Wednesday, October 01, 2014


Why Can't a Water Pump pump more than about 9 meters?

Q: Even with larger and larger pumps the engineers were confused as to why they couldn't pump deeper than about 9 meters deep, why?

Hint: The pump they used was at the surface and brought up water via suction. Why is that important?

Hint: I they placed the pump at the bottom and pushed the water up, it worked at greater depths.

A vacuum is just the removal of the air that exists everywhere, so now there's a pressure difference between the bottom of the well (the air pressing down on the water) and the top of the tube where the vacuum is.
The pressure (at sea level) is about 76 cm of mercury.  This is how much it could push.  The weight of mercury vs water is about 13.  So 13.5 * 76 cm is a little more than 10 meters.  But you can never get a perfect vacuum and the water at the surface would start to boil, so the best you could do is about 9 meters.

Wednesday, July 02, 2014


Why is so much DNA used for the sense of smell?

Scientists say that a larger chunk of our DNA than is expected is used to encode our sense of smell, why?

Wednesday, May 21, 2014


Why does a police, ambulance siren go up and down?

Q: Tradition?
A: A little, but old sirens were normally bells which sound a lot different.  There's a more scientific answer.

Q: Is it because you can hear it better?
A: Yes, but why.

Q: Because it's loud?
A: No, it could be loud but make a different sound.  Sirens are almost always going up and down in pitch.

A: The issue is with older people, or people with partial hearing loss.
A: Often you lose hearing at certain frequencies first.
A: By varying the frequencies you have a better chance of finding a frequency that even a person with partial hearing loss can hear.

Sunday, June 28, 2009


How does a train stay on the track?

- The pointy part of the wheel is more there as a backup. If it was actually hitting the rail it would make a lot of noise.
- The left and right wheels are connected by a rod, unlike car.
- The wheels are not flat and the rails are also not flat.
- The wheel is larger on the inside than the outside what happens when you meet a curve?
- What happens is the wheel moves to one side and one side the wheel is larger, the other side (since it's connected) gets pushed and shows a smaller wheel.

See this video with Richard Feynman.

Monday, March 31, 2008


Find out a way to get the area of triangle.

Let's look at rectangle. Imagine a triangle somewhere inside, but with two vertexes in the bottom two corners of the rectangle.

How can we find the area of the triangle? It must be smaller than the are of a rectangle since it fit's inside. The area of the rectangle is just the base time the height (b x h).

If we drop a line down what do we see?
We've split the triangle into two triangles, does that help us?
Actually, we've split it into four triangles, what can you see about these triangles?

Look at the two triangles at the right they look like they are the same size.
Yes they are the same size. Look all the lines are the same length.

So what have we learned?
We can split our original triangle into four triangles two of which are identical.
If we add up all the triangles together, what is it's area? It must be the area of the rectangle which we know is b x h.
So if the 4 triangles = b x h. What must be the size of the two triangles we care about?
It must be 1/2 b x h.


Monday, October 03, 2005


Why are ice cubes small?

Water is one of the few substances that when it freezes it becomes larger. If that's true, why is it that when you get your ice cubes from the tray is often smaller than when you filled it?

Basically, if you opened up the freezer only a few hours after putting them in you should see that the cubes are bigger than when you filled them. But over time, they start to shrink because of sublimation (from ice directly to vapor).

Friday, September 30, 2005


Ess curve on drains

I you look under your kitchen sink you'll notice that the pipe makes a ess shaped curve. Why is that done?

Basically the idea is to trap some water in the bottom part of the ess so that there is a water seal. This way the smells from the sewer doesn't rise up to the house. Also bugs will be less attracted to you sink because it won't be able to smell your cooking, say.

Ceiling fans can heat the room too?

It's possible to use a ceiling fan to both cool off a room and heat up a room.


A room gets some of it's heat from the people in it and from other electronic devices (lamps, computers, etc.) In Canada we may also have a fireplace and other heaters.
The problem, especially in a tall room, is that the heat rises to the ceiling and does the people in it no good. By turning the ceiling fan on so that it blows upwards it takes that warm air and pushes it down the walls to the floor. By having blow in that direction you don't feel a draft as much.
For a very big room it may be better to have the air blow downwards, it will help keep the warm air down.

Saturday, September 24, 2005


A/C colder when turned off?

Question: Turn the air-conditioning on in the car for a while and feel the cold air coming out of it. Then turn off the A/C but leave the fan on, it's colder - isn't it. Why would the air get colder after you turn it off?

My guess is that when you turn the A/C off the motor stops working (and producing heat) but cooling plates are still cold (for a while). It's inevitable that the A/C unit dumps some heat from the engine and from the compressor etc. into the car. When you turn the A/C compressor off it stops producing this heat and for a while the air is cooler than with the A/C on.

Monday, September 12, 2005


How can we know if the light in the refrigerator goes off?

You close the door on the refridgerator and the little light is supposed to go off, but how do we know?

