In a study published this month by the scientific journal Nature, Erica Chenoweth and Margherita Belgioioso look at what they call “the physics of dissent” drawing on the simple law that momentum equals mass times velocity (p=mv).

“When movements maintain mass and velocity, they maintain momentum,” the authors tell us, and momentum is what’s required to achieve results…

In Russia, where activists opposed to President Vladimir Putin are routinely jailed and often murdered, cops beat protesters with grim savagery. Now they are threatening to separate arrested protesters from their children, and to jail opposition leaders for years on specious charges of corruption. Yet the protests keep growing, and Putin’s grip on power begins to be the subject of speculation.

And in Hong Kong, the public rebellion against Beijing with mass protests week after week poses a growing threat to the authority there of Chinese President Xi Jinping, whose representative has been humiliated and forced to withdraw a controversial extradition law. To push back against the tyranny of the Chinese Communist Party, as many as two million people—a quarter of Hong Kong’s population—went onto the streets in a single march.