Constants for Experimental Design

[Stephen Snider]

Hey all!

I'm having trouble coaching my students concerning constants. We understand the difference between controls and constants (I think - lol), but besides the basics like gravity and the speed of light (when these make sense per the prompt), what constants might you think of for something like a solubility prompt or something regarding acids and bases? 

Seems like low hanging fruit, but our team defaults to "the measure of a second" whenever time is involved or "the measure of a cm" in the event we are measuring distance, but get dinged points for this. 

For solubility... In the event we are only given water, would that make water as the solvent a constant? Since we can't choose another solvent, that wouldn't then make it a control?

For acids and bases... Would be pH be a constant? How would logarithmic units then be different then using seconds or cm?

The other day we did a Hooke's Law prompt... If you have one spring k might be a constant, but if you have several to choose from, then wouldn't it actually be a control since you're choosing a particular spring to work with from among several different ones?

Any guidance would be much appreciated! Thank you!

-Stephen

[Narayan S. Raja]

On Mon, Jan 27, 2025 at 4:40 PM 'Stephen Snider' wrote:

> what constants might you think of for something like a solubility prompt or something regarding acids and bases?

Constant = something you have no ability to change, e.g.,

pH of the given water sample, or room temperature.

Controlled variable = something you do have the ability to change,

but keep unchanged: e.g., you choose the same solute for all the

solubility experiments, choose the same volume of solvent, etc.

> The other day we did a Hooke's Law prompt... If you have one spring k might be a constant, but if you have several to choose from, then wouldn't it actually be a control since you're choosing a particular spring to work with from among several different ones?

Gravity, or coefficient of friction, might be constants in this case.

Given multiple springs, using only one of them would make that

a controlled variable (same spring).  If timing is being done by 

a human being clicking a stopwatch, having the same human 

do the timing for all the experiments would make that a

a controlled variable,

[Mrs. Demir]

Disclaimer: not an expert here.

Instead of "measure of a second" I would add something like "which is the time it takes for a certain number of osillations of a cesium atom". Instead of "measure of cm", I would use definition of meter as "the length of the path travelled by light in vacuum during one osillation of a Cesium atom".

For solubility experiments solubility constants of the solute could be used. Kw for water or Ka or Kb for acids and bases can also be used as constant. 

For spring experiment, I'd use Earth's gravitational constant, g, as the safest option. If you used one spring, the type of spring would be a controlled variable across the experimental and the control groups (avoiding k being the controlled variable if especially the experiment involves heating of the spring as temperature would change that value). The value of k (which may or may not be given), however, would be a constant for the experiment if only one type of spring is used (again assuming no temperature change is involved). 

In reference to " For solubility... In the event we are only given water, would that make water as the solvent a constant? Since we can't choose another solvent, that wouldn't then make it a control?".... I define control as "the reference experiment" whereas constant as "a numerical value universally accepted as not changing". So in your example, water is your control and cannot be a constant. A numerical value such as Ksp of the solute can be used as the constant.

--
You received this message because you are subscribed to the Google Groups "Science Olympiad Coaches" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ScienceOlympiadCo...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/ScienceOlympiadCoaches/CACd7euemhLEE-uNxg_EJ0YV692TCZpHT2CAxE%2Bzk87VZqtXTbQ%40mail.gmail.com.