Space Hopper
There's a cracking game at:
http://www.miniclip.com/games/space-hopper/en/
You have a little spaceman and you have to collect stars. After the first level there are different density planets which you can tell from the height you can jump - and it's fun!
Magdeburg hemisphere for less than a tenner!
I found these dent pullers at Rapid:
http://www.rapidonline.com/searchresults.aspx?style=0&kw=dent+puller
The 110cm ones are £1.95 each and two make great Magdeburg hemispheres. With p & p under a fiver, that's still less than a tenner!
Bill Haley and the Comets
You can download a snippett of the original "Rock around the Clock" song from:
http://www.physiol.ucl.ac.uk/ashmore/
..oh and there's some video or other that's with it.
A free signal generator
I found this nifty bit of freeware at:
http://www.dr-jordan-design.de/signalgen.htm
Does up to 20kHz and has different wave shapes and fine and coarse control.
Putting the Phyzz into Physics
I want to try to communicate my excitement about physics to the girls I teach.
I have decided to try and add something each week that makes them think outside the current curriculum - maybe a 'wow' moment, maybe a 'why does it do that' moment, maybe an image ......
So this week I did the marshmallows (thanks to Neil Gupta for this)
It drew suitable oohs and has - so that by Friday older sisters were asking when they were going to see it as their younger sisters had already seen it.
Th eonly trouble was if I did it at the beginning, the valuable ensuing discussion ran on and we struggled to do the meat of the lesson.
I now have to collect many more so that there is a different one every week for 5 years!
And just at the right time Paul Nugent drew my attention to David Featonby's article.
Next week the colour change ducks I bought in Sainsbury's in the post-Christmas sale.
Special Relativity Poem
During this weekend, I celebrated Burn Night with some old friends. This annual running joke requires each person to write a poem on a topic of their choice. Always looking for an opportunity to bring physics to the masses, I chose to write about:
The Special Theory of Relativity
A learned man, Galileo by name,
Once said that all physics should be the same,
For everyone in an inertial frame,
Moving at constant velocity.
Then a Scott called Maxwell caused a schism,
With his theory: Electromagnetism,
That predicts many things with precision,
But says light's speed's a constant.
So what is the light travelling through?
And if it's a constant, then for who?
It must, it was reasoned, be with reference too,
A medium that they called The Aether.
Quickly they rushed to their chalk and their boards,
A difference if moving away and towards,
The Aether - if measured would reap great rewards,
But Michelson / Morley found nothing.
So a great contradiction in physics remained,
To preconceptions, the experts were chained,
‘Til a mind such as Einstein's, that unconstrained,
Offered a simple solution.
What if light travels the same speed for all?
The Aether's a fiction, a cerebral shawl,
We can't treat light like a stone or a ball,
Velocities don't add and subtract.
And what follows on from this idea sublime?
All the dimensions distort and combine,
Contraction for space; dilation for time,
Energy and mass conflate.
It doesn't stop there, I hope you will see,
That's just the Special Theory of Relativity,
Acceleration and gravity,
Are left for another poem.
By James Sheils
The Physics of Christmas
Here's a book that sounds interesting:
http://www.amazon.co.uk/gp/product/0316366951/ref=sib_rdr_dp
I shall add it to my list for next year.
At the Amazon site you can search through some of the content.
Happy New Year!
A Christmas Cartesian Diver
James and I had fun with this Cartesian Diver with added snow effect.
Here's how to make it:
1] Get a clean empty pop bottle, some glitter, permanent ohp marker pens, a bit of white plastic from an ice cream tub or similar, a bendy straw and a paperclip, some white acrylic paint and a brush.
2] Mark a thick line around the bottom of the bottle, 3-4 cm up, all the way around.
3] Paint the bottom of the bottle on the outside with the white paint up to this line. Trying to paint inside the bottle doesn't seem to work well as the paint doesn't dry.
4] When the paint is dry draw Xmas iconic images, snowmen, reindeers, Christmas tree and most importantly a chimney on the outside of the bottle.
5] On a bit of white plastic small enough to fit through the hole in the bottle draw a Santa.
6] Put the water in the bottle almost to the top.
7] Bend the bendy straw and cut off the excess so that you have two even lengths coming off from the bend.
8] Hold the ends together with the paperclip and also keep the plastic Santa in place with it.
9] In a dish of water get the straw/paperclip/Santa combination to just float by making sure there's just enough trapped air in the bend of the straw to keep everything afloat.
10] Carefully but quickly put the Santa diver in the bottle.
11] Put the top on the bottle and squeeze and make sure the Santa dives. (If he doesn't fish him out and adjust - putting your mouth over the undone top and sucking will sometimes make him float if he's sunk)
12] Finally add the glitter for the snowstorm effect.
(There are more detailed instruction here: http://www.sciencetoymaker.org/diver/assembl.html.)
Squeeze the bottle to get Santa to drop down the chimney!
Quantum Ball
Have you seen these in Hawkins Bazaar?
They call them switch ball
When you throw it up in the air, with a bit of spin, it opens out so it is neither green nor orange, then when you catch it, it decides which to be.
In other words, you can only tell which state it is in when you have stopped it!
