• Created by Unknown User (goodhew_1@touchstonenetwork.net), last modified on Jul 05, 2011 08:38

Concept Questions submitted during the conference (and subsequently by July 4th)
Comments
Some of these questions might be considered to be "brainteasers" rather than true concept questions. However all of them require thought and for the moment none have been excluded. In the first 80 questions there were only two which were submitted twice!
Many of the questions need answers because I am not sure that I can do them correctly! (I certainly did not know the answer to Q69)..
There is at this stage a strong preponderance of questions relating to probability, logic, and to simple physical concepts such as mass, density, force and g.
Peter Goodhew (23rd June 2011)

  1. Draw the free body diagram for a coin just after it has been tossed. [Alternatively: What is the force on a coin just after it has been tossed?] Are the forces on the coin greater on the way up or the way down? Ignore air friction.


A: A single force vertically downward

  1. H2O is heated in a frictionless piston-and cylinder arrangement, where the piston mass and the atmospheric pressure above it are constant. The pressure of the H2O will: (a) increase (b) remain constant (c) decrease (d) need more information.


A: Remain constant (does the question need to specify the phase of the H2O as gaseous?)

  1. About a teaspoon of water-saturated salt sits on the bottom of a beaker. If the solution is allowed to sit for 24 hours and have some of the water evaporate, which curve represents the change in concentration of the salt in the solution from time t1 to t2? (Circle a or b or c) PLEASE EXPLAIN. [Diagrams in concept questions rarely need to be more sophisticated than this.]


A: b, concentration stays constant (assuming solution is saturated)

  1. A large truck collides head-on with a small car. During the collision:
  2. The truck exerts a greater amount of force on the car than the car exerts on the truck;
  3. The car exerts a greater amount of force on the truck than the truck exerts on the car;
  4. Neither exerts a force on the other, the car gets smashed simply because it gets in the way of the truck;
  5. The truck exerts a force on the car but the car does not exert a force on the truck;
  6. The truck exerts the same amount of force on the car as the car exerts on the truck.


A: Same forces, (e)

  1. A system consisting of a quantity of ideal gas is in equilibrium state "A". It is slowly heated and as it expands its pressure varies. It ends up in equilibrium state "B". Now suppose that the same quantity of ideal gas again starts in state "A" but undergoes a different thermodynamic process (i.e. follows a different path on a P-V diagram) only to end up again in the same state "B" as before. Consider the net work done by the system and the net heat absorbed by the system during these two different processes. Which of these statements is true?
  2. The work done may be different in the two processes but the heat absorbed must be the same;
  3. The work done must be the same in the two processes, but the heat absorbed may be different;
  4. The work done may be different in the two processes, and the heat absorbed may be different in the two processes;
  5. Both the work done and the heat absorbed must be the same in the two processes, but are not equal to zero;
  6. Both the work done and the heat absorbed by the system must be equal to zero in both processes.

[Each of the five answers was selected by some students.]
A: I'm not sure about this one. Is it (a)?

  1. If atomic bonding in metal A is weaker than metal B, then metal A has:

a) lower melting point
b) lower brittleness
c) lower electrical conductivity
d) lower thermal expansion coefficient
e) lower density
A: Several of these might be true, but only a) is necessarily true. Perhaps the question should say "metal A must have:"

  1. If you unwrap a new piece of modeling clay that is a rectangular solid 4cm x 4cm x 16cm, which one of the following would most increase its surface area?

a) Press down on a long side (making it, e.g. about 16 x 8 x 2 cm3)
b) Form it into a cube, about 6.5 cm per side.
c) Form it into a cylinder, keeping the length about 16cm.
d) Make a sphere.
A: Must be (a) because 8+2 > 4+4

  1. What do these three processes have in common?

Rust forming on iron nail
Water evaporating from a dish
A piece of candy dissolving in your mouth
a) The rate of change depends on the mass of the substance.
b) All three processes involve a change in phase.
c) All three processes are chemical reactions.
d) All three processes occur at the surface of the substance.
e) All three processes depend on the solubility of the substance. [Light et al]
A: All are surface phenomena (d)

  1. You are in an elevator travelling upwards at constant velocity. Suddenly you drop your keys: It so happens that when they strike the floor they are at the same height above ground level as when they left your hand. The keys fall dead on the floor without bouncing. Make a single graph showing qualitatively the height above ground of both the keys and the elevator as a function of time, starting before the keys are released until after they strike the floor.


