to be applied beneficially, just the application of information on the qualities of acceleration to our movements. However, it is a fascinating attribute of our encompassing physics to explore.5
FOOTNOTES
- The story of this proof using Gravitational Lensing is covered in the movie “Einstein and Eddington“. As of early 2024, AI LLMs still need to be specifically prompted to discuss gravity in non-Newtonian terms or they will otherwise perpetuate pre-General-Relativistic physics. ↩︎
- We evolved to null out the gravitational effect. Accelerations we experience in our Vestibular System “zero out” the constant acceleration of gravity.
In the rate of change of velocity calculation, as we sense it:
y = mx + b (m is the slope of the rate of change in velocity)
b = 9.8 meters/second2, which is the gravitational offset. ↩︎ - Gravity was not formally conceptualized until 1687 by Sir Isaac Newton, extending the work of Galileo Galilei ~100 years earlier. Before this work, gravity was likely not perceived – an implicit assumption. ↩︎
- Thrust can still be understood as a force in the traditional Newtonian sense, used to overcome or work within the geodesics of spacetime—essentially, the ‘paths’ that objects follow within the curved spacetime fabric. ↩︎
- Other posts in this Blog exploring attributes and influences of the gravitational effect: GRAVITY ↩︎