What is a good problem?

Part of the reassessment process has students pick problems to solve that they think are good demonstrations of their understanding of the material (or the standard).

For me (as the evaluator), I can learn quite a bit about what a student thinks just based on the problem they pick to solve.  However, it seems that students really don’t want to pick problems.  They would prefer to have me just tell them what problems to solve.

OK, let’s do this.  Let’s look at some problems and see which ones are good and which ones are not so good.  In this case, it will be for the Position-Velocity-Acceleration standard.  For this standard, students should show that they understand and can use the definitions of position, velocity, and acceleration in 1 dimension.  So here are some questions.  You get to pick which one is the best.  Actually, why don’t you score them from 0-10 (11 being the best).

Problem A.

A plane has a mass of 1120 kg and is landing on a runway.  The landing speed of the plane is 50 m/s and the runway is 2140 meters long.  What is the acceleration of the plane?

Problem B.

Your car is the fastest all around.  No one can beat you.  It has an acceleration of 8.2 m/s2.  Suppose you start from a rest (because, don’t all drag racers do this).  How long would it take your awesome car to get to a speed of 55 m/s?  What is this speed in mph?  What is the average speed during this time?  How far did you go?

Problem C.

A police car starts from rest and can accelerate at 5.5 m/s2.  The police car starts accelerating as soon as a speeding car passes by with a speed of 25 m/s.  Assuming the police car has a constant acceleration and the other car has a constant speed, where does the police car catch up to the other car?

Problem D.

Can you have a hang time of over 2 seconds when jumping?

Problem E.

A rocket is in space traveling with a speed of 328 m/s.  It fires its rockets to create an acceleration of -10.7 m/s2 (slowing down).  What is the speed after 5.8 seconds?

Problem F.

no words

 

Common problems on lab reports

After reading over the lab reports, there were several common problems.  Here is an overview.

  • Hypothesis. What exactly is a hypothesis?  There is an actual thing called a hypothesis and there is hypothesis testing.  However, just about every student that used this word used it incorrectly.  My suggestion is to just not use this word.  Instead, focus on model building.
  • “I learned a lot”. Remember, the report is about building a model. Hopefully you learned something, but it’s not really relevant in the report. I am only commenting on this because it was a very common statement in the reports.  Not sure why so many people stated this.
  • Human error. Please don’t use this term or any term similar to it. If there was a problem that human caused – just explain that problem. If it was a calculation error – how do you know it was a calculation error?  If the measurements were poor – just describe in what way the measurements were inaccurate.  Saying human error just glosses over the problem.  Repeat – never use this in your lab report.
  • “I proved that …”  Science doesn’t prove anything to be true.  If you drop a ball 1000 times and it falls, do you prove that balls fall?  No, because what if you drop it the 1001th time and it doesn’t fall.  You have shown that it is very likely to fall (or you have built a falling ball model) – but you didn’t prove anything.  On the other hand, you can prove things to be false.  If I say the acceleration is constant and just find one case where the acceleration changes, it’s ok to say you proved constant acceleration is incorrect.

Bonus video

  • Gather materials. I understand why this is in the lab report – but if you want to leave it out, that would be fine with me.  In general, I encourage students to write a lab report so that other students in the same lab could reproduce your results.  You can make assumptions that they have access to the same stuff you have access to.
  • Scatter plot instead of bar graph or line graph. There is rarely a reason to include a bar graph or a line graph.  You probably want a scatter plot.  If you don’t know the difference between these graph types – just make a graph on graph paper.
  • Graphs with linear fits and slope. Just about every time you make a graph, it should be to show a functional relationship between two things.  If this is a linear relationship, you can fit a linear function to the data (a best fit line).  Why include a best fit line if you don’t also include the slope of that line.  Might as well also put this slope on the actual graph.  In your analysis be sure to explain what that slope means (and the units for the slope).
  • Paraphrasing other students or other materials.  I made this clear in class, but if you are just paraphrasing something – that is copying.  Don’t copy.  Write your own words.
  • Misspelled words. Why?  Why are there spelling errors in your lab report?  I assume you are using some type of word processor.  Don’t these programs tell you when something is spelled incorrectly?
  • Self Edit. Don’t write something and then just move on.  This lab report is going to be turned in for an actual grade in a real class.  Take the time to go back over what you wrote – or have a peer or tutor also look over your lab.  It might help to write something and then take another look at it the next day.  Looking at student reports, it’s very clear that some of you just wrote stuff without reading it.
  • “Overall, this was a fun lab”.  I’m glad you had fun – but what about your physics model?  Again, just focus on the model.  Now – this doesn’t mean that you have to be all stuffy and formal.  Feel free to write in any style that you like – but in the end it’s your model and the analysis of your model that really matters.

Pi Day Posts

Below are all of my previous Pi Day posts (at least the ones I can find)

Seatbelts are bad

I’m not going to wear a seatbelt anymore.  Here’s why:

  • The seatbelt is uncomfortable.  It rubs weird on my shoulder.
  • I was talking to the guy that changes my oil.  He said that he knows a guy that was in a car accident while wearing a seatbelt.  The seatbelt didn’t prevent the accident – but he did get trapped in the car because of the seatbelt.  Important point: this oil change guy is IN THE AUTO INDUSTRY.
  • I didn’t wear a seatbelt at all last year and I never got in an accident.
  • Sure, you BELIEVE that seatbelts save lives, but I BELIEVE they are bad for you.
  • What about before 1968?  All cars didn’t have seatbelts then.  People just used their natural defenses to keep them safe.
  • There are long term effects to wearing a seatbelt.  If you drive a lot with a seatbelt, your left shoulder won’t be as tan as your right shoulder.

