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Does everyone learn the same gravity in school or is it different everywhere?

So, I learned in physics class at school in the UK that the value of acceleration due to gravity is a constant called g and that it was 9.81m/s^2. I knew that this value is not a true constant as it is affected by terrain and location. However I didn’t know that it can be so significantly different as to be 9.776 m/s^2 in Kuala Lumpur for example. I’m wondering if a different value is told to children in school that is locally relevant for them? Or do we all use the value I learned?

Candelestine ,

I also learned 9.8.

This reminds me of the story of magnetic detonators for torpedos they tried to use in the early days of WW2. They detect the slight disturbance in the Earth’s magnetic field caused by a gigantic hunk of floating metal, and that triggers the detonation.

However, they did not yet know that the Earth’s magnetic field is not consistent over the whole planet, so while they calibrated it to the local field, it functioned very badly in other regions with different field strengths. Torpedo would either detonate far too early, doing minimal damage, or not detonate at all, just hitting the target ship with a loud thunk.

This was largely responsible for the ineffectiveness of American submarines in the early days of our WW2 involvement. Took us a couple years to sort too.

It was called the Mk 42 in case anyone wanted to read a little more. It’s an amusing story. They never wanted to actually properly test them, because they were so damn expensive. So they just didn’t. lol It wasn’t until enough sailors complained and got a high ranking admiral on their side that it got sorted.

rowinxavier ,

People learned different values for g for a number of reasons, but as far as I understand local variability is not one of them. The primary root cause seems to be accuracy of the measurement over time and the age of textbooks/course material.

Over time we have gotten better at measuring the true value of g through advances in technology and this has caused the taught value to shift a little. The value when initially measured had fairly large error margins, meaning that we were sure it was near a specific value but not sure of the exact value. As the tools improved we have reduced the uncertainty, getting to a more accurate and also more precise value, meaning more digits after the decimal as well as higher confidence in each digit. We have also changed what we mean by g over time, bringing it in line with the metric system and basing it on fundamental values and constants. From my understanding the most recent method relies on how much the repulsive force of an electromagnet with a specific number of culombs passing through is overcome by gravity at a specific distance from the center of the mass of Earth, so a little more removed from backyard science than measuring if things drop at the same speed at the top of a mountain and sea level.

Part 2 is the differences in how recent your material is. In my primary school in a relatively affluent area of an affluent country we had textbooks from the last 10 years. My partner went to a school in the same country but a worse area about 5km away from mine. Their school had textbooks literally 20 years old. In that time the measurements had changed, understandings had changed, and they were therefore taught things that were untrue. These sorts of differences based on geography reproduce the impacts of racism and inequality from the past into the future.

RedWeasel ,

While I don’t know the answer and that for simplicity it should probably be a global average, it is probably some “constant“ measured from some location in either Europe or North America before they were able to measure globally using satellites.

pixxelkick ,

It’s at sea level :)

RedWeasel ,

Which sea? The Indian ocean if I recall correctly has a very low gravity value.

JackGreenEarth ,

I just learned ‘about 9.8’ which is true anywhere in the world.

TehWorld ,

Yeah. 9.8 is what I learned. I was generally aware that locality made a difference, but I had no idea that there was that much of a spread. For anything not involving millions of dollars of rocketry and actual satellites a simplified number is likely good enough. Much like Pi, where a couple digits is good enough for most everything and calculating out past 6 digits or so is infinitesimally small.

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