Page 21 of 27

Bonus: Fixing a Kenmore 44072 Washer with F03 Error

rhettallain Leave a comment

This is not a “fix-it” blog. However, I think the Internet should be a useful friendly place. Think about the times you have had a problem. The Internet has been there for you – right? I remember not too long ago, I was trying to set up iChat video chat with my brother-in-law and his brand new iMac. I was 3 states away and it was getting frustrated. In the end, my friend the Internet helped me. Problem solved. Everyone one has found a perfect solution for a particular problem on the Internet – right? So, this bud’s for you Mr. Post-obscure-stuff-in-the-hopes-that-at-least-one-person-finds-it-useful guy. Right. So, this isn’t really physics or science like my normal stuff.

Here is my washer. It makes my family happy. They like clean clothes. Kenmore 44072 Front Load Washer.

Well, my wife went to wash clothes and the front display says F03 Error. Me: ER? So, I look it up on the Internet. Here is the site I found from [fixya.com](http://www.fixya.com/support/t629840-kenmore_44072_front_load_washer_drain). Ok, it appears it could be something stuck in the drain hose. There was definitely water in there. I tried a couple of things, but finally decided to take off the back of the machine and look inside (unplug it first). I followed the hose to the pump and there is this squishy rubber bag connected to the pump. I squeezed it and sure enough, something was in there.

It wasn’t trivial to get all the water out of the machine without the pump. At first I lowered the drain hose into a cup a little at a time. Finally, I hooked my wet-dry shop vac up to the hose and sucked the water out. (everyone needs a wet-dry shop vac). Anyway, I took off the “pump bag” – not sure what it is called, but here is what it looks like:

![Screenshot 50](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-50.jpg)

The pump bag had one of those annoying metal clamps holding it on – you can see the same kind holding the drain hose to the pump. When I removed the bag, more water came out. Here you can see something stuck in the pump.

![Screenshot 51](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-51.jpg)

I pulled that sucker out. Here is the stuff I found:

![Screenshot 52](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-52.jpg)

I put everything back together, and it seems to work. Do not ever try this. Don’t ever open your washer. Don’t try to fix things. See, I told you NOT to do that. It’s dangerous, you could break something. (now you can’t get angry if something goes wrong).

Spring Motion and Numerical Calculations

rhettallain 2 Comments

Maybe you know I like numerical calculations, well I do. I think they are swell. [VPython](http://vpython.org) is my tool of choice. In the post [Basics: Numerical Calculations](http://blog.dotphys.net/2008/10/basics-numerical-calculations/) I used vpython and excel to do something simple. I will do that again today (in that this problem could also be solved analytically). However, there is one big difference. This problem has a non-constant forces. Suppose I have a mass that is connected by a spring to a wall. This mass-spring is sitting on a table with no friction.

![Screenshot 27](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-272.jpg)

There is a very interesting property of springs. The more you stretch them, the greater the force they exert (in the usual model of springs). This model works very well.

![Screenshot 28](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-282.jpg)

This is known as Hooke’s law. I have written it as a scalar for simplicity. The “k” is called the spring constant. It is a measure of how “stiff” the spring is. The value “s” is the amount the spring is stretched. Typically, there is a minus sign in front of the ks to indicate that the force is in the opposite direction that the spring is stretched. Really, in a scalar equation this is rather silly to include (but everyone does anyway).

**Question: What will the motion of the mass be like if I pull it back and then let go?**

Although this can be determined analytically, I am going to first calculate this with vpython. I will try to show all the details so that you can reproduce this also. If you have not already installed [vpython](http://vpython.org), do that now (don’t cost nothing).

Continue reading “Spring Motion and Numerical Calculations” →

Basics: Numerical Calculations

rhettallain 4 Comments

**Pre Reqs:** [Kinematics](http://blog.dotphys.net/2008/09/basics-kinematics/), [Momentum Principle](http://blog.dotphys.net/2008/10/basics-forces-and-the-momentum-principle/)

What are “numerical calculations”? Why are they in the “basics”? I will give you really brief answer and then a more detailed answer. Numerical calculations (also called many other things – like computational physics) takes a problem and breaks into a WHOLE bunch of smaller easier problems. This is great for computers ([or a whole bunch of 8th graders](http://blog.dotphys.net/2008/09/computational-physics-and-a-group-of-1000-8th-graders/)) because computers don’t mind doing lots of little problems. Why are they “basic”? Well, most text would say they are not basic. I disagree. I think this is a legitimate method for solving problems. In particular, this is a great way of solving problems that can not be solved analytically (meaning solving one hard problem).

**Numerical Calculations are Theoretical Calculations**

Let me just get this out of the way. Numerical calculations and analytical calculations are really in the same “class”. Often people will lump numerical in with “computational experiment” but that is a really bad thing to do. Some others will claim that there are three different “paths” to discover stuff in science: theory, experiment, and simulations. Simulations are the same thing as numerical calculations which are the same as theory. ([I wrote a letter about this in the American Journal of Physics](http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000076000009000797000001&idtype=cvips&gifs=yes))

**Example Problem**

Let me start with a problem that can be solved analytically. Suppose I have a ball of mass 0.5 kg and I throw this straight up with a speed of 10 m/s. How high will it go?

