1. Why Doesn't a Drink Rise Just Because You Put a Straw In?
Immediately after placing a straw in a glass, the liquid level inside the straw is the same height as the level in the glass. The drink does not rise on its own because the same atmospheric pressure acts on the liquid surface inside the straw and on the surface in the glass [2]. When you suck, only the air inside the straw decreases, lowering the pressure there. As a result, the force pushing on the liquid surface inside the straw becomes smaller than the force pushing on the surface in the glass. Because of this difference, the drink is pushed into the straw [2]. Imagine a large hand pressing down on the drink. If the hand moves away only inside the straw, the drink is pushed up into that space. In reality, it is not a hand but the surrounding air that is pushing. Explanations note that the mouth does not pull the drink; rather, the higher external pressure pushes the drink toward the mouth [1]. So, what happens to the air in the straw when you suck?
2. How Does Sucking Lower the Air Pressure Inside a Straw?
When you inhale, the diaphragm below the chest contracts and moves down, expanding the space around the chest. This lowers the pressure in the lungs below atmospheric pressure, allowing air to flow in. This is the general mechanism of breathing. When sucking through a straw, air is pulled from the straw into the lungs, lowering the pressure inside. Consequently, the atmospheric pressure acting on the liquid surface in the glass becomes greater, pushing the drink up the straw to the mouth [1]. The act of "sucking" serves only to lower the pressure. The force that actually moves the drink comes from the outside air. This raises a simple question: if you could remove all the air from your mouth, how high would the drink rise?
3. How High Can Air Pressure Push Water, Even in a Perfect Vacuum?
When using atmospheric pressure to push liquid up like in a straw, the height of the water column that air pressure can support is introduced as about 30 feet, or roughly 9 meters, at sea level [1]. Torricelli determined in the 1640s that the water column supported by atmospheric pressure is about 10.33 meters. This figure is derived from experiments using mercury [3]. Mercury is about 13.6 times heavier than water, so the height of the mercury column supported by the same atmospheric pressure is about 760 millimeters [3]. Conversely, multiplying 760 millimeters by 13.6 gives about 10.3 meters, and the calculations align [3]. According to the Japan Meteorological Agency, atmospheric pressure was first observed using Torricelli's mercury barometer in 1643 [4]. Since sources vary by one year, this article uses the 1640s. The pressure difference needed to lift a water column by 1 meter is about 9.8 kilopascals. Since 1 atmosphere is about 101 kilopascals, about 1/10 of atmospheric pressure is used for every meter. It is used up at about 10 meters. This is a value calculated from density and gravity. So, how high above the drink can we actually sip?
4. Why Is the Real Height for Drinking Much Lower Than 10 Meters?
The real limit is much lower than 10 meters. Because it is impossible to create a perfect vacuum in a human mouth, the actual limit is lower than 10 meters [2]. One explanation notes that while some people find it difficult to drink from a 3-foot (about 0.9 meter) straw, others can drink from locations about 8 feet (about 2.4 meters) above the drink [2]. This shows large individual differences. What matters is not the total length of the straw, but the height difference between the liquid surface and the mouth [2]. Even with a long straw, if the height difference from the liquid surface is small, you can drink. In space, where there is no atmospheric pressure, you cannot drink liquids through a straw [1]. There is no air to push it. However, there are reports of experiments that exceeded the 10-meter wall.
5. How Did an Experiment With Detergent Water Go Beyond the 10-Meter Limit?
A paper published in PMC reports that a siphon 15.4 meters tall was created using water with surfactant, exceeding Torricelli's limit of 10.33 meters [3]. This is about 1.5 times 10.33 meters. A siphon is a mechanism that lifts water to a high point using a tube and then flows it to a lower point. With ordinary water, as the height approaches the limit, bubbles form in the water, and the flow stops. The authors suggest that adding detergent, which makes bubbles less likely to form, may be related to exceeding the limit [3]. However, in this experiment, the flow stopped after 224 seconds, or about 3 minutes and 44 seconds [3]. Also, this was a siphon experiment, not a case of drinking a drink from 15 meters high with a straw. Straws using pressure mechanisms cannot be this long. So, how have straw shapes changed?
6. How Did Straws Change From Wheat Stalks to Paper to Bendable Designs?
About 5,000 years ago, Sumerians are thought to have used slender tubes made of precious metals to drink beer. This was to avoid sedimented grain residue [6][5]. Marvin Stone, the manager of a company that made cigarette papers in the United States, filed the first patent for a drinking straw in 1888 [5]. It is said he made it by wrapping paper around a pencil, gluing it, and coating it with wax, because rye straw straws deteriorated in drinks [5]. In Japan, it is said that Kazuichi Kawasaki began making straws using wheat stalks in Kojima, Okayama Prefecture, around 1901 (Meiji 34) [7]. The technology used for making straw hats was applied [6]. The bendable straw is said to have been devised by Joseph Friedman, who saw his daughter struggling to drink a milkshake. He threaded a screw through the straw and wound thread to create accordion-like grooves. The patent was in 1937, and commercial sales began in 1947 [5]. Straws in every era are slender tubes open at both ends. What changed were the materials and shape, driven by human problems.
7. How Can You See the Pushing Force of a Straw at Home?
You can try this at home. Put water in a glass and insert a straw. Cover the top hole of the straw with your finger and lift it gently. Watch to see if water remains in the straw. Then, release your finger. What happens? Try to explain the reason using the same thinking as when drinking. Do this in a place where spills are not a problem. To investigate further, look for "atmospheric pressure" and "Torricelli's experiment" in science books and read why the mercury column becomes about 760 millimeters. At home, you can also see how how much water remains in the straw when you lift it to different heights.