Behind the Mask – the forces of Attraction

Age group 1st – 3rd year, TY

Total time 1.5hr

Notes for teachers and parents/carers

This activity sheet is designed to be carried out at home or school under supervision by a teacher or any adult who can help direct the work which involves some basic mathematical calculations. The instructions are directed to the adult. Most of the information needed to answer the questions is given on the main sheet, but we do encourage the students to think for themselves and to research the topic further. .

Outline: To learn about the history and science behind wearing masks to protect against contagious diseases

Junior Cycle Curriculum Links

The student should be enabled to

  • produce and select data, critically analyse data to identify patterns and relationships, identify anomalous observations and justify conclusions (Investigating in Science, The Nature of Science)
  • investigate patterns and relationships between physical observables (Systems and Interactions, Physical World)
  • Represent situations − use tables, diagrams and graphs as a tool for analysing relations with tables diagrams and graphs (Maths, Algebra)

Statements of Learning

  • Describes, illustrates, interprets, predicts and explains patterns and relationships (16)

  • Observes and evaluates empirical events and processes and draws valid deductions and conclusions (18)

  • Values the role and contribution of science and technology to society, and their personal, social and global importance (19)

Key Skills

  • Managing information and thinking
  • Communicating
  • Being literate

1. To mask or not to mask?

In the last twelve months we are all changing our habits by wearing masks in enclosed public spaces. We know we are doing this to protect ourselves and others from getting infected with COVID-19. But how do the masks protect against infections?

How have you found wearing masks in school and in public places? Have you noticed if you have got sick less or more this past year? Why do you think some people don’t want to wear masks in public places? Make a note of your thoughts. Can you remember when mask wearing was made obligatory in public places?

Many governments did not initially recommend wearing masks in the first part of the lock-down as they were following the World Health Organisation advice at the time. When the WHO reexamined scientific evidence, they advised mask wearing in June 2020. Ireland made masks compulsory in July 2020 in any indoor public space. China and other Asian countries made mask wearing compulsory very early in the pandemic, because they had previous positive experience of reducing the SARS virus in 2002 with such methods. For example, Vietnam with a population of 97 million, where mask wearing is compulsory since the pandemic began, has had only 35 deaths, and 1,500 COVID-19 cases (February 2021).

Check out Professor Luke O’Neill’s Science Podcast talking about the science of masks https://www.newstalk.com/news/luke-o-neill-mask-hypothesis-immunity-1075750

Thankfully, there are now several vaccines available that will protect us once we are vaccinated. But these will take time to be rolled out, and in the meantime, masks are one of our main protections against infection for some time.


Did you know?

  • In 1905 Alice Hamilton, a US physician, published one of the first academic papers suggesting that doctors were passing dangerous bacteria to their patients, from their nose and mouth, during surgery, and advocating for face masks. Doctors however continued to scoff at mask wearing during surgery, until the 1920s.
  • In 1910 a Chinese doctor Wu Lien Teh was sent to deal with a fierce outbreak of pneumonic plague in northeastern China. He realised it was being carried in the air and urged everyone to cover their faces. Deaths were rapidly reduced and the plague stamped out. The world sat up and noticed, and adopted the face mask. (Source)

2. What do masks do?

Ask the students the following questions to get started:

Name a few jobs where people wear protective masks, and what they are protecting themselves against/using it for? (e.g. welding shield, volatile liquids mask, doctors, carpenters, scuba mask, etc). How do you think these types of masks work? What do they stop entering or escaping and why? (In general the materials in the different masks are designed to trap different particles in question)

Let’s talk about masks and Covid-19.

Do you know how Covid-19 travels in the air? What is coming out of our mouths when we cough, sneeze or talk, that helps Covid-19 travel along? Covid-19 as well as other viruses fly out of our mouths in droplets of water moisture. Most droplets are heavy enough that they fall within two metres or so, hence the two metre social distancing rule. A mask can trap the heavy and lighter water droplets significantly. Even a basic home-made material mask can filter about 60-70% of air-borne particles. But how do they really work? Let’s experiment and see….

