## A nice Pressure in Liquids question

Posted: December 6, 2013 in Institute of Physics, Thoughts and ideas
Tags: , , , , , , , , , , ,

I first was introduced to this really nice question by Neil Atkin (@natkin) and ever since I have tried to find a good way of showing it. So, look at the question and the explanation that I think is correct, as far as I can tell (but please point out any faults in my reasoning). Then, check out the simple demo I used to show this.

“If I am on a boat in a pond and I hold a 10 kg rock in my hand, what will happen to the level of the water if I drop the rock inside the pond? Will the water level increase, stay the same, or be lower?”

It’s all to do with Archimede’s Principle that states that the upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid displaced by the body.

This should help us think about this problem. In fact, if the boat is floating it means that the weight of the water displaced by the rock when it is inside the boat must be the same as the weight of the rock itself. That is because the upthrust balances the weight of the boat, myself and the rock, or the boat would sink. So the rock displaces a volume equivalent to the space occupied by 10kg of water, i.e. 10 litres.

When I throw the rock inside the pond the water displaced by the rock is only the volume of the rock itself, which is most likely not 10 litres, but much less. So, the level of the water in the pond decreases!

I took these two photos before and after to convince you of this (the measuring cylinder we used in another attempt was to big to appreciate the difference). Click on either photo to enlarge them and see them in Gallery view.

Advertisements

Anyone who insists technology is disempowering has probably not come across really young learners interacting with it. Today I was reminded about how intuitive, engaging and formative technologies like the iPad really are.

I want to call Nonna!

My 2 year old boy, Martino, felt like talking to Nonna (grandma in Italian). I say talking, but, although he can say quite a few words, he hasn’t learnt to say many sentences yet. What he has learnt to do, and very quickly, is to use an iPad. In fact, he’s so good at it that today he ran in the kitchen, took the iPad Mini and came back to the sofa looking pleased with himself. Then, he turned it on, swiped to access the apps, found FaceTime inside a folder and called my mum from the recent calls. When Matteo (my eldest) heard the ringing sound of FaceTime he asked Martino, if he was calling Nonna. “Sí, Sí!” answered Martino.

Needless to say that this unexpected call made my mum’s day, but what I’ve witnessed today, and many other times since Martino was one and a half, is something that made me think deeply about the power of technology.

Our learners are deeply engaged with technology, they grow surrounded by it and naturally embrace it as part of their learning. I believe it is essential we engage our students with technology to harness this enthusiasm our young people show for it. I heard of many primary and secondary schools that began to use iPads when they noticed their youngest learners kept touching the screen of PCs and laptops the first time they used them. iPads, smartphones and tablets are engaging and an integral part of many learners’ every day routines. They are drawn to them and naturally interact with such devices with great interest and proficiency, so using them in the classroom seems to me to be a logical way to engage children in their learning. This will make schooling more fun, but that should never be the driver for integrating technology in the classroom! iPads and other technologies open ways to redefine pedagogy and learning experiences. They empower learners and teachers, so that students become more independent and creators of knowledge, rather than simply consumers of knowledge. Let’s embrace technology for the right reasons and not thinking that the kit will solve all the teaching and learning challenges in our schools.

There are many ways to use technology creatively and innovatively to enrich our learning environments and much can be learnt from educational blogs such the CollaboratEd.org.uk Blog (@Collaborat_Ed), Neil Atkin’s Blog (@natkin), maybe this Blog you are reading and, one of my favourite, Gavin Smart’s Blog (@GavinSmart).