Dinner Questions

How does a train stay on the track?

2009-06-28T15:55:00.002-03:00

- 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.

Find out a way to get the area of triangle.

2008-03-31T16:45:00.005-03:00

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.

Why are ice cubes small?

2005-10-03T16:44:00.000-03:00

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).

Ess curve on drains

2005-09-30T15:52:00.000-03:00

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.

Ceiling fans can heat the room too?

2005-09-30T09:20:00.000-03:00

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.

A/C colder when turned off?

2005-09-24T11:39:00.000-03:00

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.

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

2005-09-12T15:21:00.000-03:00

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.

Stealing coats

2005-08-08T19:33:00.000-03:00

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.

Road reflectors

2005-07-31T00:17:00.000-03:00

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.

Chinese and alcohol

2005-06-16T13:46:00.000-03:00

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

Ahhhhhhhhhhhhh!

2005-06-16T11:09:00.000-03:00

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.

Shake, shake, shake

2005-06-16T11:00:00.000-03:00

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.

Bubble, Bubble Boil and Trouble

2005-06-16T10:52:00.000-03:00

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.

Speed of light

2005-06-14T11:26:00.000-03:00

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.

Stars twinkle, planets don't - why?

2005-06-13T17:39:00.000-03:00

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.

Where do our atoms come from?

2005-06-13T16:32:00.000-03:00

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

Increase your lottery winnings

2005-06-13T16:24:00.000-03:00

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.

Law of averages

2005-06-13T16:06:00.000-03:00

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.

Why do elephants have big ears?

2005-06-07T18:35:00.000-03:00

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.

How does a fan keep you cool

2005-06-07T11:32:00.000-03:00

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.

Fan heats up

2005-06-07T11:20:00.000-03:00

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?

Would it be possible to ride a bike with square tires?

2005-06-07T11:12:00.000-03:00

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.

How come it's easy to balance on a moving bicycle and not a stopped one?

2005-06-06T15:13:00.000-03:00

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.

Achoo!

2005-06-01T09:50:00.000-03:00

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.

Why do clocks run clockwise?

2005-06-01T09:33:00.000-03:00

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."

What causes the seasons?

2005-05-31T19:07:00.000-03:00

Question:
What causes the seasons:

Hints:

It's not because we are closer to the sun in the summer.
There are two reasons it's warmer in the summer and both are caused by one other reason. (name all three for a bonus!)

Answer:
If you had to give one reason it's because the earth is titlted 23.5 degrees relative to the ecliptic (the plane that the earth rotates around the sun in).
This causes two effects, one is that the sun is up for longer during the summer than it is in the winter. This gives the sun more time to heat the ground than in the winter. But this is not the most important reason.
The most important reason is that the sun is higher in the sky, and points down more directly. Imagine flashlight in your hand and you point it straight down to the ground. It makes a small, bright circle of light. If you tilt the flashlight it'll make a larger, duller oval of light. But the amount of energy is the same from the flashlight it's just spread over a bigger area.
Note also that the sun doesn't heat the air or the clouds (or very little) it heats the ground (or the water) and the ground heats the air.

Bus Ride

2005-05-31T19:00:00.000-03:00

Question:
You are riding a bus, where's the best place sit on the bus for the most comfortable ride?

Hints:

We're talking about the up and down (bumpy) part of the ride.
We're asking is a seat near the front, middle, back or over one of the wheels is the best location.

Answer:
I'd say that sitting in the middle should give you a more comfortable ride.
The reasoning is that if you are over the back wheel, say, you get the amplitude of the bumps over that wheel. If you are further back, you get the amplitude plus a bit more because of the lever effect. If you are in front of the back wheel you get less amplitude (lever again).
Unfortunately, both wheels are bouncing so the best you can do is average the two by being between them.

Transferring the Ransom

2005-05-31T18:04:00.000-03:00

Question:

You kidnapped something or someone and they have agreed to give you the money. How do you transfer the money without getting caught?

Hints:

You don't want the cops to be able to follow you
Paris has a very complex sewer system

Answer:

One solution was to tell the cops how to wrap the money in a waterproof container. Then have them go to a phone.
From that phone you are told to go to a street.
Then you are told to throw the package in the sewer on that street corner.
The water carries the package away, but the sewer system is so complex it is difficult for the cops to know where it'll go and where you'll picked it up.
But you already tested it by throwing similar packages in the sewer and seeing where it comes out.

Intro

2005-05-31T14:09:00.000-03:00

The basic idea of this blog is to record some dinner time questions for your kid(s). Relatively easy questions that make you think, that may have several answers.