3. Put your mask where your mouth is

In this experiment we will test about three types of masks, depending on what you have available. Before you begin, think about what mask you think will work best and why. This is your hypothesis and we will now test it in the experiment.

Note: Surgical masks are made of three layers: a middle layer of extra fine glass fibres or synthetic microfibres covered on both sides by special acrylic fibres. Medical N95 respirators consists of multiple layers of nonwoven fabric, often made from polypropylene. Home-made or bought material masks can be made of any material with tightly woven fibres.

What you need

2-3 people (groups of 2-3 if in a classroom setting), tea-light candle, plate, 3 types of masks (e.g. 1 medical grade mask, home-made material mask with one layer, material mask with two layers),talc powder/white flour, torch, measuring tape/ruler

Procedure

  1. Place the tea-light candle on a plate one metre from the person who will try to blow it out. (Be cautious with the flame and never leave it unattended when lit)
  2. Squeeze a small amount of talc powder out of the container into the air space between the candle and the person (before they blow). Quickly shine the torch through the particles and observe how they move. (Particles in air will always have some slight movement anyway)
  3. Firstly without a mask on, ask the person to try to blow out the candle using their normal blowing strength, as if blowing out a candle on a cake.
  4. Turn on your torch again and shine it through the air mass toward the candle. Squeeze out some more powder into the air near the person blowing, and ask them to blow again. See how fast the dust particles now move. Are they moving faster or slower? Turn off your torch now.
  5. Slowly move the candle toward the person until they manage to blow it out. Write down the distance at which it is blown out. (Make sure they don’t lean forward to shorten the distance between them at the candle, so you can measure it accurately).
  6. Repeat this with the person now blowing as hard as they can without any mask on. (This can represent approximately the force of a sneeze.)
  7. Now repeat this procedure with normal and hard blowing with different masks; for example with a one-layered material mask, then a two-layered material mask, and finally a medical grade disposable mask. Feel free to vary this depending on what you have available. If you wish you can try putting powder in the air and viewing it with the torch again.
  8. Make a note of which face-mask causes most and least movement of the talc/flour particles as viewed with the torch. Write down at what distance was the candle blown out each time.
  9. You can repeat this with a number of people if you wish, but remember to use clean masks every time!
Talc powder particles help to see how the air particles move when someone blows or sneezes

Write all your distance answers in a table like the one below:

Mask type Candle blown out at
normal strength
Candle blown out at
maximum strength?
No mask

1 layered mask

2 layered mask

Medical grade mask

Watch this video and think about your results.

4. Analysis

From your table,

  • Can you tell which mask worked best?
  • Were you surprised, or did it match your hypothesis?
  • Was there a significant difference in the distance between blowing normally and then with strength?
  • What does this tell us about the mask’s ability to stop a sneeze?
  • What physical phenomena do you think act on the person’s breath once they wear a mask?
  • Are there any chemical phenomena which might act on the air current?

5. Here’s the Science

There are four different phenomenon happening at the same time.

Condensation: Water droplets condense on the inside of the mask thereby trapping a lot of the virus-laiden droplets. Friction with the mask fibres reduces the momentum of the air current thereby limiting the distance traveled by the particles that do make it through the mask.

Let’s recap!

Friction is a force that opposes motion when two objects are placed in contact. Place your hand in front of your mouth and blow. Can you feel the light friction of the air current on your skin? Where else do we find friction? Rub your hand along a table. The table opposes the motion of your hand. This is called friction. Put some washing up liquid on the table (not too much!!) and try again. What is the difference? What happens to the friction between your hand and the table?

Condensation can happen in one of two ways. Either the air is cooled to its dew point or it becomes so saturated with water vapor that it cannot hold any more water. The second case is what occurs inside the mask. We’ve all had a soggy mask when we leave it on a long time!