A: Straight line with slope v, parabola rising and falling to the start height, straight line of slope v.

  1. Suggest 3 hypotheses to explain the observation that a bar of soap appears to give less lather as it gets smaller.


A: a) smaller bar has smaller surface area;
b) lanolin was not deposited uniformly throughout the bar (e.g. the centre is lanolin-deficient), and
c) lanolin leaches out of the bar as it is used (diffusing to the surface and leaving a lanolin poor core)
.

  1. You are sitting in your kitchen on a hot summer day. In order to cool yourself down you open the door of the fridge. Is this a good idea? What happens to the temperature in the room after, say, one hour?


A: In a closed system (the room) as the fridge continues running the heat generated by the cooler will more than balance the heat extracted from the air, so after the initial waft of "cold" shortly after you open the door, the room will get warmer.

  1. You throw a ball at your friend, making it bounce once before she catches it. Draw the force on the ball at five locations, including the moment it bounces. Use an arrow whose direction shows the direction of the force and whose length gives an indication of the magnitude of the force.


A: Four equal force arrows downwards, one (at the point of bounce) larger and upwards

  1. You are in a small boat in a small pond. You have a six-pack of beer with you. You throw it into the water and it sinks (what a shame!). Does the water level in the pond rise, fall or stay constant?


A: In the water it displaces its volume. In the boat it displaces its mass of water (which must be higher because it sinks!) Therefore the water level falls.

  1. What is the chance that the next person you see will have more than the average number of arms?


A: Unity because there are some people with 1 or zero arms but none with 3 (apart from Zaphod Beeblebrox) so the average (mean) number of arms must be less than 2.

  1. What is the chance that the next person you see will have more than the median number of arms?


A: Zero – the median number is 2

  1. You want a cup of white coffee but have little time before you must leave. The coffee is very hot and the milk is cool. To maximise the chance that your coffee is cool enough to drink before you have to leave, should you add the milk immediately or just before you drink it?


A: Add the milk as late as possible: Newton's Law of Cooling indicates that the rate of cooling is proportional to the temperature, so hotter liquid (black coffee) will cool faster.

  1. You fire a bullet parallel to the ground and drop one at the same time. Which hits the ground first?


A: They hit the ground at the same time (ignoring second or third order effects such as the non-spherical shape of the earth).

  1. A truck-load of chickens is on a weigh-bridge. They suddenly all take flight. Does the indicated weight of the truck change?


A: If the truck is closed the state of the chickens makes no difference (their wings have to exert the same pressure as their stationary weight would have done). If the truck is open then the air pressure could reduce and the truck would appear lighter.

  1. You suspend a book by a thin string. To the bottom of the book you attach a similar thin string. You jerk the lower string – which string breaks first? In a second experiment you pull slowly on the lower string – does the same string break?


A: If you jerk the string the lower string breaks, because the string will break before you can accelerate the inertial mass of the book. If you pull slowly the upper string will break first because it will be carrying the additional load of the book and will experience a higher stress than the lower string.

  1. The ice cube in your drink melts. Does the level of your drink rise, fall or remain steady?


A: Remains the same. In both cases the same mass of water is being displaced.

  1. A river runs past your house. One year a hydro-electric power station is built a kilometre upstream from you. What difference would you be able to detect in the water flowing past your house?


A: It must be cooler, because energy is being removed upstream but the volume and flow rate remain the same.

  1. A ladder is upright against a vertical wall. Both the wall and the floor are perfectly slippery (no friction between ladder and floor or wall). You pull the bottom of the ladder away from the wall slightly and it starts to slip down. At some angle it loses contact with the wall. What does this angle depend on?


A: Dimensional analysis shows that the angle (with no dimensions) must be independent of mass, g or length (as long as g is non-zero, so that there is a downward force acting on the ladder)

  1. During cooling from high temperature, small spheres solidify homogeneously in a metallic melt which consists of A and B atoms. The composition Cx in the centre of the spherical nuclei below is richer in atom B compared to the surface. Which of the phase diagrams below is appropriate for this alloy?














A: The second (blue) diagram

  1. Why can a wind turbine never extract all the energy from the wind?


A: Because if all the energy were removed from the wind, it would then be stationary and could not turn the turbine.

