Posts Tagged ‘Physics’

Aaron was only 10 when he introduced me to WordPress and blogging. It is thanks to him that this blog ever started, so it fills me with joy to be able to blog again about another great achievement of his in the world of technology.

Now that he is 16 and in the midst of his GCSE exams, he has developed his first game for the iPhone/iPod. This was his personal project that he set himself over the Christmas holidays. He was not prompted by his ICT teacher, nor set this as a homework from school, just his own interest in coding and developing something good and rewarding.

You can find his game, which is actually really good and, in my opinion, stands up there with the big viral and highly addictive games like Doodle Jump, Angry Birds and Flappy Birds, here. RFLKTR is a really engaging game that uses mirrors you draw on the screen to guide a laser beam through gaps in the walls it encounters as it travels in space. This really interesting and stimulating feature of the game, which sounds easy, but believe me it is really hard, makes it a really engaging tool for Physics teachers when teaching Reflection of light!

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At the moment the game doesn’t seem to work on the iPad, but I am sure a later release will fix this and I would love to have other features of light that could be used to guide the laser beam across the screen. For example, it would be awesome to have blocks of glass and other materials of different refractive index appearing every now and again so that the player could move them in front of the incoming beam as well as changing their angle, so the beam can be refracted instead of reflected with these special items, etc…

Please shout out about this game and download it, because I believe learners who take their own initiative to create something like this deserve to be recognised for their effort and creativity!

You might have seen/done this one before, but the teachers I was showing it to found it quite useful, so I thought I would post it on talkphysics. The nodes and anti-nodes are a lot clearer when the amplitude of the oscialltions is higher, but I was told the signal generator broke the previous vibrator when set too high, so I was a bit cautious with this one.

There are several teaching and learning points with this demo. For example, you could get the students to calculate the speed of the wave along the spring, as we know the frequency from the signal generator and can measure the wavelength (for example by measuring the length of the stretched spring with a ruler).

Once we know the speed of the wave, we could ask the students to predict the next frequency in which a standing wave will form.

What else would you use this demonstration for? What other questions would/could you ask?

I was playing a new update of Doodle Jump on my iPhone this morning and I suddenly thought it would make a pretty cool lesson on motion and it could actually apply to both GCSE and AS Physics, depending how you phrase your questions.

The idea is to find out how high the little alien in Doodle Jump actually jumps. There is no reference in the game to suggest what scale the screen has, so I used Vernier Video Physics and arbitratily set the distance between the block on which the alien was jumping (see video below) and the last but one block above the creature to be 10m.

I then tracked the position of the alien for one jump and the analysis of the velocity graph shows the gradient is not right, i.e. g is not close enough to 10m/s2.

So, I went back and changed the scale to be 4.5m between the two blocks mentioned above. That seemed to have done the

trick, as the gradient of the velocity – time graph in the video below is about 10m/s2.

If you look back at the Displacement – Time graph for the vertical axis, you can now see that the little alien jumps to a height of about 2.3m. That is quite something for a little fella like him.

Obviously, we are assuming the alien is jumping near the surface of the earth, or at least a planet with the same g.

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 ūüėÄ and see what they say!

I recently was asked about the phases of the Moon and why the Moon appears to change in shape in its orbit around the earth. So I thought a good point to start from was to establish what misconceptions people have on this topic and I found this great video by Veritasium (but I would stop it at the end of the interview without revealing the explanation initially).

The most common misconception in the video seems to be that the earth blocks the sunlight reaching the Moon, hence, we see the phases of the Moon when it is behind the earth with respect to the sun. At this point I would slide two circles of card, a white and a black one (with the black one bigger than the white one) past each other (black on top). If the black card is the shadow cast on the Moon by the earth (essentially what happens in a lunar eclipse), the shapes of the Moon due to the light reflected back to earth are considerably different than the shapes we observe from the phases of the Moon. So, we have establish that this model is a misconception.

Now we can introduce a better model and I use the pingpong ball in the image below with the students in the centre of the room. They are the observers on the earth and the light from the sun is coming from the left hand side in the photo.

If you go around the learner in the middle of the class making sure the “lit” face of the pingpong moon is always facing the wall on the left in this case, your students will see the same shapes we observe during the phases of the moon.

To reinforce this demonstration you could show the students this great animation by Keith Gibbs (also available in HTML5 if using an iPad).

