Can Drops Travel in Air?
Figure Out How Many Water Drops Can Reach a Wall That Is Six Feet Away
- Length: 60 Minutes
Students will investigate the number of water droplets that make “contact” with a wall from different distances when propelled in a manner that simulates a sneeze or cough.
The virus that causes coronavirus disease travels mostly in water droplets that we expel when we sneeze, cough, talk and sing. Experts advise that we keep a “social distance” of at least six feet away from others to minimize the possibility of droplets being passed between us and those nearby. This physical distance, along with wearing masks and frequent handwashing, help us to slow and stop the spread of coronavirus and similar microbes.
According to the Centers for Disease Control and Prevention (CDC), respiratory droplets of various sizes are the principal mode by which people are infected with SARS-CoV-2 (the coronavirus that causes COVID-19). Large droplets, which may even be visible, fall out of the air rapidly, within seconds to minutes. Smaller droplets and particles, referred to as aerosols, can remain suspended in air for hours and travel with air currents. The epidemiology of SARS-CoV-2 suggests that most infections are spread through “close contact” (being with six feet of an individual with the infection for more than 15 minutes).
Microbes can be transmitted in water droplets, because water molecules are attracted very strongly to one another, and they also hold onto many other substances. Water molecules act like tiny magnets with each other. Every liquid water molecule has a positive end and a negative end. The forces of attraction between these opposite charges bring the molecules together very tightly. Attraction among molecules of the same kind is called cohesion. The forces of attraction among the molecules in most liquids are not as strong as those observed in water molecules. The “stickiness” of water accounts for much of its behavior, including the formation of rounded droplets, and the ability to creep upward inside a narrow tube (capillary action).
- Objectives and Standards
- Materials and
- Procedure and
- Handouts and
Remember that this activity “models” how water droplets travel. In real life, Coronavirus (SARS-CoV-2) spreads mainly through person-to-person contact—especially through very fine droplets and particles released into the air when a person with the infection coughs, sneezes, sings or talks. These droplets can land in the mouths or noses of other people nearby and possibly be inhaled into the lungs. The virus also is believed to spread through contact with contaminated surfaces or tiny droplets or particles that linger in the air as aerosols. The greatest risk of spreading the virus occurs when people are close together (within about six feet). A person with SARS-CoV-2 infection can develop the illness known as COVID-19.
Objectives and Standards
Students will describe the distance traveled by water droplets and explain how their findings demonstrate the importance of physical distancing to prevent transmission of infectious diseases by respiratory droplets, such as with COVID-19.
NGSS Science & Engineering Practices
Asking questions and defining problems
Developing and using models
Planning and carrying our investigations
Materials and Setup
Can Drop Travel in Air slide deck to project during
Each student will need the following items.
- Small mirror
- Water (small amount to create water droplets and additional water to explore how far droplets travel)
- Large plastic cup or container (large enough for students to submerge an entire hand)
- Wall or wooden fence outdoors
- Ruler, yardstick or measuring tape
- 3 sheets of blank paper (81/2 x 11 inch)
- Science notebook or additional paper for recording observations
Procedure and Extensions
Ask students, Have you ever been near someone when they sneezed? What happened? [Responses may vary, but someone may say that they felt the force of the sneeze or even got wet! Accept all answers.]
Explain that they may have felt droplets of saliva and mucus that were projected into the air when the person sneezed. Yuk! Point out that saliva and mucus from the mouth and nose mostly consist of water.
Follow by asking, Have you ever looked closely at a water drop? Direct students to use the spoon to place a small amount of water onto the surface of the mirror, creating one or more droplets.
Tell students to observe the drop(s) carefully, draw one drop in their science notebooks, and write three words describing the appearance of the drop.
5. Refer to the student activity description and sheet, Investigating Droplets. You may have students do Part 1 together with you (the teacher) if they are participating with you outdoors or online at home. They will need to have a mirror handy. (Note: During the COVID-19 pandemic, it is not advisable that students remove their masks in the classroom to breathe on a mirror.)
6. If possible, have each student breathe onto the mirror. Ask, What do you see on the surface of the mirror? If not mentioned by students, point out that the fog on the mirror consists of tiny water droplets, smaller but similar to the ones they observed. Follow by asking, How far do you think these water drops might be able to travel in the air?
7. Part 2 must be conducted outside, either at school with your supervision or at home, with students working with an older child or adult. Students will write their observations to share in class.
8. Read the instructions together.
9. Have students share their recorded observations of numbers of drops at each distance: 1 foot, 3 feet and 6 feet. If possible, create a class graph that includes each student’s counts. Have students calculate the average number of drops counted for each distance.
10.Ask, What does this information tell us about how far water droplets, which are large enough to see, can travel in the air? Students should be able to conclude that fewer drops of this size are able to travel as far as six feet.
11.Follow by asking, How can we use this information to help us keep one another healthy? Use the accompanying slides to guide a discussion with the class.
Cough and sneeze into a disposable tissue or your elbow (demonstrate). Then wash your hands!
When around others during the COVID-19 pandemic, wear a mask that covers your nose and mouth.
Stay at least six feet away from people who are not part of your household, and avoid large gatherings.
12.If not mentioned by students, conclude by pointing out that scientists know droplets can enter another person through their mouth, nose and eyes. Droplets also can be breathed in or land on something that someone else touches afterward. This is how many microbes that cause illness and disease can be spread. During the COVID-19 pandemic, we must be extra careful not to spread the virus or catch it from someone else.
Evaluate and Extend
14. Watch one of the following videos with your students. Have each student write three ways they are going to protect themselves and keep others around them healthy.
Cover Coughs and Sneezes (younger students)
Centers for Disease Control and Prevention
COVID-19 Stop the Spread of Germs (older students)
Centers for Disease Control and Prevention
How Much Water Do Humans Need?Presentation
Find helpful techniques for how to teach the lesson, "How Much Water Do Humans Need?" in which students learn how much water is used and lost during a variety of common daily activities.
What Makes Water Special?Lesson
Students explore and compare the physical properties of water and oil.
Activity adapted from Covid-19! How can I Protect Myself and Others? developed by the Smithsonian Science Education Center, 2020 (https://ssec.si.edu/covid-19)
Centers for Disease Control and Prevention. 2020. Scientific Brief. SARS-CoV-2 and Potential Airborne Transmission. Oct. 5, 2020.
The COVID HACKS curriculum project is made possible thanks to the support from Laura & John Arnold and Baylor College of Medicine. Scientists, educators and physicians from Baylor College of Medicine provided content, feedback and technical reviews.