Why does your mass not change on the moon

Today’s Wonder of the Day was inspired by kaily. kaily Wonders, “how much would i weigh on the moon” Thanks for WONDERing with us, kaily!

People first walked on the Moon on July 20, 1969. When Buzz Aldrin and Neil Armstrong stepped out onto the surface of the Moon that day, they not only made world history — they lost weight. How is this possible?

Before we can understand weight, we must first understand gravity and mass. Gravity is a natural force that attracts objects to each other.

On Earth, gravity is the constant force pulling us toward Earth and preventing us from flying off into space like a balloon. When you step on a scale, it shows your weight as a number. This number is actually a measurement of the gravitational pull Earth has on you.

Mass is how much “stuff" you are made of. Unlike weight, your mass is the same whether you are on Earth, on Mars, on the moon, sitting in your living room, swimming in the ocean, or floating somewhere in outer space.

Someone who weighs 200 pounds has more mass than someone who weighs 100 pounds. The more mass a person has, the greater the pull of gravity on them. This is why a scale shows a higher number for a larger person.

Small celestial bodies have weaker gravitational pulls than Earth. Larger planets, such as Jupiter and Saturn, have stronger gravitational pulls, which means you'd weigh more if you visited those planets.

Since the Moon is smaller than Earth, it has a weaker gravitational pull. In fact, the Moon only has 1/6 the gravity that Earth does. This means you weigh six times less on the Moon than you do on Earth!

When the astronauts landed on the Moon in 1969, they wore space suits and carried heavy packs of equipment. Since gravity is much weaker on the Moon, everything weighed only 1/6 of its Earth-weight, and the astronauts were able to move around the Moon very easily.

On planet Earth, we tend to think of the gravitational effect as being the same no matter where we are on the planet. We certainly don’t see variations anywhere near as dramatic as those between the Earth and the Moon. But the truth is, the Earth’s topography is highly variable with mountains, valleys, plains, and deep ocean trenches. As a consequence of this variable topography, the density of Earth’s surface varies. These fluctuations in density cause slight variations in the gravity field, which, remarkably, GRACE can detect from space.

A Closer Look at the Gravity Field

Although the Earth’s surface is not uniform, for the most part, the variations are constant over very long time intervals. In other words, if a mountain was at a given location last month, it’s probably going to be at that same location this month as well, and for all intents and purposes the mass of the mountain is unchanged. This means that the gravity influence of these larger features is pretty much the same over a very long time and is known as the mean (or long-term average) gravity field.

There are other mass variations, however, that occur on much smaller time scales. These are mostly due to variations in water content as it cycles between the atmosphere, oceans, continents, glaciers, and polar ice caps. These shorter-term mass fluctuations contribute to what is known as the time-variable gravity field.

Both the mean gravity field and the monthly maps of the time-variable gravity field are useful tools for scientists as they study the Earth’s changing climate. The mean gravity field helps scientists better understand the structure of the solid Earth and learn about ocean circulation. Likewise, scientists use time-variable gravity to study ground water fluctuations, sea ice, sea level rise, deep ocean currents, ocean bottom pressure, and ocean heat flux.

next: Gravity Anomaly Maps and The Geoid
back: Introduction

This famous photograph of an astronaut taking a “giant leap for mankind” demonstrates the effect of the moon’s lower gravity on a person’s weight. Because the moon is smaller than the Earth and about 60 percent as dense, the astronaut’s weight is only about one-sixth of what it would be on Earth. Although they are not as dramatic as the Earth-moon difference, slight variations in the mass and density across the Earth’s surface do create differences in Earth’s gravity field.

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Would a change in the mass or radius of the moon have any effect on its speed?

When asked this question in an assignment, I stated that it did not. My reasoning being that a change in the mass or radius of the moon would in no way change the acceleration or velocity of the moon. The moon would travel along the same path, the only difference being that the gravitational force being exerted by/on the Earth and Moon would be of a lesser magnitude. As the mass of the Moon decreases by ½, does the gravitational force.

F=ma

½F=½m*a

The original gravitational force being exerted is double that of the new gravitational force

2(G MiMii/r2)=G Mi(1/2Mii)/r2

I got this answer wrong and I am unsure why. Was I wrong in my approach? Are there other forces that I should have taken into account when coming to my conclusion?

Edit:The mass of the moon simply vanishes.