# True or false questions for density

1. Nov 9, 2015

### maximus123

Hello, I'm a trainee teacher and I'm delivering a lesson with a practical where the students find the densities of various objects. I want to end the class with 8 to 10 true or false questions about density which test misconceptions on density. The one I have is

Is a dense object always heavy?

If anyone has any suggestions on others I could ask I would be very grateful.

Kind regards

2. Nov 9, 2015

### Staff: Mentor

Very fun question.

"Using only a Beam Balance, how can you determine which object is denser?"

"Using only plastic grocery bags and a swimming pool, how can you determine which object is denser?"

EDIT -- Oops, sorry, I missed that they were supposed to be True/False questions. But these two questions can be re-formulated to be T/F as well.

Last edited: Nov 10, 2015
3. Nov 9, 2015

### Staff: Mentor

BTW, my first question works for objects of different sizes, but my second question does not. Can you say why?

4. Nov 9, 2015

### phinds

will an object more dense than water float? (~trick question; depends on shape)

5. Nov 9, 2015

### Staff: Mentor

Ack -- I'm not getting it. PM me a hint?

6. Nov 9, 2015

### phinds

seems obvious, if you take a steel sheet it will sink but form it into a boat and it will float. Do you think that's somehow cheating?

7. Nov 9, 2015

### Staff: Mentor

Depends on your definition of density. Or density, depending on the year...

8. Nov 10, 2015

### Andy Resnick

Here's a couple:
True/false: a (closed) truck carrying 8 tons of canaries weighs less if some of the canaries are flying around.
True/false: oil and water mixtures will behave the same on the space station as they do on the ground.

Some questions from me:
1) What is the age/grade of the students?
2) Why are you asking true/false questions instead of multiple choice questions? Even three options (e.g. 'more', 'less', 'same') will give you more information about concept confusion than 'true/false', which has a 50% correct answer rate when students randomly guess.

9. Nov 10, 2015

### maximus123

The students are 13-14 years. The true or false will be an activity in which the students use small white boards to write on and to hold up the answer to each question. I will then explain why the answer is either true or false. Thanks.

10. Nov 12, 2015

### cpscdave

GAH! Whats the answer to this? It's something I've wondered about before but couldn't find a definitive answer :D

11. Nov 12, 2015

### Staff: Mentor

12. Nov 12, 2015

### Andy Resnick

Here's a few videos:

Don Petit, who started doing these things, is awesome.

13. Nov 16, 2015

### MexChemE

I've always liked this one:

True or false: A flame will always burn upwards.

You could restrict the question to consider the Earth's atmosphere only, or generalize it.

14. Dec 6, 2015

### Mister T

A crown appears to made of gold, but is really made of lead and has a coating of gold. The density of the crown will be greater than the density of gold.

To those who think this question is too simple, try it on your students. You'll be surprised. But the question is good in a situation like this because it launches discussions that lead to better comprehension. Some students will have to be led through a numerical example to be able to understand. Like two unit cubes made of different metals are welded together into a single object with a volume of two units. The density of the composite object has to be directly calculated for students to see that its density lies between the densities of the two metals. Many students, especially at that age, do not have a clear understanding of either mass or volume, so they can't possibly form an understanding of what happens when you form their ratio.

If you really want to pursue this line of pedagogy, try these:

A piece of paper is crumpled up. It's volume decreases.
A piece of paper is crumpled up. It's mass decreases.
A piece of paper is crumpled up. It's density increases.