  1. Three materials are tested in tension, giving the stress-strain curves


25a. Which material is most ductile? (C, with greatest extension)
25b. Which material is the toughest? (B, with greatest energy dissipation = area under curve)

  1. Topic: Power considerations in amplifiers

Degree: electronic engineering, but basic enough to be used in any elementary electronics course of any engineering
Justification: Students usually pay attention to the characteristics about signal processing in amplifiers (bandwidth, gain, …) but often forget the limits set by power supply
Question: An amplifier provides a sinusoidal output voltage to a 8 Ω load (e.g. a loudspeaker). If it is powered by a unipolar power supply of 5 V, which is the maximum power that can be transferred to the load?
Answer: The maximum voltage excursion at the amplifier output is 5 V peak to peak (considering an ideal amplifier without dropout). Then the rms output voltage is 2.5/sqrt(2)=1.77V and the power over the load is 1,77^2/8=390 mWrms
Advanced answer: If a switched structure (Class D) using a H-bridge is employed, the maximum voltage excursion at the amplifier output is 10 V peak to peak (5V) and the output power is then 1,56 mWrms
Alternative question: if we double the supply voltage of an amplifier (i.e. from 5V to 10 V), the maximum output power delivered to a resistive load:
a) remains the same
b) is doubled
c) is 4 times higher (correct answer)
d) is sqrt(2) times higher

  1. Applicable to aerodynamics, flight mechanics, Consider a bicyclist riding a flat road, with no wind. The rider's fuel burn rate (cal/HR) is reasonably assumed proportional to power required, and air drag is the sole resisting force. Is the fuel burned over a fixed distance:1- invariant with velocity?2- proportional to velocity?3- proportional to velocity squared?4- proportional to velocity cubed?Correct answer is 3.The drag is proportional to V^2.  The power required i/ drag times velocity, and hence proportional to V^3. So burn per unit time is proportional to V^3. The fuel burned per distance is the burn rate divided by velocity. Hence the fuel consumption over a fixed distance is proportional to V^2, and directly proportional to the drag.


  1. (used as example by Mazur) Metals expand when heated. If a sheet of metal containing a circular hole is heated will the diameter of the hole increase, decrease or remain the same?


A: Hole diameter increases. Imagine that there was metal in the hole, then it would expand. Alternatively imagine the perimeter of the hole; the metal here expands and therefore the hole gets bigger.

  1. (Jim McNeely question – needs diagrams) x and y sensors are 90 degrees apart giving Vout proportional to distance from shaft. Shaft is bent slightly, and rotating. Output voltages are shown below (diagram: sine curves). In what direction is the shaft rotating? Clockwise viewed from R, clockwise viewed from L, or can't tell.


A: I need an answer to this!

  1. If a black box is connected by a wire to a weight in a gravity field, and the weight is observed to rise, the energy in the black box rises, falls, stays the same, can't tell?


A: Energy is transferred to the weight so the energy in the black box must decrease.

  1. If a vertical load is applied to a beam with the cross-section shown (T shaped), the tip of the beam will deflect down, down and left, down and right, can't tell?






A: I don't know

  1. If a plate made of anisotropic material is deflected by a load at the tip (diagram), then deflection at A = deflection at B,

Deflection at a > deflection at B
Deflection at A < deflection at B?
A

B




(note: I do not understand what is meant by "anisotropic" in this context. Most materials are anisotropic in some way, with Poisson ratio not exactly 0.5)

  1. When given the requirements for a new system, as the designer you should: take them as given; question the supplier and perhaps redefine them; ignore them and make a great product?


A: This is ambiguous. Who is the supplier? Does this mean the supplier of the requirement or the supplier of the product or system (both words used in the question)? Intended A is probably Question the supplier and negotiate.

  1. Define the distributed vorticity in this flow (diagram, V proportional to 1/r)











A: I have no idea what this is about!

  1. How much power is required to maintain the speed of a bicycle on level ground at 30km/hr?


A: In the absence of wind resistance or rolling resistance, zero

  1. What is the principle (or did he mean principal?) difference between the two bridges shown? (diagram)










A: I have no idea

  1. to 46




















  1. You are driving a motorbike on a highway. Explain what will happen if you gently turn handlebar to right (or to left). Try to figure out how the bike turns.


A: ???

  1. Chemical Engineering CQ: You are an engineer who is to design an insulation system for a reactor and you have two types of insulating materials. They have heat transfer coefficients where K1 > K2. How will you arrange the layers to obtain a better insulation and why?


