Archive for the ‘Physics’ Category

“How do you sink an orange?”, and other floating and sinking conundrums…

If you follow us on Twitter, you may have been racking your brains over our recent science pub quiz question, “How do you sink an orange?” Read on…



‘Floating and Sinking’; that well-known chestnut of primary science experimentation. I suspect this is one experiment that many teachers dread, for fear of flooded classrooms, sodden literacy books and angry parents demanding to know why little Tarquin has come home with a soggy jumper. To be fair, this is wholly understandable- it takes more than a faint heart to give 30+ children carte blanche with tanks full of water!

However, it really is worth avoiding the concomitant temptation to make floating and sinking experiments entirely teacher-led. In my experience, trusting the children (and telling them that you are trusting them), along with clear ground rules, really do pay off, and if you make the experiment interesting and pacy enough, most children shouldn’t need to resort to splashing.


if you can find one, a fishtank is good to use at the front of the class, for ease of viewing through the clear sides (chat to the caretaker, most schools seem to have the relics of a failed aquarium somewhere). However, the disadvantage is that they are very heavy and awkward to move when full of water. A cheaper, easier and still effective container is a basic clear plastic box, the kind that staffrooms/store cupboards are full of. (I temporarily emptied out some Spanish resources to pinch the boxes for an afternoon). It’s good to get as many as you can of these, my personal preference is to have 4 or 5 groups with a ‘tank’ each. This means they can all see, all get chance to have a go, and hopefully stay more engaged.

If you’re really not sure about having several tables running the experiment at once, this could be a one-group-at-a-time activity . Many KS1 classrooms have a water tray, KS2 classrooms could even try to pinch one of these for a lesson.

When it comes to choosing objects for conducting the experiment with, it’s good to try and deviate from the obvious examples. Yes, you want some easily predictable ones in there, but try and maintain interest (and stretch the more able), by bringing in some more unexpected objects, that might not react as they expect… you could even pick a silly object like a pineapple, a toy or somesuch – maybe not the most scientific on the surface, but it keeps the experiment fun, keeps the kids talking and you’d be surprised how these things can actually spark off scientific conversations


1) A paper clip

2) a heavy rubber ball, about the size of an orange.

3) an orange

4) a biro

The ball and the orange are an interesting pair. If you pick a dense enough ball, it should sink, while the orange will float. This is due to the orange’s air-filled, pitted skin, but it’s good not to explain this; If anything, leave it open for talk partner time, or a possible extension to the investigation…


Plasticine is a great material to use for floating and sinking, and to introduce surface area/density. A small, dense ball of plasticine sinks, but a boat or raft shape will float; as an extension, let the kids investigate the different shapes – what will they have to do to make it float? Why does it work?


So, we’re left with our orange conundrum. Next, take a single segment of orange and ask the children if they think it will float or sink. As it is smaller, and part of the same fruit, most will predict that it too will float. Drop it in, and watch the perplexed faces as it sinks! Get the children talking about what the differences might be, and why a smaller object sinks when the bigger one floats. A next step is to give the children an orange in each tank and ask them to make it sink. They will see that even holding it under water doesn’t make it sink for long, as each time it bobs back up. They should hit on the idea of peeling it and segmenting it. Can they work out what the most important thing they did was? You could demonstrate how the peel works by putting a ball in a rubber ring – it’s essentially the same effect.

As a further extension, you could even give each group a whole, peeled orange and see if they can get it to float again. we did this immediately after the plasticine boats experiment at a science club, and it was really interesting to see them synthesise their knowledge. Some children tried to place it on a boat or raft, some tried to spread the surface area by segmenting it and then placing it on a raft, while others tried to make a plasticine ‘peel’ for the orange. All of the ideas were valid, even if they didn’t work, and all the kids were having great’ science talk’, a key facet of the new curriculum.


So, in conclusion, I guess my main point here is “don’t be afraid to experiment and risk a few splashes”! Deviating slightly from the standard, safe options into more child-led learning will give some great results. Now, which other fruits can I try to sink? Next on the list is a kumquat…


Space Topic

This post will cover a recent Space topic delivered to Y5. The topic included; the planets of our solar system, relative sizes and distances of the Sun, Earth and Moon as well as the orbits of the Earth and Moon. We will focus on key parts of the topic here.

The above picture shows the display for this topic and as you can see it includes visually stimulating pictures, questions, children’s work and books for them to look through. Children are encouraged to bring in items from home to add to it and can be rewarding using whatever system you have going; team points, class currency etc. Two of the books in the above picture belong to children and one child brought in a piece of meteorite although this wasn’t on display at the time this photo was taken.

photo (2)

Hook them in

To hook the children into the topic, they were introduced to it as a ‘space explorers’ returning to earth after investigating the universe. The video used showed space starting from deep space and heading towards Earth. This really engaged the class at it used space’s ‘awe and wonder’ features nicely.

Kinaesthetic Approach

To increase pupil’s scientific thinking it is best to get them to see things for themselves. This undoubtedly raises some issues for space and until NASA launches school trips into space we need to improvise. A successful, interactive session for space was to use different sized objects to represent the Sun, Earth and Moon; I displayed a selection of spheres including a beach ball, football, tennis ball, small bead and blue tac as small as possible. Because not all schools have beach balls, a football could represent the Sun which means the Earth would have to be a small bead and the Moon would be the tiny piece of blue tac. The children had fun discussing these differences and then sending the volutneer ‘Sun’ out of the classroom door and 12m from our volunteer ‘Earth’ to show its relative distance.

Another interactive session was ‘plasticine planets’ where the children, after an input on orbits, were put into groups and demonstrated orbits using plasticine balls, string and pins. This was a challenging activity but they all managed it with regular learning stops, asking everyone to look at particularly successful groups. LAPs were asked to demonstrate the Earth’s orbit around the Sun, AAPs were asked to demonstrate this AND the Moon simultaneously orbiting Earth. The HAPs were challenged to explain how we get varied seasons and given Ipads with model solar systems on to research this.

Assessment quickie

The above work was my favourite piece of assessment showing the children’s understanding of relativity between the Sun, Earth and Moon. After the practical lesson on the relative sizes and distances, strips of paper were given out; A4 cut into thirds, long ways. The children were simply asked to show what the Sun, Earth and Moon looked like in space. As you can see from the pictures above, you get an idea of which children understand that the Sun in much larger than both the Earth and Moon and how close they are relative to each other.

photo (1)


Thought Provoking Questions

It’s also important to set questions that make the children think and learn for themselves. The above question challenges pupils to investigate what the Sun does if it doesn’t ‘move across the sky’.

This post was an overview of the space topic taught to Y5. A more detailed description of each session will, in time, be added to our resources section so if this post interested you then keep your eyes peeled for the resources or if you can’t wait, request more information below.

Considering Birds

My continuing adventures in the natural world

The Garden Smallholder

Small-Scale Smallholding, A Tiny Farm In A Big Garden

The Dragonfly Woman

Aquatic entomologist with a blogging habit

Beetles In The Bush

Experiences and reflections of a Missouri entomologist