Ok, now for the icing on the cake that you’ve all been waiting for! Check out the video below that shows a cresent moon through an infrared camera. You can see the crescent really bright, but you also see the other parts of the side of the moon facing the earth. I believe that is what is emitted by the moon in the infrared spectrum and that gets picked up by the IR camera. It is really awesome.

When @CardiffScience posted (on Google+) a video demonstration of an arrow drawn on a piece of paper that flipped direction when seen through a glass of water I knew I had to try it myself and write this post. The video below shows the demonstration which is pretty neat, but carry on readying below the video for what I think is the explanation.

As some of you might know, I am one of the Editors of Talkphysics.org with David Cotton and he posted the below photo on this thread, which is think is a convincing explanation of what goes on in my video of the flipping arrow. glycerol_zpsee0be2d7 If you trace the path of the three rays in the Dave’s¬†photo you can see the ray that start from the top slit from the ray box ends up at the bottom on the multimeter. This is essentially what is happening in the video, so the light reflected by the right side of the arrow gets refracted by the water inside the glass and ends up on the left when it reaches the camera. Looking at the photo above though gave me an idea, i.e. “If I go close enough to the glass I should go beyond the focal point of the glass lens and see the arrow flipping again!” – WRONG! That didn’t actually happen. However, I just noticed that Dave’s liquid was Glycerine (at least if the name of his image file tells the truth), so I wondered whether the refractive index of glycerol was such to cause less bending inside the glass, but I was wrong again. In fact, water has a refractive index of 1.33 and glycerol of about 1.47, so there should be more bending of light inside the glass. I¬†still haven’t figured out why I can’t flip the image again if I go close enough to the glass, but I still think it was worth posting this article and if you know the answer, please leave a comment! Thanks!

I have always found it is quite hard to show the path of the current in a bridge rectifier to A-level students using diodes alone. The diodes are tiny, for a start, and you end up following the wire with your finger around, but students seem to get lost in the process. I still introduce the rectifier using diodes and one thing I show them is that even using a DC voltmeter doesn’t change the sign. This is convincing for some, but it is still nice to be able to give further proof of what’s going on.

The diagram might also help, because it is easier to follow the path around.

Bridge Rectifier

However, I have started building rectifiers with LEDs alongside the diode version and it works a treat. The first thing I show them is the circuit on DC current. Only two of the four LED light up, so I can ask “What would happen, if I reverse the polarity?” They now seem to get it and they often answer correctly that the other two LED will light up. I change the polarity several times to simulate the two half-waves, as in the images below.

Then, I get the spinning wheel we use to observe ripples in the ripple tank (the one with gaps, I can’t remember the name) and put the LED rectifier on AC. The result can be seen in the video below.

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.

This is my second mind map in an attempt to visually display the draft Science Curriculum in England and this time the focus of the Mind Map is Energy. In my previous post on this issue I set out to see how coherently the new curriculum has been written and I suggested that depending on how difficult it would be to mind map the various parts of the curriculum could give an indication of that. I have to say that in this second Mind Map I could find quite a few key ideas that interrelated to other branches quite nicely. However, I felt that I had to separate Conservation of Energy from Dissipation of Energy, even though the new curriculum has them under the same heading (which is fine in the document I think), as I wanted to stress the importance of the Principle of Conservation of Energy. Something I was not too sure about was the inclusion of renewable energy sources and fuel resources under the Conservation and Dissipation section. As a whole I am fairly pleased with this Mind Map and I think the development of this unit is quite coherent. I might have missed something though and I value your comments in that respect.

You can use the Mind Map below, or download the iMindMap version and edit it from this Biggerplate page.

Physics Energy

In a previous post I wrote about the Fish Tank Cloud Chamber workshop funded by IoP and organized by Cerian Angharad in Cardiff and I promised I would run one in Gloucester. Well, this evening I did and all delegates had great fun taking part in the filming of the iMovie trailer you can see below. I made using an iPad third generation and it was very easy to do, because these trailers come with the storyboard already set up for you. In fact, all the clips, places for captions and duration of the trailer are fixed, which means that you really need to focus on the message you want to convey and do it in the simplest way possible. But it also prevents you from adding too much to your video. Also, I like the fact that there is no dialogue and the message is communicated entirely through the clips and captions you create!

These are important skills for any learner and I would encourage any educator with an iPad, iPhone, or iPod Touch to let their pupils create these short trailers for their learning. I got the inspiration for this one and other trailers I made by the inspiring work Gavin Smart does with his learners at Priory Community School.