## Introduction: STEM Clubs Simple Experiments

In this Instructable I will show you how to make STEM related activities that you can do with students at your school. You can use them in your lessens or in a science cubs. Some of the activities I designed myself, and of them are upgraded versions of the experiments that I did when I was in school.

Here are the experiments/activities:

1. Cardboard Sundial

2. Balancing potato

3. Cubic bubbles

## Supplies

Sundial:

- cardboard

- sellotape

- color markers

- scissors

- protractor

**Balancing Potato: **

- cocktail sticks

- potato

- two spoons

**Cubic bubbles: **

- plastic straws

- scissors

- blu tack

- cocktail sticks

- wash-up liquid

- water (distilled if possible)

- baking powder

- corn starch

## Step 1: Cardboard Sundial - Theory

**Types of Sun Dials**

The sundial consists of the gnomon and the dial plate and it must face North. Here are three most common Sundials:

**Horizontal** - The dial plate is horizontal and facing North, and the gnomon rises at an angle equal to the sundial site's latitude (usually found in gardens)

**Vertical** – The dial plate on vertical and the gnomon is fixed at the angle of the site latitude (exactly like horizontal Sun dial). Ideally vertical Sundial plane must face south and because it’s placed vertically (usually on the building walls) the shadow doesn’t move uniformly. The formula for dial hour angle:

tan(Θ) = cos(Φ)tan(15* x ω)

**Equatorial** – The dial plate is fixed in the plane of equator and facing North and the gnomon is perpendicular to the dial plane (usually found in parks) The hour lines are spread equally at 15* intervals (t is time difference between 12 noon and time on your sundial in hours)

Φ = 15* x (t)

**Math behind our Horizontal Sundial: **

The formula for calculating the hour lines Θ (theta) on a horizontal sundial is:

tan(Θ) = tan(ω) x sin(Φ)

where:

Θ = the resulting dial hour angle measured from the noon line (- is left of the noon line, + is right of the noon line)

ω = the hour angle of the sun from the noon meridian, expressed in (+/-) degrees. The hours are minus in the morning (ante meridian) and positive in the afternoon (post meridian).

Φ = sundial site latitude, in degrees

We need to determine the dial angle theta for each hour angle ω of the sun. We measure ω using the meridian as the reference. At 10:00am, the sun is 2 hours before the meridian. At 03:15pm the sun is 3 hours 15 min after the meridian.

Since the earth rotates 360 degrees in 24 hours, that's 15 degrees in 1 hour. So 10:00am can be expressed as the hour angle of -2 x 15* = -30* (Notice the minus sign). At 03:15pm, the hour angle is 3.25 x 15* = 48.75* (Notice this is positive).

## Step 2: Sundial - Assembly 1

The attached template is designed for Manchester, UK latitude (53.5*) but it will work OK for latitudes +/- 10 degrees. I have also attached the .svg file that you can edit in free software - Inkscape and change the angle to your city latitude.

- print the Sundial template on card (160gsm - 220gsm)

- use pre-calculated values (for 53.5* latitude) and draw hour lines by marking them precisely with protractor

- cut out your sundial and gnomon; don't forget about decorations, most sundial have Sun and some basic information like location and maker name

NOTE: I also uploaded templates and calculated angles for latitudes from 20 degrees to 70 degrees. At the equator and north/south pole this sundial turns into equatorial sundial with vertical gnomon and evenly spread hour angles (every 15 degrees). Please choose template closest to your latitude and enjoy making your sundial :)

## Step 3: Sundial - Assembly 2

- cut out the gnomon and fold card where the dotted lines are

- use sellotape to tape two pieces of gnomon together

- Tape assembled gnomon to the Sundial plate making sure it's in the center of 12 noon

- use compass or smartphone app to find North (so gnomon is pointing celestial north) and position your Sundial

NOTE: Remember that Sundial will show you real solar time and 'it' doesn't know about daylight saving so please bear in mind that depending on when you test your sundial it might be off by one hour. It's a good discussion topic with students and I found out that this activity is also great for practicing protractor skills especially for younger students.