But that’s not all that’s going on in the simple face-mask! There are some important chemical forces at work, read on….

Apart from friction and condensation, some chemical forces also help masks to trap particles. Once a particle comes into contact with the filter fibres of the material in the mask, it becomes stuck due to Van der Waals Forces. Van der Waals forces is the name given to a weak electrical force which attracts particles to each other when they are close together.

Particles become trapped in the mask due to four
different physical and chemical phenomena

A mask’s fibres will have areas that are slightly negatively or positively charged. This is called polarity. Most particles a mask will filter will also have this polarity and therefore particles are attracted closer to the fibres. Water for example is a polar molecule. Van der Waals are weak forces, but combined with friction the particulates will become trapped between the rough mask fibres and are prevented from flowing through the mask in both directions.

Extra optional activity on Van der Waals forces: . – simple experiment to see the difference of Van der Waals forces, versus hydrogen bonding.

Electrostatic Attraction

N95 mask (thanks to J. J. Castellon, Unsplash.com)

A mask can also use electrostatic attraction to filter particles. An electro-charged material is added to the fibres and this attracts oppositely charged particles which stick to them. N95 masks are made with such characteristics and can filter 95% of airborne particles. They are only necessary for doctors and nurses in medical settings.

Testing the efficacy of homemade masks

To summarise, our masks use condensation, friction, Van der Waals and Electrostatic attraction to protect us and other people from airborne particles, including Covid-19.

A word of caution, masks with incorporated valves don’t protect those around you, as they only filter air for the user, but allow all their unfiltered air outward.

( Most of the text above is taken from the video below)

Extra activity to suggest: Try to observe some of the mask material fibres under a microscope in your school and compare different masks and fibre diameter sizes.

6. Conclusions – What worked best?

What are your conclusions on how masks work? Was your hypothesis confirmed? Do you think they are an effective way to control Covid-19? Explain.

What do you now think about the whole mask wearing debate? How do you feel about wearing them or others wearing them or not, around you or your family? What could help to convince them that they work?

4. Alice Hamilton and the story of the face mask

Alice Hamilton (February 27, 1869 – September 22, 1970) was an American physician, research scientist, and author who is best known as a leading expert in the field of occupational health and a pioneer in the field of industrial toxicology. Hamilton trained at the University of Michigan Medical School. She became a professor of pathology at the Woman’s Medical School of Northwestern University in 1897. In 1919, she became the first woman appointed to the faculty of Harvard University.

Her scientific research focused on the study of occupational illnesses and the dangerous effects of industrial metals and chemical compounds. In 1905, she published an article in the Journal of the American Medical Association, reporting on experiments measuring the amount of streptococci bacteria expelled when scarlet fever patients cough or cry. She also measured the strep bacteria from healthy doctors and nurses when they talk or cough, leading her to recommend masks during surgery.

In addition to her scientific work, Hamilton was a social-welfare reformer, humanitarian, peace activist, and a resident-volunteer at Hull House in Chicago from 1887 to 1919. She was the recipient of numerous honors and awards, most notably the Albert Lasker Public Service Award for her public-service contributions. (Sources: )

7. What did you like, what did you learn?

What did you most like/least like about this activity? 

What did you learn about the science of how masks work?

Are you curious to know anything else about this topic?

Leave a comment on how you liked this activity, on our twitter @SophiaPhysics

8. Sources and Extra Resources 

HSE advice on how to wear a face mask properly

A guide to face masks

A brief history of medical face masks

Corona Virus – New Facts about Infection Mechanism (NHK documentary video)

The Forgotten Science behind Face Masks

Every Monday and Thursday Professor Luke O’Neill from Trinity College Dublin, explores the world of science on the radio – here is the link to the Podcasts: https://podcasts.apple.com/ie/podcast/science-with-luke-oneill/id1460682290

Science Vs. Podcast – The Mask Wars