Virus Particles

An animated image of an HIV virion.

I am taking a course in microbiology this semester. I saw a movie about a virus epidemic and I became mindful that the amount of time that a virus particle hangs in the air is dependent of the diameter and density of the particle.After running the calculations below on the common influenza virus, I determined that a virus particle would take 149 days to settle out of room air from a height of 6 feet in a poorly ventilated room. I gathered data from the CDC to determine the density and diameter of a common influenza virion. I used a height of 6 feet because that is the height a virion would enter the air if a person were to sneeze.

Salt Water Aquarium III

Again, I was thinking back to the salt water aquarium and became mindful of one last fluid mechanic principle. I noticed that the aquarium had a hydrometer. A hydrometer is a tube that allows for the measurement of the salinity in the tank. The density of the salt water will change based on the salt content. This makes the hydrometer float freely at different depths. The depth the hydrometer floats freely is recorded and the salinity can be determined.

Salt Water Aquarium II

I was thinking back to the saltwater aquarium that I saw yesterday and I became mindful of yet another fluid mechanic principle at work. The fish in the tank possessed a capability to obtain neutral buoyancy at any depth. This is because fish have a unique organ, called a swim bladder, that acts similar to a ballast tank on a submarine. Air can be added or released from this organ. When more air is added the fish maintains the same volume but changes its density. This allows the fish to rise in the water column without having to expend energy swimming there.

Salt Water Aquarium

I took one of my friends to the doctor today. I am always surprised about the locations that I become mindful of fluid mechanic principles. While I was sitting in the waiting room I noticed the salt water tank that was sitting in the corner of the room that was filled with unique salt water fish. I became mindful that all the fish in the tank were teardrop shaped. This is no coincidence, this is the most aerodynamic 3-D shape we have studied about, having a C_D of 0.04. This allows the fish to reduce the drag force acting on them so they are able to navigate their aquatic environment with minimal energy consumption.

Aerial Photos

I recently began hunting the Tuskegee National Forest near Auburn, AL. When I begin hunting a new area I spend a great deal of time analyzing the aerial photos of the property. While I was analyzing the aerial photos of the Tuskegee National Forest I became mindful of the fluid mechanics that allow for a quality aerial photo. Colder and less dense air in the atmosphere provide for optimal conditions for photography. This is because there are less air molecules interfering with the photo and you get a better resolution in the photograph.

Fishing Boat Drag

While I was hunting and hiking this weekend I came across a couple of fishing ponds at the Tuskegee National Forest. I began to think about when I could get my fishing gear from home and fish these ponds. I then became mindful of the drag force on a fishing boat. When me and my fishing partner get prepared for a fishing trip we always try to minimize the amount of heavy gear that we bring in the boat. I never thought about it before but this has a certain fluid mechanic reasoning. The more gear that we put in the boat, the lower it will sit in the water due to buoyancy. When traveling down the river the drag force acting on the sides of the boat are dependent on the height of water on the sides. Thus, the drag force can be minimized by removing all unneeded heavy gear from the boat.

Gunshot

Mark-45 firing on the deck of a destroyer.

Today I was mindful of the fluid behavior that takes place in a gunshot. There are several fluid principles at work here. First, there is a rapid expansion of gas due due the gunpowder that is ignited to fire the projectile. This sudden expansion carries with it a loss in energy (head loss). This flow is obviously turbulent due to the extremely high velocities coming out of the end of the barrel. The projectile produces a sonic boom caused by the supersonic speeds that the projectile is moving at.

Kármán Vortex Street

Image of a Kármán vortex street in a fluid flow.

While I was hunting today I saw a rock that was laying in a creek. I was mindful of the Kármán vortex street that was present in the flow downstream of the rock. A Kármán vortex street is a set of swirling vortices that are caused by the separation of fluid flow by a rigid object in the flow. The vortices are produced over a specific Reynold's number range which is depending on fluid properties of the fluid and the dimensions of the object obstructing the flow.