Continue reading “Basics: Numerical Calculations” →

Fun things to do with a green laser pointer

rhettallain 1 Comment

I went home for lunch today. While waiting, I saw this lizard. We have many lizards in Louisiana, I like them, really I do. So, this is what I did:

No lizards were harmed in the filming of this video.

I was really surprised. I thought for sure that I had tried this before and nothing happened. Maybe it was because of the white surface the lizard was on. Maybe it was because it was an older and wiser lizard (it was larger than normal). Maybe this is already a well known fact about lizards and laser pointers. Needless to say, this was quite entertaining and completely justifies the cost of my laser pointer.

‘Weapon Masters’ doesn’t understand floating

rhettallain 2 Comments

There is this show “Weapon Masters” – I think it comes on the discovery channel. It is not a bad show. The basic idea is that they have this history guy talk about the historical aspect of some type of weapon and this other guy tries to make an improved version. Last night the goal was to recreate the original flame thrower mounted on a boat.

They found a boat and they needed to test it’s sea worthiness. The builder guy (sorry, I don’t know his name) estimated that they would have 1000 lbs of equipment in the boat. To simulate this weight, they put 4 guys and two barrels of water in the boat and motored around.

After a little bit, the history guy noticed one of the barrels was leaking water. *”Quick! Put your finger in the hole before we all sink!”* he said. This is where he doesn’t understand floating. I think I can explain his error with two simple pictures:

![Screenshot 05](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-051.jpg)

The first picture has the boat with the water in the barrel. The second picture has some water that has leaked out. Either way, the total mass of water in the boat is the same. If you would like to talk more about floating, [here is my post about MythBuster’s lead ballon](http://blog.dotphys.net/2008/09/mythbusters-how-small-could-a-lead-balloon-be/) – same idea.

I think the weapon master history guy should have said:

*”Quick! Plug the hole before my shoes get wet! But, we won’t sink because the mass of water is the same no matter if it is in the barrel or in the boat.”*

Basics: Forces and the momentum principle

rhettallain Leave a comment

**Pre reqs:** [Free Body Diagrams](http://blog.dotphys.net/2008/09/basics-free-body-diagrams/), [Force](http://blog.dotphys.net/2008/09/basics-what-is-a-force/), [Kinematics](http://blog.dotphys.net/2008/09/basics-kinematics/)

The time has come to look at things that are NOT in equilibrium. The most basic question to ask yourself is: *”What do forces do to an object”*? Aristotle would say that forces make things move. Constant forces make things move constantly. Actually, Aristotle said there were two types of motion:

  • Natural motions: These motions don’t need anything to happen, they just do. Example: a rock falling. You don’t need to do anything to it. Example: fire rising. It just rises. (there was more to it than that, but you get the idea).
  • Violent motions: These motions are due to some interaction that forces them from their natural state. The natural state of a cart is to be at rest. If someone pushes on it, it will move. When you stop pushing (stop the violent motion) it returns to its natural state – at rest

I am talking about Aristotle, because these basic ideas are what most people think. If you push something it moves. If you stop pushing, it stops. And these people are correct. The problem is that there is always this extra force that no one thinks about – friction. Without friction, the rules change.

**New Rules (Newtonian ideas)**

If you push something with one force, it changes velocity. If you stop pushing, it stays at a constant velocity.

If you want to test your feelings for force, [try this force game I made on Scratch](http://scratch.mit.edu/projects/rhettallain/285748). The idea is that you need to move the box to the red circle. The arrow keys exert a **force** on the object.

Continue reading “Basics: Forces and the momentum principle” →

MythBusters – a tree is 90% air

rhettallain 1 Comment

Dear Mythbusters. I hope you know that I think you are awesome. I know you are not scientists, but rather master robot builders. I respect that. I envy your robot-building abilities. Please forgive me for pointing this out – but even if a tree is 90% air, that does not mean a ball has a 90% probability of passing through it.

For those of you who are unaware, in the last episode of MythBusters, they explored the idea that a golf ball should pass through a tree 90% of the time. What if they were to test following alternative myth:

*A golf ball has a 90% chance of passing through something that is 90% air.*

Here is my test object:

![Screenshot 05](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-05.jpg)

It is a steel box with air inside. I did not give the dimensions, but you can imagine it would not be difficult to make this 10% steel and 90% air. What would happen if I hit a golf ball at this? I think there were would be a 0.000000000000000000001% percent chance of it going through (smaller than that – but I think you get the idea).

What is really important is the scattering cross-section, not the density.