A: ? (are the available materials of similar thickness or doesn't it matter?)

  1. Chemical Engineering CQ: What is the basis of selecting the shell side and tube side fluids of a shell and tube heat exchanger?


A: ??

  1. What does it mean to say that an equation is linear?

A: I'm not sure. Does it have at least one variable not raised to any power?

  1. What does it mean to say that a system of linear equations has no solution?


A: ??

  1. Why can't a material be (completely) stiff?


A: because if you hit a piece of such a material, a wave would travel through it faster than the speed of light in vacuum, which would clearly violate the laws of physics, as we know them
 
Comment: Should the wording be more helpful? We do not usually refer to complete stiffness. Also the reasoning required is quite sophisticated, especially if there is no mention of intermediate ideas such as the interatomic potential.

  1. Two twins jump off a springboard next to each other. Will they fall faster if they hold each other's hands (turning them into one body with twice the mass)?


A: Of course not, which demonstrates that all objects accelerate at the same rate (air resistance neglected)
 

  1. A ship passes slowly across an aqueduct between two dams. How does the load on the aqueduct change during this process? (The passage is so slow that there aren't any waves.)


A: it doesn't change at all since it is only a function of the water level, which is obviously constant

  1. A current flows in the overhead power line of an electrical railway (or tram). Where does it go after that?


A. A closed circuit is necessary in order to get a current. The current continues through the locomotive engine and returns to the power station via the wheels and the rails
 

  1. Why do small animals have to eat so much more relative to their weight than large animals have to eat?


A: in order to maintain their temperature. Small animals have a larger proportion of their cells close to the surface, which is the same thing as saying that they have a larger relative surface. If L is a characteristic length of the body, the surface area A is proportional to L2 while the volume V is proportional to L3. A/V = 1/L, which becomes larger the smaller L is
 

  1. Is it worth it to bend down and pick up a penny from the street?


A: (example of a Fermi problem). Compare the price of the energy needed to lift your body again after having kneeled down with the value of the coin
 

  1.  While you are driving you have a helium filled balloon in the middle of your car. If you accelerate, which way does the balloon go relative to the car? Backwards, forward or does it stay where it is?


A: it goes forward. (A positive) acceleration is like if the car was hanging with the front pointing up, which makes the air thicker and forces the balloon to float "upwards".
 

  1. How does the force on a bicycle wheel propagate from the road through the tyre and up through the rim and the spokes to the hub?


A: don't know, but a free body diagram ought to answer the question
 

  1. Does a bathtub vortex rotate in different directions in the northern and southern hemispheres?


A: no, it can go either way in both hemispheres. There IS an effect that works in different directions, but that is extremely weak compared to other effects  and cannot be observed in a bathtub. There the rotation is due to VORTEX STRETCHING, and the vortex can easily be stopped and started in the opposite direction by hand.
 

  1. Why does a longer train generally travel slower than a shorter train with the same mass and traction power?


A: the maximum speed is determined by curves and gradients along the line, and in a long train a part of it is more often at a slow section, keeping the speed of the whole train down
 

  1. Why is there a maximum height that a tree can reach?


A: The mechanical stress is determined by the ratio mass/cross section area, which increases with the height (if it keeps its proportions)
 

  1. Draw a free body diagram of the International Space Station (ISS) in its orbit around the earth


A: the station is in free fall and the only force on it is directed towards the centre of the earth
 

  1. A cylinder of water in a body of water has weight = height X pressure at area of bottom (W = ρAgh). A cone of water with the same bottom area and height should surely therefore weigh the same? Why not? [diagram needed]










A: There are forces perpendicular to the "vertical" walls. In the case of the cylinder these cancel exactly. For the tapered shape there is a non-zero resultant in the vertical direction which cancels part of the bottom force.

  1. Is it true that you are most likely to be in the busiest lane of a motorway? If so, why? If not, why not?


A: Yes, by definition the busiest lane contains more cars, so your chance of being in this lane is higher than for the others

  1. Fair share

Two identical beakers, one half‐full of whiskey, one half‐full of water. Scoop out some whiskey out of beaker 1, and pour it into the water beaker (2). Than scoop the same volume of mixture out of beaker 2, and pour it back into beaker 1. Do you have more (less, or same) amount of whiskey in the water than you have water in the whiskey. (Works equally well with rum.)
Comment: John Dalton did something similar to compare atomic weight
A:

  1. You have ten bags of identical coins, plus a very good scale. The Leprechauns have switched a bag of yours with a bag of theirs: their coins being slightly different in weight. Can you, with a single weighing, determine which bag is the Leprechaun's?


