https://brtkwr.com/tags/physics/Recent content in Physics on brtkwr.comHugoenSun, 03 May 2026 08:00:00 +0000https://brtkwr.com/posts/2026-05-03-optimal-cycling-speed-in-the-rain/Sun, 03 May 2026 08:00:00 +0000https://brtkwr.com/posts/2026-05-03-optimal-cycling-speed-in-the-rain/<p><strong>TL;DR:</strong> I thought there was. There isn&rsquo;t, unless there&rsquo;s a tailwind. In vertical rain, faster is always drier.</p> <h2 id="motivation"> Motivation <a class="heading-link" href="#motivation"> <i class="fa-solid fa-link" aria-hidden="true" title="Link to heading"></i> <span class="sr-only">Link to heading</span> </a> </h2> <p>I was cycling home yesterday in heavy rain and started wondering about the right speed. Slower means more time getting drizzled on. Faster means more rain per second on my front. It felt like there had to be a sweet spot.</p> <h2 id="the-setup"> The setup <a class="heading-link" href="#the-setup"> <i class="fa-solid fa-link" aria-hidden="true" title="Link to heading"></i> <span class="sr-only">Link to heading</span> </a> </h2> <p>Picture rain falling at speed $v_r$, with $\rho$ drops per cubic metre. I cycle at speed $v$ over distance $D$. Let $A_t$ be the area of my head and shoulders (top), and $A_f$ the area of my chest (front).</p>https://brtkwr.com/posts/2015-03-10-how-well-does-population-distribution/Tue, 10 Mar 2015 12:50:00 +0000https://brtkwr.com/posts/2015-03-10-how-well-does-population-distribution/<p>Previously, we tried to predict 90th percentile evacuation time $T{90}$ determined from ABM simulation using 90th percentile free flow clearance time $T90f$. Bigger the city, greater we can expect $T90f$ to be since it would take longer to traverse. Plotting $T90f$ vs $T90$ produces the figure below. $T90f$ under predicts $T90$ with a poor fit ($R=0.31$) but it is clear that $T90$ is never less than $T90f$!</p> <p><img src="../../images/pop-dist/T90f-T90.png" alt="T90f vs T90"></p>