If you open the fridge, put your hand on the light bulb. If it's hot, then maybe there's a problem with the switch, but if it's cold and getting warmer it's because the light was off when the door was closed - easy.

Monday, August 08, 2005


Stealing coats

A department store had a problem where a shoplifter would come in, grab a armfull of coats off the rack and run off. What kind of things can the store manager do to prevent this kind of thing from happening?
By hanging up the coats so that the coathanger hook goes one way, then the other for every other item, it makes it difficult to grab a bunch of coats at one time. Although you could still easily steal, say, three by turning one hook around. The solution is not perfect but it doesn't cost anything to implement.

Sunday, July 31, 2005


Road reflectors

In some states in the US you'll see these neat little refectors embeded in the road. At night they are quite easy to see and don't fade like the lines in the road do. Also, if you veer out of your lane the bumps will give you feedback through your ears. Since these things are so great why doesn't every state have them?

Although these reflectors are great they only work in places where it doesn't snow. Once the snowplow goes by, it'll yank them out of the road or at least damage them, possibly damaging the snowplow as well.

Thursday, June 16, 2005


Chinese and alcohol

Some people of Chinese descent cannot handle alcohol, why might that be?

It's possible that we all used to have alcohol intolerance but as we started going into cities the danger in drinking the water increased. Drinking alcoholic drinks were safer than the water. Those who couldn't drink the alcoholic drinks were more likely to be killed off.
In China the practice of boiling water and adding herbs (tea) killed off the germs while boiling. There was less evolutionary pressure to become tolerant to alcohol.




You learn in school that gravity pulls you down at about 9.8 m/s^2. If you jump out of an airplane you would accelerate at this rate and in theory in about 30 seconds you would be going more than 1000 km/h. But in fact a skydiver only reaches about 200 km/h.


What you learn in school is the simple situation which has no air friction.
Air resistance is increases with the square of the velocity, as you go faster and faster the air resistance keeps increasing until it is a strong as your weight and stop your acceleration.
In other words, if you are heavier (denser) your terminal velocity will be a little higher.

-What would happen if air friction where only linear to velocity?


Shake, shake, shake

Why does shaking a closed carbonized beverage make it explode when you open the can?

Creating bubbles from nothing takes a lot of energy. Making a bubble larger, takes less energy. What you do when you shake the can is tiny bubbles, which can grow easily when you open it.
I believe the same thing happens when you freeze or nearly freeze the beverage. It's easier to grow the bubbles when there's some small particle to start it off from.

Bubble, Bubble Boil and Trouble

If you are very observant you will notice that a kettle of water will make more and more noise until it reaches a boil then that noise stops, why?

The noise you hear are bubbles collapsing. What happens is that the water near the heat heats up some water that goes to a gas (steam) and that little bubble starts rising to the surface. But it quickly encounters some colder water and the bubble collapses noisily.
Once all the water is 100 degrees C then the bubble is more likely to reach the surface and leave that way, which makes less noise.

Tuesday, June 14, 2005


Speed of light

The speed of light calculated in 1977 was 299,792,457.6 m/s. After 1983 it is 299,792,458 m/s exactly, how could that be?

At the 1983 General Conference on Weights and Measures they decided that since they have a definition of the second, they should define the meter as how far light in a vacuum can travel in that second. Using lasers and accurate clocks today allows us to calculate the speed of light very accurately. Before the length of a meter was defined by a bar in

Before (since 1791) the definition of a meter was 1/10 millionth of the length of the meridian of the earth along a quadrant. i.e. 1/40 millionth the circumference. This was not precise enough, so they made a new definition.

Magic Dave
Length Conversion Table.

Monday, June 13, 2005


Stars twinkle, planets don't - why?

If you look up at the "stars" you'll see that almost all of them twinkle, but if you know which are the wandering "stars" - the planets, you'll notice that they don't twinkle. Why is that?

Stars twinkle because the are so far away they are points of light. In other words, the photons of light come one after another in a straight line from the distant star or galaxy.
The planets are actually small disks of light so the light comes in parallel lines. If one of these 'lines' gets absorbed in the atmosphere there are still other 'lines' of light that can get through to your eye.
I suppose that there are some galaxies are big enough and close enough that they don't twinkle much either.

Where do our atoms come from?

When the universe was created in the big bang there were only two types of atoms created, Hydrogen (74%) and Helium (26%). Where does all the other types of atoms come from?

The heavier elements are fused through nuclear fusion.

Increase your lottery winnings

I tell you that I can increase your lottery winnings if you win, am I lying?

There's a good chance that I can increase your winnings if you win. Especially if I happen to have a database of numbers that people have picked in the past. Most people pick numbers that they identify personally with, like their son's birthday or wedding day. Most favorite numbers are below 10.
Since in a 6-49 type lottery (where you pick 6 numbers out of 49 numbers) people are unlikely to pick a sequence like 13-14-15-16-17-18, I might choose a number like that for you, it's just as likely as any other number and far fewer people would choose it for their lottery pick. This way when you win you are more likely to win alone and not split the prize, thus I increased your lottery win.

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