A: I can't!

  1. Are all girls equal (equal to … ? Just 'equal')

"Far too many boys and not enough girls in this country! How to reduce the births of boys and foster that of women so as to bring the proportions back into balance?"
"Easy: Set the law so that families can procreate at will as long as 'It's a girl!', and have to stop the first time that 'It's a boy!' You'll have families with only one boy, some with one boy and one girl, ... , some with one boy and four girls, etc. But never a family with more than one boy. So you're bound, overall, to have more girls than boys that way."
Right or wrong? Why?
A: Wrong. Half of the families will have a boy first and thus will be "all boy" families. All other families will have one boy and one or more girls. There will be a substantial preponderance of boys!

  1. Can trains turn at all?

"Daddyyy!
Yessssss?
How can the trains turn?
Well they just follow the track, dearest little one.
But daddyyy!! On a train, both wheels are linked together with a stiff rod of steel. In a turn, the outer arc is bound to be longer than the inner arc. One of the two wheels should skid or the rod should twist. I saw a train turn the other day, and none of the two happened: no skid and no twist … So Daddyyy,how
come the trains can turn?
…What school do you go to?…"
How can the trains turn, no skid, no twist?
A: Their wheels are conical, not flat, and move to change the effective radius

  1. Row, row, row your boat

You paddle away in your canoe, with a half‐bottle of champagne tied to the boat and floating in the river to be nice and cool. Oh rats! The knot isn't well made, and the bottle floats away in the current. You realize this is so only 60 min later. You turn around, and paddle towards the bottle, applying the same force on the paddle as you always do. (Very constant individual.)
Will it take you more time, less time, or the same amount of time to paddle towards the bottle with the current, than the time you paddled away from the bottle against the current?
A:

  1. You and Zeus

Zeus will let you down the mountain only if you can guess which of three apparently identical spheres, all of equal mass, is hollow and empty. You know one is solid homogeneous material, one is hollow and filled with liquid, and one is hollow and empty. You cannot touch, knock, handle the spheres, only Zeus can approach them.
What can you ask Zeus to do with the spheres, to help you guess which is hollow and empty?
How will you determine which is hollow and empty?
A: ? Spin them, suddenly stop them then release them. The ball filled with liquid will start rotating again. Eliminate this one. If Zeus could measure the force needed to stop them spinning you could probably deduce which was hollow from its higher second moment?

  1. You can fly!

Windy, and not windy. Model planes are flown from post A to B, and back. Constant wind – if some – from B to A. Will the planes take more, less, or the same time to do the round trip with or without wind?
A:

  1. ...But can you float?

A boat filled with iron scrap is in the locks. Doors of the locks are closed tight (sealed), and pumps inactive. For some reason the (infamous) captain decides to dump all the iron scrap in the locks. Will the level of water go up, down, or stay the same with respect to the walls of the locks? [this is the same as the earlier question 13 about the six-pack, so the level falls]

  1. Red chair

On the ski slope, there is a little flat ¾ of the way up, where you like to stop for the sight. Alongside is the chair lift, with all blue chairs but one, which is red. Playful expectation, you stop on your little flat until the red chair comes by. But, but... Your statistics show you see the red chair going up much more often than it goes down. How can this be?
A: ??

  1. Windows

Two friends haven't seen one another for a long, very long, time.
 I have three kids now, you know.
No kidding. How old are they?
 Well the product of their age is 36. The sum of their age is... is... Ah! Is equal to the number of
windows in the wall over there.
(Work, think, compute,...)
This cannot be solved!
 What? Let me see... Oh! You are right. It cannot. Well the last one has blue eyes.
Why did you not say so in the first place. If the last one has blue eyes, then their ages have to be...
How old are the kids, and how could he find out?

  1. Ferry

A ferry boat runs along a cable because the cross current is too strong. The motor breaks down. What can you do to go on ferrying along without a motor, and not touching or pulling on the cable?
A: ??

  1. So hot

So hot a day. Quick! Shut the windows and open the freezer. That should cool the room down. [same as question 11] True or false, and why?

