Is The Earth Getting Heavier?

Classical Mechanics Level 1

Suppose, earth's current mass is $M$ .

According to UNICEF , approximately 353,000 babies are born each day. An average newborn baby has a mass of 5.5 pounds,

After exactly a week from now, the combined mass of the earth will:

Assume that you can neglect any other side-effects (like Space Exploration, asteroids hitting earth, etc) safely.

Increase Decrease Remain the same Decrease, but then will increase

2 solutions

Muhammad Arifur Rahman
Jul 27, 2016

A new baby is born. Where he/she was previously? In the mother's womb, obviously. The most valuable extracts from her/his mother's food kept building up that cute body, gradually. And the food might came from meat, vegetables, herbs etc. the mom took during that period.

So now, did anything went off the earth? Or did the baby come from the outer space?

Actually, the mass is just getting transferred from here to there, within the earth - from the plants to the womb, to the child's tender body.

Ultimately, the birth of a baby doesn't increase the mass of this planet at all.

Thus, earth's mass is conserved!

@Calvin Sir, is Biology the appropiate category for this problem?

Muhammad Arifur Rahman - 4 years, 10 months ago

Yes, i think biology is a more suitable topic

Ashish Menon - 4 years, 10 months ago

I actually answered that it would decrease, because of all the energy and mass which gets lost in space (heat and atmospherical molecules), but I guess it gets fully compensated by the energy the Earth gets from stars? The question seemed rather banal, since Lavoisier's law is something pretty much anyone knows, that's why I tried to see it from another point of view

Cristian Bredford - 4 years, 10 months ago

Actually, this problem is inspired from the Q & A session of Bangladesh Science Olympiad where a 7th grader girl asked this question. And as only a few students learn Lavoisier's Law before 9th grade, its essential to introduce them with this law & apply this to resolve a trivial problem. This would make this law more understandable to them in the future.

Muhammad Arifur Rahman - 4 years, 10 months ago

Ya but the earth gets hit by meteors all the time...

Spencer Parker - 4 years, 10 months ago

You were necessarily instructed to neglect those effects in the problem statement.

Muhammad Arifur Rahman - 4 years, 10 months ago

Nice question, can you please add an assumption that the baby does not get heavy in the time peruod mention. Thanks! :)

Ashish Menon - 4 years, 10 months ago

@Ashish Menon – Is there any problem if the baby gets nourished? Because what he/she eats comes from something that of earth somehow, right? So no matter the baby grows or not, the combined mass is still a constant, isn't it?

Muhammad Arifur Rahman - 4 years, 10 months ago

@Muhammad Arifur Rahman – Wow, now thats some nice logic hats off. Thanks for explaining :)

Ashish Menon - 4 years, 10 months ago

@Ashish Menon – I thought this is a masterpiece of conceptual problems.

Muhammad Arifur Rahman - 4 years, 10 months ago

How would you account for the energy transfer by insolation? If the sun wasn't around to provide light and energy for plants, there would be no vegetables, meat, etc. So there has to be an addition to earth's mass.

Phil Watson - 4 years, 10 months ago

@Phil Watson: Its only the energy that comes from the sun, not mass. The veggies were all in our earth since the birth of the earth, in the form of $N_2, C, O_2$ molecules (or atoms, preliminarily).

Muhammad Arifur Rahman - 4 years, 10 months ago

Lev Grunin
Aug 29, 2016

If earth's mass did change, our orbit would change.

Actually? $T^2=\frac{4\pi^2 r^3}{GM_{sun}}$ Kepler's Law clearly says the orbit depends on the mass of the one at the center, the sun. It doesn't depend on earth's mass at all.

Muhammad Arifur Rahman - 4 years, 3 months ago

Is The Earth Getting Heavier?

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