Which weighs more?

I have been asking this question to my six-year-old from time for months and get the rocks every time. Then I go through the explanation about why they are the same and she acts like she understands. But when I ask again in a few days I get the rocks again.

The same thing happened with her older brother and sister as well. I'm not sure at what time the brain develops to grasp the right answer to this question, but I speculate around 8. Another very difficult concept is the difference between a city, state, and country.

Quote: Wizard

I have been asking this question to my six-year-old from time for months and get the rocks every time. Then I go through the explanation about why they are the same and she acts like she understands. But when I ask again in a few days I get the rocks again.

What do you mean by "weight"?

The word has two mentings. One is the mass of an object, the other is the force that mass exerts under a gravitational field.

Here, suppose you take a balance and put feathers on one plate and rocks on the other. If they balance, then the gravitational field is irrelevant, right? The balance would hold at equilibrium under different gravitational fields. Say on the Moon's surface, or on Jupiter's, or even inside a constantly accelerating spaceship. So what the balance measures is the amount of matter contained in a discrete object, or its mass.

Now take a bathroom scale. Most of these have a spring which bends or compresses under a force, and thus determines the intensity of said force. This measures weight. On Earth it would report one pound of weight per pound of mass, but on the Moon it would report 1/6 of a pound of weight per pound of mass. For a scale the gravitational field matters.

Now let's salk about pressure. Take one pound each of feathers and rocks and put them in a bag with handles. Pick one up, then the other one. regardless of the fact that both bags hold the same mass, and that those masses exrt the same weight, as the rocks occupy a smaller volume, they exert more pressure on the bag, and therefore on the abg's handles. In other words, the bag with the rocks will feel heavier.

That's part of what makes it so hard to understand. It's not easily proven by experiment.

Quote: Wizard

I have been asking this question to my six-year-old from time for months and get the rocks every time. Then I go through the explanation about why they are the same and she acts like she understands. But when I ask again in a few days I get the rocks again.

The same thing happened with her older brother and sister as well. I'm not sure at what time the brain develops to grasp the right answer to this question, but I speculate around 8. Another very difficult concept is the difference between a city, state, and country.

In this question, "weight" is the measure of the Earth's gravitational pull on the feathers and the rocks. The feathers take up much mores space than the rocks, so their, "center of mass" will be further from the Earth's "center of mass". Since the gravitational pull grows weaker with increasing distance between objects, the Earth's attraction will be weaker on the feathers vs. the rocks. Therefore, the feathers "weigh" less, and the rocks "weigh" more... Or, not.

Quote: Wizard

I have been asking this question to my six-year-old from time for months and get the rocks every time. Then I go through the explanation about why they are the same and she acts like she understands. But when I ask again in a few days I get the rocks again.

Let's see, a pound of (uncompressed) feathers will fall slower than a 1lb rock.

A pound of compressed feathers might be as painful as a rock to be hit in the head with.

And I'm not sure, but possilbly a pound of feathers compressed or not might float better than a rock. Except pumice, which can float. But not sure if 1lb of pumice will float.

Quote: Wizard

I have been asking this question to my six-year-old from time for months and get the rocks every time. Then I go through the explanation about why they are the same and she acts like she understands. But when I ask again in a few days I get the rocks again.

The same thing happened with her older brother and sister as well. I'm not sure at what time the brain develops to grasp the right answer to this question, but I speculate around 8. Another very difficult concept is the difference between a city, state, and country.

Perhaps an experiential object lesson with a balance and actual objects would help cement the concept. Kids organize their worlds according to personal set of traits that they have experienced (things that are light vs. things that are heavy; hot vs. cold; smooth vs. rough, etc.). You can expand her mind by demonstrating that some traits (weight) can have the same value, even when other characteristics are different. However, the breakthrough will happen when she learns how to compare different objects according to a standard scale (Which has more things in it, a carton of eggs or a 12 pack of soda?). She should be learning to add, subtract, and group now, so it will click soon.

Quote: rxwine

And I'm not sure, but possilbly a pound of feathers compressed or not might float better than a rock. Except pumice, which can float. But not sure if 1lb of pumice will float.

Very small rocks!

This remidns me of the trivia question to stump little chidlren: "What color was Napoleon's white horse'"

For some reason a lot of children claim not to have any idea.

In my day, the riddle involved a ton of bricks and feathers.

The key boing that a "ton" is sometimes used to describe a "large pile". That said, I find it interesting that the kids miss the point when comparing pounds.

Then again, Who is buried in Grant's tomb?

Quote: DJTeddyBear

Who is buried in Grant's tomb?

some people claim the answer is "nobody" since correct English would be "Who is entombed in Grant's tomb?" Use of the word "bury" and its derivatives should be restricted to graves.