Sciences: what is a cross-sectional study?

Tutoring science, you might encounter experimental design. The tutor mentions the idea of a cross-sectional study.

cross-sectional study:

Let’s imagine a characteristic of interest, C.

In its simplest form, a cross-sectional study will select two groups – group A with characteristic C, and group B without it. Then, the investigators will measure other characteristics of the groups, wondering if the presence or absence of the others is connected with the lack or presence of C.

Except for the absence or presence of C, the members of groups A and B will be similar.


Carlson, Neil R. Discovering Psychology. Needham Heights: Allyn and Bacon, 1988.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Science: what is sublimation?

Tutoring science, you cover changes of state. The tutor defines sublimation and relates an example.

Sublimation means the change from solid to gas state without becoming liquid in between.

In everyday life, sublimation is seldom observed, but there is a great example I heard from a science teacher in elementary school:

Imagine hanging clothes to dry outside on a bright, cold winter day when it’s -10°C. At first, the clothes will freeze on the line. Yet, after a few days they will be dry, even though the temp has been -10°C the whole time. Obviously, the water in the clothes couldn’t have thawed, then evaporated. It could only have sublimated (aka sublimed).

To appreciate the anecdote above, it helps to have lived in a place with cold winters where, even then, people hang their laundry to dry.


Mish, Frederick C. (editor). The Merriam-Webster Dictionary. Springfield: Merriam-Webster, 2004.

Mortimer, Charles E. Chemistry, sixth edition. Belmont: Wadsworth Publishing, 1986.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Physics: what is parallax?

Tutoring physics or general science, the term parallax might arise. The tutor gives a definition.


the phenomenon that the position of an object seems to change as the viewer’s location changes.


Gilmour, Lorna (ed). Collins Essential Canadian English Dictionary & Thesaurus. Glasgow: HarperCollins, 2006.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Science, Climate change: the albedo effect

Tutoring high school science, you may be asked about the albedo effect. The tutor explains it simply.

Albedo means loss of incoming radiation due to reflection. Light and heat are examples of radiation (see my previous post).

Regarding Earth’s climate, the albedo effect refers to the idea that sunlight that reflects from Earth doesn’t heat it. The greater Earth’s albedo, the less heat Earth absorbs from the sun. If Earth’s albedo decreases, it will absorb more of the sun’s rays, so will heat up. This is the simple way of applying the albedo effect.

Polar ice caps, covered in white snow, are quite reflective. However, as the ice caps melt, they expose rock and ocean, which are potentially much less reflective. Hence, Earth’s temperature could rise from the melting of the ice caps because of a corresponding reduction of the albedo effect.


Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Science, physics: what is radiation?

Tutoring science, the concept of radiation arises. The tutor explains it.

Radiation is electromagnetic energy travelling from its source.

Imagine a radio receiver which you can tune to any frequency. Actual radio station signals will be at the low end, then microwaves, then heat (aka infrared), then visible light. Past visible light is ultraviolet light, then X and gamma rays.

Radiation of higher frequency has higher energy. X and gamma rays have such high energy they can pass through solid objects.


Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Cooking: temp of a warm object

Cooking means constant self-tutoring. The tutor speculates about the actual temperature of a warm object.

Yesterday I took a glass casserole dish of mac and cheese from the oven. Its baking temp was 177C.

An hour later, most of the mac and cheese had been served from the dish. Moving it, I was surprised how warm it still was to the touch.

Yet, how warm was it? I didn’t have a convenient way of measuring, so I opened a browser tab and found, whose members seem to agree that about 60C is dangerous to touch for more than a second or two.

The casserole dish wasn’t hot; rather, just surprisingly warm. I’d estimate it was about 40C.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Botany: black walnut: juglone

The tutor researches the effects of juglone from black walnut trees.

Juglone is a toxin produced by the black walnut tree; it’s found throughout the tree and in its leaves, shells and nuts.

Apparently, to humans eating the walnuts, the juglone is not a problem. However, it enters the soil from the roots of the black walnut tree, as well as from its leaves, twigs, and even pollen falling to the ground – not to mention the nuts and their shells. Some plants, such as tomatoes, potatoes, lilacs, and rhododendrons, can be damaged by the juglone.

To be safe, composted matter from black walnut should wait a year or more before application.

Horses are particularly sensitive to juglone; neither black walnut shavings, nor the husk fibre, etc, should be used in a horse’s environment.


Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Stainless steel: magnetic or not?

The tutor investigates the idea that stainless steel is non-magnetic.

I’ve heard from more than one source that stainless steel is non-magnetic: if you put a magnet to it, there isn’t attraction like you might expect with “ordinary” steel.

According to Scientific American, some stainless steel is magnetic, but the most common kind (Type 304) isn’t. What makes Type 304 nonmagnetic: its content of nickel, manganese, carbon, and nitrogen.

Stainless steel made from just iron and chromium (13 to 18 percent Cr) likely will be magnetic.

The presence of certain elements in the steel affects its atomic pattern; some patterns result in magnetic attraction, while others do not.


Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Biology: protists: diatoms

The tutor mentions a few points about diatoms.

In my Feb 4 post I introduced protists, which constitute a kingdom of eukaryotic, mainly single-celled organisms. Protists are divided into plantlike and animal-like ones.

Diatoms, from phylum Chrysophyta, are among the golden brown algae. They are plantlike protists, perhaps the most numerous of them. In the oceans, their abundance makes them a major food source at the base of the ecosystem. Furthermore, they are prominent producers of oxygen on Earth.

Diatoms have a two-valve structure, rather like the base and lid of a box. They are well known for having glass (silica) in their cell walls, which show striking patterns under a microscope.

Diatoms have been even more abundant in the past; today, those fossils constitute diatomaceous earth, which is mined for applications such as soundproofing, filtration, and scouring powders.



Mader, Sylvia S. Inquiry into Life, 9th ed. Toronto: McGraw-Hill, 2000.

Ritter, Bob et al. Biology. Scarborough: Nelson Canada, 1996.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Physics: models of the atom

The tutor reviews the progress of thought about atoms through the ages.

Democritus, a Greek philosopher living around 400 BC, is credited as the first promoter of the concept of the atom. He proposed that all matter consists of tiny, indivisible particles, which he called atoms.

The next published refinement of Democritus’s idea was Dalton’s atomic theory of 1808. He agreed with Democritus, elaborating the idea of an element – a type of atom. Every element has its unique type of atom.

After further study came the Thomson model, in common use from the 1890s to 1911. It was also called the “plum pudding model”, and proposed that an atom consists of positively charged “dough” with negatively charged “raisins” scattered throughout. Thomson, who discovered the electron in 1897, realized that the electrons should be moving.

Rutherford, in 1911, carried out an experiment whose results led to the idea of the nucleus. The Rutherford model claims that the center of an atom is heavy and positive, while electrons orbit distantly around it. Most of the “volume” of an atom is empty space between the nucleus and the electrons.

The Bohr model (1913) refined the Rutherford model, suggesting that the electrons orbit at only certain distances (levels) from the nucleus, and that they can jump from one level to another. The levels are called shells.

Rutherford’s model is still used until high school; in grades 11 and 12, Bohr’s is studied.

In a future post I’ll explain Rutherford’s experiment and why it led to such a breakthrough.


Giancoli, Douglas C. Physics. New Jersey: Prentice Hall, 1998.

Bullard, Jean et al. Science Probe 10. Scarborough: Nelson Canada, 1996.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.