Grades are in. So, let me just say a couple of trends that I saw on the physical science final exam.
Gravity on the moon
I asked the question: “why is the gravitational force on an astronaut less on the moon than on Earth?”
The simplest answer is that the gravitational field on the moon is smaller than on Earth (I would accept that answer). Why is this? It is because the moon as a much smaller mass even though it also has a smaller radius (that idea is rather complicated for this class – that gravitational force depends on both mass and radius). I would also take “the mass is smaller” as a correct answer.
The most common incorrect answer for this question was that the gravitational force was smaller because the astronauts are farther from the Earth. As you get farther from the Earth, the gravitational force gets smaller. I see where this is coming from. In a sense, they are correct – especially if they answer only regards to the Earth. I think the big problem here (other than my question which could have been worded better) is that students think of gravity as something that has to do only with the Earth.
Energy is a buzz word
This isn’t just on one question, it was all over the place. Students love them some “energy” words. To them, “energy” is the duck tape of words. You can use it for anything. For scientists, energy is just energy. For students, it can be used for any of the following:
- electric charge
- electric current
Sure, you could argue some of those are forms of energy, but you would still have to use it correctly.
Density, mass, volume
I tried to pick some objects that would be clear. Here is the question:
Consider a small marble and a large styrofoam cooler. Which has a greater mass? Which has a greater volume? Which has a greater density?
The correct answer is that the cooler has a greater mass and volume, but the marble has a greater density. I think the biggest problem here is that students think that if something has a greater density (which is a ratio), it must also have a greater something else (mass or volume – you pick). Really, every possible combination of answers was seen on the tests. I think some really think the marble is more massive than a styrofoam cooler, I guess that might be an understandable mistake if didn’t actually pick both of them up. Maybe I should have picked better objects. I thought those would be clear.