# On Density

Density is one of those topics that science classes frequently include – especially in the physical sciences. Yes, it’s the ratio of mass to volume – or as I like to think – how much stuff is contained in a given space.

Like any formula as D=M/V, given any two variables, it’s possible to calculate the unknown. Density is more than just working formulas – after all – it is an important concept to understand – but most teachers focus on density as it’s covered in a textbook or as their designated drills to pass a state-mandated test.

To me, it’s the application of density into our everyday world that gives the topic relevance. For instance, wood is more than just wood. Product information for a new fireplace or wood-burning stove may include information about softwood and hardwood.

Given 2 logs of the same size, the hardwood log (oak) will have more mass (think of it as heavier when you pick it up) than the softwood log (pine). There’s more wood substance packed into the given space as the same-sized log of softwood. Bottom line being that the hardwood log will burn longer and release more heat.

When density is applied to populations in biology, Hong Kong is very dense – just like hardwoods – well, more like ebony, one of the most dense hardwoods.

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Which is heavier, five pounds (kilos) or one pound (kilo) of water? That’s a no brainer – the oil is heavier, so will five pounds (kilos) float on one pound (kilo) of water? Sure it will because oil is less dense than water (Note: we could include a discussion about solubility, but will stick to density). Yep – that’s why we shake that bottle of Italian dressing before we use it.

Hot air doesn’t rise – (it never has and it never will) – but it is displaced upward by the colder air that is also more dense. (Here’s a past post that addresses that misconception). The same idea can be applied to any fluid (liquid and gases), so now density helps explain currents in the atmosphere and in bodies of water. https://afrankangle.wordpress.com/2012/08/08/on-hot-air/

You may remember the story of Archimedes (Greek mathematician, physicist, and inventor) whom the king called upon to determine if the crown was real gold or not. Legend has it that the explanation came to Archimedes while in a bathtub – “Eureka!” Of course, his points about density and displacement eventually led to how boats and ships float.

While at a party, you want a soda – which is found in a large metal tub. All the ice has melted, but the cold water is still keeping the cans cold. You notice some of the cans are floating and others lie on the bottom. The sign says Diet Soda and Regular Soda. You want a Diet soda, and density is telling you which one to pick.

Readers are wondering why I wrote this post – or at least what sparked the idea. After all, long-time readers here know I have reasons for what I do. I like Chex cereals – and earlier this year I bought a box of each of my favorites in the Chex family. (The written number represent ounces and grams.) Personally, I like the more dense one better – and it’s more filling – which should not be a surprise.

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# Flashbacks: On Science

I have a science background, but I pride myself in having understandable explanations. At least one of these will enlighten you. Enjoy, and I hope you comment on the post you visited.

# On Hot Air

Although we don’t mean to make generalizations inaccurate, they are not the full story. After all, these statements are, by definition, generalizations. Sometimes people generalize the generalization, but failing to remember that continual generalization moves one further from the truth – thus eventually turning the generalization into misinformation that leads to misunderstandings.

Repeat after me – Hot air does not rise.

Just to make sure, let’s try again – Hot air does not rise.

Regardless of the links you can provide to the contrary, or ever provide a reference for a reputable textbook, hot air does not rise – it never has and I very much doubt ever will. Yet, how many times have we heard or said, Hot air rises? (Yes, I cringe when I hear TV weather forecasters use it.)

Nah baby nah … hot air does not levitate. Hot air does not move upward on its own – It is pushed upward by more dense cold air that displaces it – Just has bathtub water level moves upward on the sides when one takes their seat in a bathtub. However, there is no need for you to run down the street naked like Archimedes yelling, Eureka, eureka, I found it!

Here’s the story. During my science teaching days, we were preparing a lesson for the next day. Because my colleague had not seen this activity, he took one set of the materials to the location of the ice machine – the boys’ locker room.

My colleague returned saying it worked great, but shared an interesting story. One of the physical education (PE) teachers watched without knowing any details, and then said, “This means hot air doesn’t rise.” Bingo! Meanwhile, this gave me an opportunity to have some fun with the good-natured PE teacher.

During the eventually discussion with the students after the activity – and knowing students would quickly deliver my comment – I stated, “If a PE teacher like Mr. X can figure this out on his own, surely this is easy to understand.”

We had fun with it through the years, for as students are so predictable. But the point remains the same – Hot air doesn’t rise because it is pushed upward when it is displaced by more dense, colder air.

By the way, here’s a similar activity – but ours was better. Yo, Starla, show Navar.

# On Generalizations

Generalizations are important because they are broad statements about a topic, many times involving related events. In education, making a generalization is a critical-thinking skill because the student must synthesize seemingly independent events into a generalized statement.

On the other hand and by the very nature, generalizations in themselves lack specific details, thus in life, people have the tendency to generalize generalizations, which actually takes them further and further from the truth.

Local weather reporters commonly use this generalization: Hot air rises. On its own, this statement implies that hot air moves upward on its own. Many people also commonly use this statement by focusing on the result, not the cause. For the record, hot air does not levitate. As air temperature rises, its density decreases, thus is displaced upward by denser, colder air that now occupies the space that the warmer air once occupied. Ah come on – don’t you remember the Archimedes story of being in the bathtub, and then running naked through the street yelling I found it!

Life is loaded with misconceptions based on generalizing generalizations that leads us to inaccurate and even incorrect information. Candy does not cause tooth decay, bacteria do; but sugar promotes bacteria activity. Human blood in the veins is not blue, it’s very dark red – yet the blue we see in our arms comes from the interaction of light with body tissues. Plants do release oxygen into the atmosphere as waste in one process, but plants also require oxygen for the same reason as animals.

These are just common examples of misconceptions that are rooted in generalizations. Imagine how many generalizations people misuse and misinterpret in topics as politics and religion. Politicians are masters of use broad, sweeping statements – some of which are accurate and some are not. Some are in the correct context, and some are not. Yet, whether we cheer or jeer the statement largely depends on our view of the one delivering the message, not our knowledge about the topic.

Not long ago, I listened to a pastor’s message to his congregation about creation and evolution. I know this topic is deep, yet I heard a person jumping from one generalization to another. I can only assume the pastor did this to get the message they wanted to deliver. On the other hand, the flock looks to the pastor for guidance and takes the pastor at their word, yet are unknowingly left with inaccurate information as their informational foundation.

The bottom line is simple: No matter the topic, there is a lot to learn about the world. Although new knowledge grows so fast, specialists find it difficult to keep up in their own field. It is difficult to sort through all the factoids in today’s world, thus the responsibility for learning continues to fall on the learner.