We've all experienced it. You're walking in the hallway, the not-so-trafically-ideal hallway (we really need to invest in a double yellow line down the middle so everyone walks the right way...), and suddenly you and a stranger come face to face. You awkwardly try to maneuver around eachother, both stepping the same way...twice. I find myself in these situations daily, so I thought it'd be cool to think about the physics behind it.
As you walk forward, you have a forward momentum of mv; m being your mass, v being the velocity at which you're walking. When you and another person are walking towards eachother, you must apply a force down and at an angle that pushes you backwards, so as to stop your forward velocity and thus momentum. As you apply a force down on the ground, the ground also pushes up on your feet because, according to this guy Newton, for every action there is an equal and opposite reaction.
Depending on how long you apply the force, you will have a certain impulse which will inevitably change your velocity. Your impulse will equal the average force you exert on the ground multiplied by the duration of time during which you apply the force (J = Ft).
As the two of you sidestep eachother - laughing nervously, trying to avoid eye contact - you exert different forces down at different angles to propel you left or right. Finally, after what seems like an eternity, you both agree on a side and proceed past each other. As you begin forward again, your feet apply an increasing downward force on the ground, causing you to accelerate back up to your initial velocity before this awkward encounter.
So, there you have it: the physics of uncomfortable hallway run-ins with strangers. Next time this happens to you, think of this blog post and I hope you'll feel less awkward! More likely not, though. Either way, I hope you enjoyed!
Until next time,