## Step 4: Balancing Potato - Theory

The center of gravity is the average location of the weight of an object (imaginary point in a body of matter where the total weight of the body may be thought to be concentrated).

The location of a body's center of gravity may coincide with the geometric center of the body, especially in a symmetrically shaped object composed of homogeneous material. An asymmetrical object composed of a variety of materials with different masses, is likely to have a center of gravity located at some distance from its geometric center.

When you try to balance an object the point of support (pivot point), should be on the same vertical line as the center of gravity. Then the object, no matter what shape, is going to balance. It will be stable if the center of gravity lies below the pivot point. If the center of gravity is above the pivot point, even a slight disturbance will pull it off balance.

In this experiment the center of gravity of this assembly has to be below the pivot point. The pivot point is where the toothpick rests on the rim of the glass. The actual center of gravity must lie in the empty space between the two forks and below the pivot point to achieve stability.

## Step 5: Balancing Potato - Assembly

- cut potato in half (one half will bu used as a base and the other half for balancing toy)

- put two spoons on each side of half-potato at the angle about 45 degrees, remember to point the spoon slightly down (if done with older students you can use forks which are easier to put in)

- put cocktail stick in the middle of the half-potato

- with your finger try to find the balancing point of potato with spoons by trying to lift it with your finger at various points along the cocktail stick

- put another cocktail stick into the second half of the potato

- now when you know when the balancing point is exactly you can try to place the potato with spoons on another cocktail stick (it's quite easy after a little bit of practice as you can see on picture above)

Note: You can set up challenge for students asking them to balance the tip of cocktail stick on tip of another cocktail stick (it's slightly more tricky but definitely possible as seen on picture above).

Here is video of potato in action :) https://youtu.be/ZJAxZ7Yn504

## Step 6: Cubic Bubbles - Theory

No matter how many times you blow a bubble, it always ends up round. This is because the molecules in the bubble mixture pull on each other, which means that you end up with a shape that has the smallest amount of surface (a sphere).

In this experiment a bubble is surrounded by other bubbles, these side bubbles push against the center bubble, squishing and squashing until it has corners and sides and looks like a cube.

Thin-film interference occurs when incident light waves reflected by the upper and lower boundaries of a thin film interfere with one another to form a new wave. The iridescence of a soap bubble stems from light striking the bubble from varied angles.

The path length varies with the angle of incident light, giving varying path differences for the internally and externally reflected rays at different points on the bubble. This means that, even if the soap film is of uniform thickness, different colors can be seen.

## Step 7: Cubic Bubbles - Assembly 1

- pick 8 straws

- cut 8 straws to same size (keep the bendy bit)

- cut small slit in each straw (about 1cm)

- fold the end with slit and push it inside the end without the slit in order to make a square

- prepare two of these squares

## Step 8: Cubic Bubbles - Assembly 2

- you will need two squares (made in previous step), 4 straight sections and 4 cocktail sticks

- pierce cocktail sticks at each of the four corners

- put small straight sections on cocktail sticks

- mount second straw square by piercing it through cocktail sticks

- secure each of 8 corners of the cube you just made with small amount of blu tack (this will improve integrity of your construction)

## Step 9: Cubic Bubbles - Bubble Mix

Bubble mix recipe:

- 6 cups of water (distilled if possible)

- 1 cup of wash-up liquid (the results will depend on brand of wash-up liquid unfortunately, so I recommend to test few different ones on small scale)

- 1/2 cup of corn starch

- 1 tablespoons of baking powder

Mix it the bowl deep enough to immerse the straw cube you made. Now you have to slowly and carefully immerse all 6 sides of the cube and once you succeed the small cubic bubble will form inside. Here is a video showing best technique to achieve that:

NOTE: You can ask students to experiment and create different shapes and see what kind of bubbles they can make.

First Prize in the

STEM Contest