If all of humanity (and perhaps the animal kingdom too for good measure) were to run East at the same time for a prolonged period of time, would the equal and opposite force of their feet pushing the ground west behind them slow down the Earth's rotation?
As it's 4.20 am where I am, and I am pretty dreadful at simple arithmetic, I welcome anybody to refine this calculation, a wiki, if you will.
Any frills to the topic, such how long they would need to walk to make a significant difference, are welcome. But any pedestrian material or remarks will be ruthlessly eliminated. Except that previous line.
Ok, The angular momentum of the spinning earth is:
$I = [2/5]mr^2$ and $ω$ = $2π/T =[ 2π/86400]$ rad/s
$mass = 5.978×10^{24}kg$,
$radius = 6.378×10^6m$
$L = [2/5]×5.978×10^{24}×6.378×10^6×6.378×10^6×[ 2π/86400]$
$L = 7.074 ×10^{33} kg.m^2s^{-1}$.
My (simple, naive) idea is to calculate the force exerted by these walking people, and I make the following sweeping assumptions.
The number of people on Earth is 7.5 billion ( give or take the odd million) and I assume they average 40 kg each. This produces a total mass of $3 × 10 ^{11}$ kg
I then assume that every second, they take one step forward, on a synchronised system, so resulting in a push backwards against the Earth and treating this as an acceleration, this produces a force of $3 ×10^{11} kg.m/s^2$
So you have a force of $3×10^{11} kg.m/s^2$ trying to reduce an angular momentum of $ 7.074 ×10^{33} kg.m^2s^{-1}$.
It may take a while to notice any change.
Since answering this question, I have VTC as there is a duplicate here: Can humans slow down the Earth?
