Dinner Questions

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

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

Hints:

• In most lotteries today more than one person can win.
• If more than one wins the lottery jackpot is split among the winners.
• Can I increase the chance that you are the sole winner?

Solution:
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.

Question:
You know that if you roll a six sided dice enough it'll average out to be 3.5 (1+2+3+4+5+6)/6, this is sometimes called the "Law of Averages."
Here's the theory, if you notice that you've been rolling a lot of low numbers in a row, since you know it's going to average out a lot of high numbers must come up soon.
This is what some people try to do with lotery numbers by keeping track of old lottery numbers to help predict future winning numbers.

Hints:

• Think of what would happen if the dice was swapped to a new pair of dice, or if the balls used in the lottery were changed, of you repainted the balls to be different numbers.
  
• Remember than dice and lottery balls don't have a memory.

Solution:
Although things should eventually average out it doesn't have to happen soon, or even in your lifetime. Just because you rolled a thousand ones in a row doesn't mean you are going to roll high from now on to average it out.
Basically, you need to remember that dice don't have any memory, they have no idea what you rolled before.

Question:
Take it as a given that large animals have more trouble keeping cool than smaller creatures. Why would that be?

Hint:

• Elephants have big ears to keep cool
• These ears are to increase it's effective surface area
• Think of how the volume of an elephant increases for every cm taller versus the increase in area

Answer:
It's sometimes called the "square, cubed law". As an animal gets bigger in one dimension (say taller) the surface area increases to the square but the volume increases to the cubed (which is much faster). The heat generated inside must escape through the skin (and through breath) but the ratio between surface area to volume keep decreasing as the animal gets larger.

Question:
We showed before that a fan should heat up a room, so how does it keep us cool?

Hints:

• It's not by refrigeration or like an air conditioner (or at least the effect is negligible).
• In Canada everybody knows about the wind chill effect.
• Most people burn about at about 100 Watts. This heat must go somewhere.
  

Answer:

We create heat, but if there's no wind we heat the air close to our skin and it sticks around, slowly moving away from us (upwards). This air insulates us, makes it more difficult to remove the heat made by our body (it radiates some of the heat back into our body as well).
The fan pushes the hot moist air near our skin with cooler drier air from the room and makes us cooler.
If the room is really hot, we begin to sweat and the wind helps us evaporate this sweat. This evaporation removes even more heat from our body.
Having a fan on in the room when no one is in it, is not very useful and wastes energy.
On the other hand, if a room is hot and the outside air is cooler a fan near an open window can help cool the room more quickly. (I'm not sure which direction the fan should point - should it blow the cold air in, or blow the hot air out?).

Here's a good link about how a fan works.

Question:
Does a fan heat up or cool a room?

Hints:

• We are assuming a stand up fan in the middle of the room
• Assume the windows are closed and the system almost a closed system.
• It's not a very closed system since we have electricity coming in the wall and into the fan.
• Prove that it heats up a room

Answer:
Since our room is closed and we have a motor that's working and getting electricity we should expect the room to heat up. If you put your hand on the motor after it has worked a while you'll see that it's a little warm. The room should heat up slightly with the fan turned on.

So how does a fan keep you cool?

Question:
If you had a bicycle with square tires, would there be any way to ride it?

Hints:

• The answer is 'yes', how?
• You would need a special road
• You would probably not be able to turn on this road

Answer:

Here's a page with a picture which explains it all. Basically, you would need a road that has bumps in a special shape. The tires would be aligned so that the corners would end up between the bumps. The special shape is an inverted catenary.

Question: When we ride a bicycle it's pretty easy to keep upright, but when we stop or even slow down it's difficult to keep upright.

Hints:

• There is more than one reason
• One reason is similar to why a spinning yo yo or rolling a hula hoop keeps in a plane
• The front wheel of a bicycle is mounted differently than the back wheel.

Answers:

• One reason is that when we are moving we can make small corrections to the sterring and balance that way, when we are going very slowly it's hard to do this.
• Then spinning wheels have a gyroscopic effect which helps keep the bicycle balanced automatically. Since the wheels are very light this probably isn't a major effect.
• The front wheel is mounted at an angle. This has a variety of effects. One is that you can let go of the handlebars and it won't try and turn right away. But also if you lean to the left, because of this angle the wheel will tend to turn more into the curve and will cause the bike to right itself automatically. It's like a self correcting feature of the bicycle.

Question:
When we sneeze we always close our eyes, why is that?

Hint:

• The answer is kinda gross
• It's not because we may get snot in the eyes.
• It's not because of some historical evolutionary accident.

Answer:
When we sneeze we actually build up pressure inside the body, partly because our lungs are a little leaky but also because we are using lots of muscles and build up liquid pressure under our skin.
There's a real chance that on a big sneeze if we didn't close our eyes our eyeballs would pop out.
-Told you it was gross.

Hmm, it could be that this explanation may be false:
see straightdope about this.

Question:
Is there a reason why clocks run clockwise?

Hint:

• Before clocks and watches people watched the sun to figure out what time it was.
• Clocks were first invented in Europe, which is in the northern hemisphere.

Answer:
A sundial's "hand" (the shadow) moves in a clockwise direction in the northern hemisphere. When clocks were first made it made sense to model the clock to what was used previously - the sundial.
In the southern hemisphere the sundial runs in the opposite direction.

Joke:
An American couple goes south to Mexico and forgot to bring their watch. They pass a local and ask what time it is. In front of the local, there's a donkey and he cups the donkey's balls and says that it's 11:30. The couple goes to lunch and after lunch they see the same Mexican sitting in the same place and the donkey is still there. Out of curiosity they ask the local again what time it is and he cups the balls of the donkey and says 12:30 señor.
The American's are amazed and ask the Mexican how he is able to tell the time by the donkey's balls?
The Mexican replies, "Ah não señor, it's because the donkey's balls are in the way and I can't see the clock on the tower across the plaza."