I’m kidding.  Wear your seatbelt and get a flu shot.

MythBusters Blog Posts

Here are some of my previous blog posts dealing with the MythBusters show.

Python Tip: User Scrolling

Just another quick tip.  Sometimes I create python to use as a demonstration. Here is an example:

https://trinket.io/glowscript/717bedba81

This is a double pendulum (sorry for the lack of embeds – I hope to fix that soon).  But there is a problem when you use the code as an embedded demo.  What happens if a user is reading over a blog post using the scroll wheel?  If they mouse over the trinket embed and scroll, they will zoom out and not see anything.

You can fix this by adding the following:

Yes, just add scene.userzoom=False

That’s it.

Python tip: Pausing

Ok, I’m going to start writing down things I learn about VPython.  First, a note.  If I say “VPython” or “Glowscript” – I’m really talking about the same thing.  In my usage, I will let VPython be a program in python with the visual module.  Hopefully, these things that I write will be the same for both platforms.

Now for today’s tip – how do you pause a program?  In the past, I have made these “start”-“pause” buttons.  It’s not super difficult to do, but there is some stuff in there that I just don’t understand. But there is a better way.

Let me start with a sample program.  This is just a ball tossed in the air – but with a pause button. Code here.

The magic happens in line 11.  When you put that scene.pause() in your program, you get a big “play” button in the lower right of your output window.  In this case, the program is paused before the calculations start so that the play button is there at the beginning.

Of course, you could have some calculations and then the pause button – it just depends on what you are trying to do.

iPhone Physics

Three Keys to Success

This isn’t a normal physics post. In fact, I don’t think there will be any physics in this at all. Instead, I am writing a note for my oldest daughter. She is getting close to college-age so there are some important things she should understand. Maybe this will be useful for others, so here it is.

You are getting ready for next step in learning—going to college. But where should you go? What should you study? Really, I have no idea about that. What I do want to address is the following statement from you.

I got a letter from University of ABC, and I think that’s pretty cool. However, I’m not sure I could be successful there. It seems out of my league.

Hopefully you noticed that I made up the name of the university—I don’t want to offend anyone for not mentioning their favorite institution. Ok, but I want to address the issue of success. Although that can be something difficult to measure, you still want to be successful. Here are the three things that really matter when you start something new.

1. Your Starting Point

This is a little sad, but unfortunately true. The best way to be successful is to start off as successful. Sure, we don’t want it to be this way. We want this to be the land of opportunity where everyone has a chance to do great things. But that’s just not true. If you don’t have access to affordable higher education, what will you do? What if you have to work at a full time job at the same time you are taking classes? Do you think you will learn as much as someone that focusses just on the class? Finally, what if you go to an exclusive university and make some connections with very influential people?

I’m not saying that we have to change this system, but it’s important to know what you are dealing with. You need to know the rules of the game. You also need to know that some people are successful for reasons that are out of your control. You can’t do anything about where you start in this game, you just have to start.

2. Luck

Sometimes in sports the ball will take a lucky (or unlucky) bounce and this can be the deciding factor in a crucial game. It happens—ok, there are some sports that don’t have balls, but you know what I mean. Luck can be both good or bad, but it’s there.

Luck can be a big part of your success—and the best thing is to acknowledge the luck-factor. How about an example? I really enjoyed my time as the science advisor for MythBusters. It was a great opportunity and I think I made significant contributions. The same is true for my science role in MacGyver. But is it possible that someone else could have done this job and maybe even been better at it than me? Absolutely. The truth is that there was an element of luck that got my into both of these projects—and that’s ok to admit.

There will undoubtedly be cases in the future that don’t end up in your favor. That’s also ok. Don’t worry about it. Just keep moving on and doing what you do. You can’t control luck—if you could it would be called something else.

3. Talent

Now we are at the part that most people think of that leads to success. But what is talent? Let me give a few examples:

  • Playing a piano or some other musical instrument.
  • Writing.
  • Mathematical talent.
  • Computer programming.
  • Fixing things.
  • Athletic abilities.
  • Determination.

Of course you could come up with some more (like nunchuck skills) if your favorite talent isn’t listed. Also, you might argue that some of these talents are really just luck based on the way your were born. Ok, that also might be true but I am not going to say that. If it was only about luck, what would be the point of trying?

But I don’t want to talk about how your talents make you successful. I know that you have talents, there is no question about that. However, there will be times when you don’t succeed in spite of being talented—and that’s ok. Really, the problem is with people who have never failed. Without failing, we don’t grow as humans. So yes, failure sucks—but it’s not the end (well, not usually).

Perhaps the most important thing to take from this is to be brave. Don’t worry too much about the future—it’s going to happen whether you want it to or not (unless one of your talents is the ability to control time). Don’t be afraid to try new things and don’t stop something for fear of failure. Just keep moving forward. It’s what we humans do.

Science Fiction Physics

Star Wars

Science Fiction