Which property of material is behind the leak proof bag experiment?

In this video, we tried the "leak proof bag experiment". This topic is in the theme Diversity, Lower Block Science.
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Opening and ending music pieces by Lynn Koo.
https://soundcloud.com/lynnkoo

Finding shaded areas of composite figures with circles (P6 Mathematics)

Take a look at this question:

This is a screen capture off a Facebook group and I do not know the original source of this question.

Anyway, let's try to do this question!

First you try it on your own, then you can check your answer by watching this video:

Finding areas of circles is a topic in Primary 6 Mathematics.
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Opening and ending music pieces by Lynn Koo.
https://soundcloud.com/lynnkoo

What is static frictional force? PART 1

Let's take a look at frictional forces without motion! This is part 1, as there's more to come :D This topic is in the theme Interactions, Upper Block Science.
Please consider subscribing to watch more!

Opening and ending music pieces by Lynn Koo.
https://soundcloud.com/lynnkoo