Posts Tagged ‘Forces’

It can be tricky to find good examples to show how forces add up to give a resultant force. In particular, sum of vector forces in AS Physics is something that takes practice in order for students to grasp. So, when one of my boys enjoyed a ride on one of those trampolines where they strap you to two elastic ropes to make you jump very high I thought it would be useful to share this photo with you. The tensions from the two ropes pull him at the same angle on either side, but he jumps up vertically. Why does this happen? You can ask students. Then force arrows could be drawn and look at their vertical and horizontal components to see that the horizontal components are balanced and the vertical components add up, etc…

What other useful concrete examples do you use with your students?


Sorry the photo got uploaded on its side instead of the right way up, but you should be able to easily rotate it on a PPT presentation, or you could mess with you students and tell them it was taken at the Equator 😀 and see what they say!

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.

I was really privileged yesterday to find myself as one of the Judges of the First Campus Hands On Science “Science RAPs” competition. The event was opened by a fantastic Rap created by John Chase with a video in the background created entirely using Science Photo Library images and videos. The way John represented Science in his Rap and the fantastic integration of images and videos edited by Alison Somerville of Photo Library made the whole experience quite Magic!

Then, it was time to watch the video Raps entered by learners from various schools. All entries were really inspiring and entertaining. We had entries from Howell’s School (Llandaff), Whitchurch High SchoolTonypandy Community College and Gwauncelyn Primary.

So, the winners were in this order:

– Overall winner “The life of a star” by the White Dwarfs (Tonypandy Community College) with a fantastic and really scientifically sound rap on the life cycle of a star. I am sure this group learnt a lot by writing this rap and this topic will really stick!

– Runner up and highly commended ‘Nanotechnology’ by Dr Incy-Wincy + Mouse (Gwauncelyn Primary). This was a phenomenal entry. In fact, it was our only Primary entry, but the amazing Anas (Year 6) entered on his own and did all the recordings and editing. The Science in his video is really sound and the topic really interesting. Well done Anas, a great job!

– Best Entertainment Value (Whitchurch High School). This group of Yr9 pupils chose some really entertaining clips on forces and they really seemed to have great fun doing it!

– Best Original Analogy (Howell’s School). The “Fusion Love” rap from this group of girls in Howell’s was a really cool analogy between a love story and two nuclei that fuse (merge) in a nuclear fusion reaction.

Apart from the lovely trophy the winning school received, there were lots of really cool prizes for everyone. In particular the overall winners won a HD Flip Camera each. There were also shopping vouchers for the runner up and other great goody bags for everyone.

This was a really worthwhile experience for the learners who became so involved in their fantastic work, and not only for the prizes they received, but because of the learning process in the whole project!

It would be great to have more entries next year, so make sure you look out for the competition and send your entries in!