Experiments visualising the airflow when breathing, speaking and laughing, show that wearing a mask indoors can drastically reduce the risk of transmission of airborne particles. Without a mask, breath is ejected from the lungs to form a secondary plume in front of the host, increasing the risk of exposure for others. When wearing a mask, the secondary plume is no longer formed and the airborne particles instead move upwards to the upper layer of the room where they can be safely removed by a ventilation system. Read the open access publication here: https://doi.org/10.1017/jfm.2020.720 Produced by Dr Tom Crawford, an Early-Career Teaching and Outreach Fellow in Mathematics at St Edmund Hall at the University of Oxford: https://www.seh.ox.ac.uk/people/tom-crawford For more maths related content check out Tom's website https://tomrocksmaths.com/ Follow Tom: Website: https://tomrocksmaths.com/ YouTube: null Twitter: https://twitter.com/tomrocksmaths Facebook: https://www.facebook.com/tomrocksmaths/ Instagram: https://www.instagram.com/tomrocksmaths/ Get your Tom Rocks Maths merchandise here: https://beautifulequations.net/collections/tom-rocks-maths Reference: Bhagat, R., Davies Wykes, M., Dalziel, S., & Linden, P. (2020). Effects of ventilation on the indoor spread of COVID-19. Journal of Fluid Mechanics, 903, F1. doi:10.1017/jfm.2020.720 Although the relative importance of airborne transmission of the SARS-CoV-2 virus is controversial, increasing evidence suggests that understanding airflows is important for estimation of the risk of contracting COVID-19. The data available so far indicate that indoor transmission of the virus far outstrips outdoor transmission, possibly due to longer exposure times and the decreased turbulence levels (and therefore dispersion) found indoors. In this paper we discuss the role of building ventilation on the possible pathways of airborne particles and examine the fluid mechanics of the processes involved. With thanks to: Prof. Paul Linden Prof. Stuart Dalziel Dr Megan Davies Wykes Dr Rajesh Bhagat Journal of Fluid Mechanics Credits: Journal of Fluid Mechanics Martin Marek The Stuff Zone