1. The problem statement, all variables and given/known data This is not a set question but a problem statement for an investigation. I am trying to understand the physics behind drinking through a straw, but not when the straw is fully submerged in the drink but at the end of the drink when the liquid and air both pass up the straw and you get the slurping noise. I understand that when the straw is fully submerged that the reduction in air pressure caused by 'sucking' means that atmospheric pressure pushes down on the liquid in the glass which then pushes it up the straw. But what mechanism causes the liquid to be sucked up when air is also present and what physics can I use to determine the differences caused by different straw diameters, air flow and pressure? I am doing a HNC mechanical engineering in the UK and currently studying the fluid mechanics module. I am about to measure air flows but just wanted a sanity check that I am on the right lines. Thanks in advance! 2. Relevant equations Bernoulli’s equation Poiseuille equation Navier-stokes equations 3. The attempt at a solution So far I think the liquid is en-trained into the air flow and up the straw due to the shear forces on the liquid because of the air flow. However the liquid is not easily transported up the straw like when it is fully submerged, due to gravity on the liquid in the absence of a sealed vacuum, adhesion of the liquid to the surface of the straw and the cohesion of the liquid causing a greater mass and greater surface area in contact with the straw wall causing a greater force required to draw it up. Also the surface tension of the liquid means the air flow struggles to en-train the liquid as the air molecules don’t want to ‘stick’ to the water molecules. If a larger diameter straw is used then there is more surface area for the liquid to adhere to and more open space for the air to bypass the liquid and travel up the middle of the straw. I have written this in a descriptive way as I am currently trying to visualise the problem and work out exactly what needs to be solved. Air velocity is key is think, the higher the velocity the more successful one will be in causing the liquid to travel the length of the straw.