## Sunday, July 04, 2010

### The World Is Flat And the Answers Make It Flatter

I don't know what to make of this news article. It is also early in the morning on a Sunday after a late night, so my brain may not be functioning just yet. So I'll let you figure this out for yourself.

The news article describes the effort to educate middle-school teachers in trying to correct misconception that students have on a few issues with our physical world. This is a very good effort because what better way to discuss physics than to talk about things we understood either incorrectly, or for the wrong reasons.

Middle school students in Springfield and elsewhere are not receiving an adequate science education, says Robert A. Barkman, a Springfield College professor of biology and education.

Barkman has developed a program called “The World is Flat” to help middle school teachers learn how to identify students’ misconceptions about the physical sciences and then give them the tools to correct them.

But what caused me to wake up and rubbed my eyes were the answers given to some of the questions that were used to test people's understanding. The answers are not outright wrong, but they do raise some eyebrows. I'll tackle each one of them individually and see if you agree or disagree with me, or if I'm just being picky.

Many middle school students fail to answer these questions correctly.

Q. You drop two weights from the same height. Weight A weighs 10 lbs and weight B weighs 50 lbs, but they are identical in size and shape. Which will hit the ground first?

A. They both will fall at the same speed – the speed of gravity. Weight does not affect terminal velocity.

First of all, any physics student can tell you that the "speed of gravity" is either c, or not yet verified but theorized to be c.

Secondly, we kinda know what the answer is trying to convey, but really, does it have to be put in this manner? What it can and should say is that both objects (neglecting air resistance), will fall at the same ACCELERATION and will hit the ground at the same time. That is correct and accurate enough at this level.

Thirdly, since when is the terminal velocity not affected by the weight? Why is this even mentioned here since the original premise is that air resistance is negligible here? Very puzzling.

Q. You are at a playground in winter. You touch the ladder, which has wooden supports and metal rungs. Which material has a lower temperature?

A. They both have the same temperature. The metal rungs may feel colder, because they conduct heat better. They draw the heat from your hand away faster, so it feels colder, but if you measured them with a calorimeter, they would have the same temperature.

Er... the answer is correct, but how does one measure "temperature" with the simple calorimeter that are used in most schools? A calorimeter measures the amount of heat exchange, which involves the specific heat capacity of the object. So if you put the same volume of object (wooden and metal rungs) into a container of water, even if you have perfect insulation, the equilibrium temperature of the water at the end will be different for both. This is because the wood and the metal have different heat capacity.

Q. On planet Earth, an objects weighs 150 lbs and has a mass of 400 kg. On the moon, it weighs 140 lbs. What is its mass on the moon?

A. The same as it is on Earth. Weight is affected by gravity, but mass remains constant.

No problem here.

I'm not sure if the answers offered in the news article are the ones that were given to the teachers. I hope not, since, from the news article, it appears that the courses being given have more to do with self-discovery than being told what the answers are. So one would hope that the teachers discover the answers for themselves.

Zz.

#### 4 comments:

Blaise Pascal said...

Q. On planet Earth, an objects weighs 150 lbs and has a mass of 400 kg. On the moon, it weighs 140 lbs. What is its mass on the moon?

Was this question copied correctly? I get the impression this is not the Earth/Mood system and/or Imperial measurement system I'm familiar with.

ZapperZ said...

It was copied correctly (you can check the article yourself). But you're right, the mixing of the units is utterly confusing.

I think I paid more attention to the explanation of the answer than the numbers. This question, now that I'm looking at it again, is horrible with the way they asked it.

Zz.

rwuncertainty said...

The acceleration due to gravity on the surface of the moon is 1.6m/s^2. So, if something weighs 150lbs on Earth, it will weigh (1.6 m/s^2)/(9.8 m/s^2) * (150lbs) = 24lbs on the moon, not 140lbs.

Moreover, simply telling students that science disagrees with their preconceptions seems to chase them away from scientific thinking. Teaching science is trickier than that:

http://rwuncertainty.wordpress.com/2010/07/03/when-your-preconceptions-disagree-with-the-evidence/

Doug Natelson said...

How the hell can something with a mass of 400 kg have a weight on the earth of 150 lbs? Is it in an elevator accelerating downwards at 6/7 of a g?