Great demo for conversion of energy. Definitely quite fun to setup and fire. Use tennis balls as ammo, but ideally something heavier should be swung on this although safety concerns would kick in. I think water bombs make a good ammo too.
Friday, February 4, 2011
Physics : Trebuchet
Built this trebuchet in 2009 in preparation of a science camp. Didn't get to use it, but still hope to do so in a camp sometime soon. Test fired it; needs refinements on the release mechanism.
Great demo for conversion of energy. Definitely quite fun to setup and fire. Use tennis balls as ammo, but ideally something heavier should be swung on this although safety concerns would kick in. I think water bombs make a good ammo too.
Great demo for conversion of energy. Definitely quite fun to setup and fire. Use tennis balls as ammo, but ideally something heavier should be swung on this although safety concerns would kick in. I think water bombs make a good ammo too.
Physics : Chladni Patterns
Chladni patterns are a really cool way to visualize standing waves.
For more info on the man and the field he helped pioneer:
Ernst Chladni on Wikipedia
Cymatics on Wikipedia
I rigged a speaker to an amplifier and a frequency generator. The speaker was modified such that the cone directly drives a square metal plate. Yellow art sand was added and when certain frequencies were dialed into the frequency generator, the sand would quickly coalesce to form patterns.
More details on setup will be posted here. I'm still working on it at the moment.
Meanwhile, enjoy the pictures!
For more info on the man and the field he helped pioneer:
Ernst Chladni on Wikipedia
Cymatics on Wikipedia
I rigged a speaker to an amplifier and a frequency generator. The speaker was modified such that the cone directly drives a square metal plate. Yellow art sand was added and when certain frequencies were dialed into the frequency generator, the sand would quickly coalesce to form patterns.
More details on setup will be posted here. I'm still working on it at the moment.
Meanwhile, enjoy the pictures!
Thursday, February 3, 2011
GP Essay : Music has one purpose – to entertain
I wrote this GP essay some time ago for one of my students.
Makes for an interesting read; not the regular current affair GP essay question.
Click here for the essay:
Chem : Table of the Solubility of Ionic salts
Solubility List
Exceptions
All Sodium Salts are soluble
All Potassium Salts are soluble
All Amonnium are soluble
All Nitrates are soluble
These exceptions over-ride the solubility table below. A useful way of remembering this is to recall the word SPAN.
Solubility Table
| Soluble | Insoluble | |
| Sulphates | All soluble except | Barium, Lead, Calcium, Silver, Mercury |
| Hydroxides | Barium and calcium slightly soluble | All other hydroxides insoluble |
| Carbonates | All insoluble | |
| Chlorides | All soluble except | Silver, Lead, Mercury |
Chem : Metal Reactivity list
'O' level Chem Metal Reactivity list with Hydrogen and Carbon.
| Metal Reactivity list | ||
| Common Name | Symbol | Illustrative examples |
| Potassium | ||
| Sodium | ||
| Calcium | ||
| Magnesium | Burning Mg underwater | |
| Aluminum | Aluminum Pots. Thermite. Napoleon III VIP Dinnerware | |
| Carbon | The Blast Furnace | |
| Zinc | Galvanized Roofing | |
| Iron | ||
| Tin | The tin can | |
| Lead | Plumbum | |
| Hydrogen | ||
| Copper | ||
| Silver | Tarnish | |
| Gold | Aqua Regis |
Chem : Cation and Anion List
This is a list of cations and anions commonly encountered in 'O' Level Chemistry.
Common Cations
| Name | Formula |
| Aluminum | Al+3 |
| Ammonium | NH4+ |
| Barium | Ba+2 |
| Calcium | Ca+2 |
| Copper(I) | Cu+ |
| Copper(II) | Cu+2 |
| Iron(II) | Fe+2 |
| Iron(III) | Fe+3 |
| Hydrogen | H+ |
| Lead(II) | Pb+2 |
| Magnesium | Mg+2 |
| Potassium | K+ |
| Silver | Ag+ |
| Sodium | Na+ |
| Zinc | Zn+2 |
Common Anions
| Simple ions: | |
| Fluoride | F- |
| Chloride | Cl- |
| Bromide | Br- |
| Iodide | I- |
| Oxide | O2- |
| Sulfide | S2- |
| Hydroxide | OH- |
| Phosphate | PO43- |
| Sulfate | SO42- |
| Nitrate | NO3- |
| Carbonate | CO32- |
| Dichromate | Cr2O72- |
| Permanganate | MnO4- |
Q : Why the name Cations?
A : These ions are Positive in charge, and gather at the Cathode during electrolysis.
Q : Why the name Anions?
A : These ions are Negative in charge, and gather at the Anode during electrolysis.
Wednesday, July 8, 2009
Physics : Diffraction through a privacy filter
I was wandering through the scraps and parts shop one day in the merry month of May and saw a stack of what appear to be privacy filters torn off old ATM machines. Knowing that they contain a mesh of fine fabric, I gambled that they would serve as a grating. I bought them for a song; they were 80 cents a piece because the owner didn't know what they were.
A trip home and a flash of the laser pointer later, the filters showed a promising diffraction pattern right off the bat. I set up the expriment in the manner shown below:
The first task at hand is to estimate the pitch of the grating.
A trip home and a flash of the laser pointer later, the filters showed a promising diffraction pattern right off the bat. I set up the expriment in the manner shown below:
The first task at hand is to estimate the pitch of the grating.
At a distance of 50cm between grating and screen, I measured the distance between the zeroth and 7th maxima to be 2.05 cm. Using the formula nλ= dsinθ, with tanθ=2.05/50, and nλ=7X650nm, d works out to be 0.111 millimeters, which seems reasonable considering the grating is made of fabric fibers of some sort or other.
I also obtained an enveloped diffraction pattern with a red and green laser. Granted the lasers have different spot sizes and frequencies, they both show how the diffraction pattern on the screen is subjected to an envelope when multiple aperatures are involved. Estimating a beam spot size of approximately 1mm, we would expect the laser to pass through about 9 aperatures.
The diffraction pattern obtained with a red 650nm laser.
The diffraction pattern obtained with a green 532nm laser.
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