[Thanks go to Michael Brimicombe for this one]
Powerball
I got one of these the other day and just wish I could find a good use for them. There's some gyroscope type bits inside (I've resisted cracking it apart just yet) and it spins at 10,000 rpm. But you start it with a length of string and then your hand just keeps it going. When it's going fast enough it lights up but according to the box and leaflet there's not battery inside. So presumably there's a coil and magnet somewhere and at 10,000 rpm you can generate enough electricity to light the LEDs inside. The forces you feel are quite big - it's sold as a strength exerciser and that seems reasonable; it makes my arm ache anyway. Apart from being a great generator what else could it be used for?
The website is here: http://www.powerballs.com/
I don't think my web cam is going to be fast enough to make a decent movie of what's happening! Try the powerballs website.
Reply To The Christmas Tree
Folloing Gary's post with attached worksheets, I was inspired to build a working model of his idea.
After using card, paint, felt pens, scissors, a hack saw, postage tube, croc clips, tape, 10g & 20g masses and about 2 hours this is the result...
Thanks Gary for such a good idea!
Air Track Model For Uncertainty Principle
Motivation
I was teaching fundamental forces as part of AQA AS Physics (Spec A) Module 1. The topic was about exchange particles as an alternative for "action at a distance".
One bright pupils asked, "but why doesn't the proton eventually disappear? It keeps shooting out pions, won't it eventually run out of mass?" Good questions!
The Student Support Material (Collins) gives the following explanation (page 17):
"But where does the energy to create these particles come from? According to Heisenberg's Uncertainty Principle, particles of energy ΔE can be created for a time Δt, provided that the product ΔExΔt does not exceed a certain value know as h, the Plank constant, which is a very small number, 6.626 x 10-34Js. The Uncertainty Principle allows particles to appear for a short time before being annihilated again, provided that ΔExΔt<h."
Now, ignoring the mistake in the inequality, it can be appreciated that a pupil 4 weeks into A-Level study may find this explanation a little confusing.
To encourage curiosity, and the fact that the pupils were clearly not satisfied with leaving this alone, I decided to take a lesson to discuss the Uncertainty Principle and it's implications. I developed a model to get the main idea across.
Set-Up
You will also need balls of increasing size but decreasing mass. For example:
- ball bearing
- ping-pong ball
- small plastic football
- beach ball
Set up the rest of the equipment as follows:
Teacher Notes
The model tries to show the limit of measured values of the position and momentum of a particle. It does this by using balls as photons and throwing them at another ball that represents the particle to be observed
It is concerned with this version of the Uncertainity Principle:
Δx X Δp >= h(bar)/2
I have been unable to come up with a model fo the energy-time version so, for now, this will have to do.
The model corresponds as follows:
- The ball on the runner of the air track models the particle to be observed
- The other balls model photons of light of varying wavelength (and therefore momentum). The big balls have a large wavelength (corresponding to the diameter) and a bigger mass (to model momentum)
- The air track is used to eliminate friction so the paticle can gain momentum and gives the particle a clear difined axis (for a one dimensional case)
- The screen obscures the pupils' view of the particle to highlight that the only way to know what it's doing is to bouce light off it
It also uses p=h/λ for the momentum of a photon.
Throw the photons at the particle and remember to throw them at about the same velocity (the speed of light is constant).
Narative
Start by giving pupils the relationship p=h/λ. Hightlight the inverse relationship and relate this to the different sized balls.
Don't let pupils see how the particle is moving at the start and tell them not to assume that it is stationary. Start with the biggest ball and work down to the smallest. This reinforces the idea that the only way to see a particle is to bounce light off it. Let's start with the beach ball:
As the beach ball has a big wavelength (it is a big ball), we can't quite tell where the particle is. Trace the extreme edges of the ball as it enters in the screen and bounces out off the particle. Demonstrate that the best we can say is that the particle is somewhere within the diameter of the beach ball.
However, we can tell the momentum of the particle quite well. Point out that the particle's momentum has only altered slightly when the photon has been fired at it as we have used a photon with a small momentum (this is why the big balls have small mass). So, we can be pretty sure that the momentum of the particle hasn't changed that much from what it was initially.
This process is to be continued down the smaller balls. For each smaller ball, we have a better idea of where the particle is:
However, we not too sure what it's momentum was due to the photon having large momentum:
Finishing Up
The uncertainty in the particles position is related to the wavelength of the photon (the size of the ball).
The uncertainty of the particles momentum is related to the momentum of the photon (the mass of the ball)
So, we can get:
Δx X Δp = λ X h/λ = h
So, any measurement will be like this or worse:
Δx X Δp => h
Now, the mathematics is clearly rough and suspicious. It's enough to say that the qualitative idea has been explored. What's 4 pi between friends?
Extras
The philosophical implications of this can be explored. Interpretations of QM have been discussed for decades and it is interesting to start a debate about what the Uncertainty Principle says. It seems to be talking about a limit - but of what?
Some possibilities:
- Experimental (limit to what can be obtained from the experiment)
- Epistemological (limit to what we are allowed to know)
- Ontological (limit to what exists)
Archives
Resources
- Institute of Physics
- HyperPhysics
- SchoolPhysics
- PhET Simulations
- Modellus Modelling
- Physics & Ethics Education Project
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