Letter to High School Students: What to Major in

rhettallain 2 Comments

Dear High School students,

How are you? I am fine. I am very glad that I am no longer in high school. Maybe you enjoy high school, but for me, it was not so good. Don’t get me wrong, I went to an excellent high school (Waubonsie Valley HS). There was something in high school that didn’t feel right. Maybe it was being in classes for too long and the lack of time to work on my own projects. Maybe it was lack of freedom in choosing my own classes (there was some freedom to chose). Or perhaps I was just not mature enough to enjoy it. Needless to say, I am past that now.

I think now, how could I help high school students? In particular, how could I help them choose a major in college (if they choose to go to college). So, this will be the topic of this letter today. Please don’t hope that I will write more useful high-school letters such as “how to find a prom date”. That is definitely one area I failed at.

Choosing a major is difficult and even scary. In a way, you are choosing a career – but maybe not as much as you think. First, choosing a major is somewhat a random event. Suppose you choose underwater basket weaving as your major for some reason. It is likely that you have never woven a basket underwater. Maybe you will like it, but maybe you won’t. You won’t really get a good idea of how much you like or dislike underwater basic weaving until you actually go underwater and weave a basket. Unfortunately, the underwater basket weaving curriculum has you taking UBW 101 (Introduction to underwater basket weaving) your sophomore year. You first have to take the pre requisites, history of baskets and introduction to water. After you decide you don’t really like this major, it has already been 1-2 years. So, if it takes you 5 or 6 years to graduate, don’t worry TOO much. Your parents may be displeased, but tell them I said it was ok.

**Major in Physics**

I know. You saw that coming. Why should you major in physics? Here are some of my points:

**It is difficult**

Wait. BECAUSE it’s difficult? Shouldn’t you do something because it is easy – not difficult? Well, it depends on why you are doing it. If you are doing something to improve yourself, difficult is good. Imagine you were going to exercise. Should you walk around the block or run 3 miles? Well, if you find that walking around the block is very easy, it probably won’t do much for you. If you find underwater basket weaving to be easy, maybe it is not really helping you grow. So, physics IS difficult, but that is a good thing.

**What else are you going to do?**

I hate to be a negative person (I am not really) but look at where we are today. There are financial problems, energy problems, problems with that rick-roll stuff. What are we going to do? You could help. Maybe it will be you that contributes to the energy problem (well, we all contribute to the problem, maybe you could contribute to the solution). Physics gives you are start in the fundamentals of nature. We NEED people to understand the basics so that we can defeat the energy problem.

What are your other options? Underwater basket weaving? Maybe there are lots of people who can do underwater basket weaving. This means there are lots of people capable of UBW (underwater basket weaving). Job competition for UBW is high and maybe companies will just start sending their UBW tasks to India where it costs less. Plus, does anyone really NEED UBW? Maybe it is the first thing to go when the economy is taking a turn for the worse.

**Are you ready for physics?**

A common idea that comes up is that students think they can not major in physics because they did not take physics in high school. I don’t think this is a disadvantage in any way. In introductory physics, the common problem is that students must “*unlearn what they have learned*” such as the idea that *constant force causes constant motion* (just to be clear -that idea is wrong). What about math? Yes, you need to be proficient in math. Most students entering school (at least here) are not quite where they need to be in terms of math understanding. However, that doesn’t mean they can’t catch up. Ideally, students should be ready to take Calculus I when entering college. You have time, work on your algebra and trig skills so that you can do well on the Math part of the ACT and place into Calc I.

**Other**

This is longer than I usually write without including an equation, so maybe this is a good place to stop. If you want to major in physics, there are lots of things to consider. Here are some resources:

Fake vs. Real Forces

rhettallain 2 Comments

In this post, I am going to talk about real and not real forces as well as the fake centrifugal force (if you don’t like the word “fake” you could replace that with “fictitious”)

First, an example: suppose you are in a car at rest and press the gas pedal all the way down causing the car to accelerate. What does this feel like? If I weren’t skilled in the art of physics, I might draw a diagram something like this:

![Screenshot 20](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-20.jpg)

Yes, maybe someone would add gravity and the chair pushing up, but this shows the important points. What is this force of acceleration? What causes this? This is EXACTLY the same thing as centrifugal force. If you think centrifugal force is real, this also should be real. I think this is enough discussion to show that this force (and centrifugal) is not real, but I will continue. There is another mystery: why does it feel like there is a force pushing you back when you accelerate? (if you have read all my blog posts, you may have a hint to the answer).

Continue reading “Fake vs. Real Forces” →

People need to play with magnets

rhettallain 2 Comments

Question from class: *What do magnets interact with?*

Basically, everyone said “metals”. I am quite surprised. No one specifically indicated that magnets only interact with iron and steel (of the materials they would likely see). I understand that steel is a very common material they are likely to encounter, but what about aluminum? I think this points to the idea that very few of my students have actually played with magnets. This is a shame. Everyone loves magnets.

So, I propose you go out and give someone you love some magnets today.