Dinner Questions

Q: Most e-mail scams are really bad. Full of typos and other hints that it's a scam. Why?

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.

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

• Our sense of smell works by hundreds of olfactory receptors.
• Each receptor is encoded with a different gene.
• Each receptor is folded a special and intricate way to detect the odor. 

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.

- 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.

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.

Labels: math

Question:
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?

Hint:

• The freezer is often quite dry.
• You ice cubes have usually been there for a while.
• Just because it's cold doesn't meant that things won't evaporate.

Answer:
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).

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

Hints:

• The main reason isn't to recover a dropped item, like a ring, although it helps with that.
• Sewers stink.
• Bugs are attracted to smells.

Answer:
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.

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

Hints:

• Hot air rises.
• If the fan is blowing air down, it's to cool a room
  
• If it's blowing up, it's to heat a room.
• If the fan is blowing up too hard it may make the room feel colder.
• Works best if the room is big and tall.

Answer:

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.

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?

Hints:

• Refrigerators and air-conditioners use energy to take heat from one place and put it in another.
• So there's a part that's cold and a part that's warm, the warm part is usually dumped in the air (outside).
• Air-conditioners have motors that are hot as well.

Answer:
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.

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

Hints:

• Think of being the first one to open the fridge in the morning,
• What happens if the light has been on for a while?

Answer:
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.

Question:
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?
Hints:

• My solution doesn't prevent the shoplifter from stealing, just makes it harder to steal a lot.
• My solution doesn't require any hardware (or software) to implement it.
• You can prevent it just by changing a procedure
• By changing the way the coats are hung on the rack.

Answer:
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.

Question:
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?

Hints:

• Canada doesn't have them.
• The northern states don't have them.
• Places where it snows usually don't have them.

Answer:
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.

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

Hints:

• About 50% of Chinese, Japanese or Taiwanese people have alcohol intolerance. If they drink too much (for some just a few glasses) they probably will have to go to the hospital.
• Think of an evolutionary reason.
• The Chinese invented tea a long time ago.
• Beer and wine has (or used to have) yeast that are alive.
• In larger cities it often became safer to drink beer than water, because the water could contain germs that can kill you. With beer the yeast has killed off these germs.

Answer:
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.

Links:
http://www.allergyclinic.co.nz/guides/54.html

Question:

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.

Hints:

• The skydiver accelerates for a while then slows the acceleration, and then stops accelerating at a terminal velocity.
• It has to do with the air resistance of course
• Air resistance increases with the square of the velocity (basically), there's a cubed component as well that it usually ignored.

Answer:
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?

Links:
Hyperphyics.

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

Hints:

• The pressure inside the can remains basically the same (unless you heat it, say). So shaking the can doesn't increase the pressure.
  
• Freezing, or nearly freezing the beverage often has the same effect.
• When nearly freezing you'll get tiny crystals in the beverage.

Answer:
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.

Question:
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?

Hints:

• The noise is made by bubbles
• How is it different before it starts boiling vs. after it's boiling?
• It's different because when it's boiling, all the water has reached 100 degrees centigrade.

Answer:
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.

Question:
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?

Hints:

• A second is now defined as x many transitions of a Cesium-133.

Answer:
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.

Links:
Magic Dave
Length Conversion Table.

Question:
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?

Hints:

• Twinkling is caused by the starlight interfearing with the atmosphere.
• Some of the starlight gets reflected, absorbed or bent by the atmosphere.
• The stars are very far away, the planets are not so far away.

Answer:
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.

Question:
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?

Hints:

• The center of our sun creates a lot of energy from nuclear fusion.
• Nuclear fusion happens when two or more nuclei combine to become a larger one..
• Simple Hydrogen fusion makes Helium.
  

Solution:
The heavier elements are fused through nuclear fusion.

• Small stars (smaller than ours) can only produce Helium from Hydrogen.
• Medium sized stars (like our son) eventually 'burn' away their Hydrogen and can produce heavier elements like Carbon and Oxygen.
• Large stars (greater than 5 times our sun) can produce nearly? all the elements up until iron. It can't produce anything heavier than Iron because it takes more energy to make a heavier element than it gets out in energy from the fusion. The other reactions are all exothermic, producing more energy than was required to fuse the elements together.
  
• These large stars explode in a supernova explosion and during the explosion heavier elements than iron are also created. This is where we come from, from older supernova explosions! We are literally made of star dust.
  

Sources:
http://www.enchantedlearning.com/subjects/astronomy/stars/fusion.shtml
http://en.wikipedia.org/wiki/Nuclear_fusion
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hydhel.html