Demonstration for surface area to volume ratio

So, surface area to volume ratio is a common concept in Science…

In digestion, they learnt that food are broken into small pieces so that it has larger surface area to volume ratio for enzymes to work on.

But, it’s hard to student to grasp the concept. They don’t get it how food in smaller pieces have larger exposed surface area to volume ratio.

So, here’s a simple demonstration.

First, make 2 jelly using red cabbage (reason being it’s a natural pH indicator) with identical moulds. Cut only 1 of the jelly into quarters. Then, add them into container of equal volume of lye water (alkaline solution).

Due to red cabbage being natural pH indicator, the jelly will change colour in alkaline solution (yellow in strong alkaline). As seen, the jellies cut in quarter turned yellow faster than the larger jelly because it has larger surface area to volume ratio.

2 jellies using identical mould. Only 1 jelly is cut into quarters.
The results of the demonstration.

Lesson on haze or air pollution

Demonstration set of haze/ air pollution

Creating haze in a beaker.
1. Measure and prepare aluminium foil to cover beaker.
2. Light up wooden splint and drop it into a beaker.
3. Cover with aluminium foil.
4. Place ice on it.

Possible extension:
Use white paper towel to wipe the inner surface. Students will be able to observe very fine soot

Possible changes, use leaves and soil as a close set-up to forest. But didn’t work too well when I tried. Leaves must be really dry to burn/catch fire.

Heat demonstration

Kids were amazed with convection demonstration today.

They went “wow” when they saw the red dye reversed its direction. Love their expression! If only I could snap a photo of their wide-eyed reaction. hahaa.. This is why I enjoy doing demonstration 🙂

The kids also had fun with a “magic liquid”.

They kept asking me where to buy it and I was like… I don’t even know what this “toy” is called to google to buy it.

Also did metal ball and metal ring, but not much excitement as these two demo.

Red cabbage indicator

My favourite demo for the chapter on acid and alkali is…

red cabbage indicator

Add a pieces few leaves of red cabbage into a beaker of hot water. The leaves will decolourise and the solution will eventually turn purple. We will use this solution as the indicator. Add 2 drops into different samples and observe for colour change.


Colourful results from red cabbage indicator

Here’s my colourful result using these samples (from yellow, clockwise)
Lye water, bicarbonate of soda, sprite, detergent, lemon

Best used with samples that are colourless.

You can encourage students’ participation by allowing them to bring their own samples. Students generally are more excited to work on stuff that they contributed.

You can also extend this activity by giving them time to make their own indicator paper which they can bring home. Simply cut strips of filter paper, soak it in red cabbage juice and let it air dry. Students can then use them by dipping it into samples.

Sources of light

To introduce to students that light is a form of energy, I usually highlight some examples of energy changes to light energy.

Here are some stuff I use for to demonstrate the energy conversion…


Different sources of light energy

Dynamo torch (bought on Carousell):
Kinetic energy to to electrical energy to light energy light energy

Solar chasing light (bought in Kmart, Australia):
Solar energy to electrical energy to light energy

Light bulb:
Chemical energy to electrical energy to light energy

Chemical energy to electrical energy to light energy