  1. Three switches individually connected to three matching floodlight projectors hundreds of meters away. You want to know what switches what, but cannot see the lights unless you walk to them. How can you do it in one and only one trip to the floodlights?


A: Switch one on. Switch the second on for a minute and then off. Leave the third off. Walk to the lights – one will be on, one will be warm and the third will be cold!

  1. If you want the best mixing, should you then pour the (smaller) quantity of milk/cream into the (larger) quantity of coffee/tea, or vice versa? And why?


A: pour the larger quantity into the smaller. It will have a larger total kinetic energy, which by viscous dissipation results in a better mixing before the combined body of fluid comes to a rest.

  1. How much water (litres) is needed to keep a large ship afloat?


A: Only as much as is needed to separate the ship's hull from the surroundings, which means that if the ship is in a dock with the same shape as the hull - only slightly wider - a few litres would be sufficient.

  1. What is the highest temperature you can get in a solar collector?


A: About 6000 degrees Celsius, i.e. the temperature on the sun's surface. (You would otherwise violate the 2nd law of thermodynamics and have invented a perpetuum mobile in that you could transfer heat back and forth.)

  1. You are given a rod of soft material. When you pull it, it gets thicker. What is the value of its Poisson ratio?


Greater than 0.5
Between 0.25 and 0.5
Between zero and 0.25
Zero
Between 0 and -0.5
A: Negative

  1. You have two identical flat bars of steel. One is a permanent magnet, the other is unmagnetised. How do you determine which is which, without any other equipment or materials?


A: bring the end of one bar (A) up to the middle of the second (B). If A is the permanent magnet it will attach quickly to B (click!). If A is not the magnet you will feel nothing as it approaches the centre of B, where B's N & S poles exactly cancel.

  1. Describe how to reverse the order of single-link, linked list.


A: ??

  1. I am standing in a boat that is floating on still water in canal with no wind and holding two identical fire hoses. Both hoses are supplied from the same pump, which gets its water supply from the canal upwards through the flat bottom of the boat. One jet of water is directed against a concrete wall. The other has an identical mass flow rate and velocity in the opposite direction. Does the boat


(a) move away from the wall
(b) not move
(c) move towards the wall
(d) I need more information 
A: (b) It doesn't move. There are no unbalanced forces on the boat in the horizontal direction. A momentum balance shows equal and opposite momentum changes in the water which balance each other. The jet exerts a force on the wall. The other jet also exerts a force on the water in the canal, but neither of those forces acts on the boat. The same principle is in play when a rocket produces thrust in a vacuum, even with nothing for the exhaust to "push on".

  1. A fly is flying from north to south when he crashes into the windscreen of a train that is travelling at high speed in the opposite direction. The fly is splatted on the windscreen of the train. During this process the fly changes direction from flying southwards to travelling northwards so he must have stopped and changed direction at some point. He presumably did this whilst in contact with the windscreen of the train. So he must have been going the same speed of the train. So the train must have stopped? Where's the flaw in this argument?


A: ??

  1. A lift (elevator) has a "car" in which people ride up and down to get from floor to floor. There is a counterweight that balances out the weight of the car. An electric motor is required to power the lift (for starting and stopping.) The lift company is asked to provide a design for a lift to be used on the moon instead of the Earth. Acceleration due to gravity on the moon is about a sixth of that on Earth. The lift should have a similar characteristics in terms of the speed of the journey of the passengers. What needs to change. Select the correct answers:

(a) The counterweight should be about the same mass
(b) The counterweight should have a much greater mass
(c) The counterweight should have a much smaller mass
(d) The motor should have about the same power
(e) The motor should be much more powerful
(f) The motor should be much less powerful
A: I think the answers are (a) and (d). Assuming the car is about the same mass (it might be slightly more flimsy but not a lot) then the counterweight would be the same. The motor is mainly used for acceleration and deceleration of the car, counterweight and passengers – the mass of these is unchanged.



Roll of Honour (with apologies to those who submitted their questions via another person!)
Göran Gustafsson
Guy Cloutier
Ed Crawley
Jim McNeeley
Andrew McLaren
Gillian Saunders
Ramon Bragos
Mia Knutson Wedel
Rob Niewohner
Lauri Miika Kantola
Chua Poh Hui
Eduarda Pinto Ferreira
Matt Murphy
Anonymous
Rick Sellens
John Fothergill

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