# Category: Weight/mass

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## Weight/mass

The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Definitions of mass often seem circular because it is such a fundamental quantity that it is hard to define in terms of something else.

All mechanical quantities can be defined in terms of mass, length, and time. The usual symbol for mass is m and its SI unit is the kilogram. While the mass is normally considered to be an unchanging property of an object, at speeds approaching the speed of light one must consider the increase in the relativistic mass.

Since the weight is a forceits SI unit is the newton. For an object in free fall, so that gravity is the only force acting on it, then the expression for weight follows from Newton's second law. You might well ask, as many do, "Why do you multiply the mass times the freefall acceleration of gravity when the mass is sitting at rest on the table?

## For the Last Time: The Difference Between Weight and Mass

The value of g allows you to determine the net gravity force if it were in freefall, and that net gravity force is the weight. You can view the weight as a measure of the mass in kg times the intensity of the gravity field, 9. Data can be entered into any of the boxes below. Then click outside the box to update the other quantities.

The kilogram is the SI unit of mass and it is the almost universally used standard mass unit. The associated SI unit of force and weight is the Newton, with 1 kilogram weighing 9. However, in the US common units, the pound is the unit of force and therefore weight. The pound is the widely used unit for commerce. The use of the pound force constrains the mass unit to an inconveniently large measuring unit called a "slug". The use of this unit is discouraged, and the use of exclusively SI units for all scientific work is strongly encouraged. While the actual weight of a person is determined by his mass and the acceleration of gravity, one's "perceived weight" or "effective weight" comes from the fact that he is supported by floor, chair, etc.

If all support is removed suddenly and the person begins to fall freely, he feels suddenly "weightless" - so weightlessness refers to a state of being in free fall in which there is no perceived support. The state of weightlessness can be achieved in several ways, all of which involve significant physical principles.

Mass and Weight The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Index What about the weightless condition?What's the difference between weight and mass? Many people use these terms interchangeably, but that only works because all but a few of us live on Earth.

If we start taking up residence in space colonieson the Moon or on other planets, we'll have to get more precise when we talk about how much stuff is in our stuff. So here's a quick breakdown of weight versus mass:. Mass: If you could count up the number of protons, neutrons, and electrons in an object which you probably can'tthis would be a measure of the mass.

The mass is essentially "how much stuff" is in an object. Yes, I know that's just a partial definition—but it's good enough for now. Common units for mass are the kilogram and the gram. If you insist on using silly imperial units, the unit for mass is the slug true.

Weight: There is a gravitational interaction between objects that have mass. If you consider an object interacting with the Earth, this force is called the weight. The unit for weight is the Newton same as for any other force. OK, fine—the stupid pound is also a unit for weight.

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Most humans on the surface of the Earth can get away with saying either "weight" or "mass" because they are proportional to each other. If you know the mass of something mthen the weight W can be found as:.

In this expression, g is the local gravitational field. The key word here is "local. It doesn't work at least not very well for kilometers above the surface of the Earth and it doesn't work on Mars. Only on the surface of the Earth is there a proportionality constant of 9. Since most humans live on the surface of the Earth, no one really complains about using "weight" and "mass" to basically mean the same thing. So, you want to find the mass of that stack of sticky notes?

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Simple, just put it on a scale and record the reading on the display. Like this. That looks simple, right? It just gives you the mass.During these challenging times, we guarantee we will work tirelessly to support you. We will continue to give you accurate and timely information throughout the crisis, and we will deliver on our mission — to help everyone in the world learn how to do anything — no matter what.

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Thank you to our community and to all of our readers who are working to aid others in this time of crisis, and to all of those who are making personal sacrifices for the good of their communities. We will get through this together. Updated: October 26, References. The weight of an object is the force of gravity exerted on that object. The mass of an object is the amount of matter it has, and it stays the same wherever you are, regardless of gravity. Create an account. We use cookies to make wikiHow great. By using our site, you agree to our cookie policy. As the COVID situation develops, our hearts ache as we think about all the people around the world that are affected by the pandemic Read morebut we are also encouraged by the stories of our readers finding help through our site.

Article Edit. Learn why people trust wikiHow. To create this article, 60 people, some anonymous, worked to edit and improve it over time. Together, they cited 8 references. This article has also been viewedtimes. Learn more Calculating the Weight. Sample Problems.The terms "mass" and "weight" are used interchangeably in ordinary conversation, but the two words don't mean the same thing.

The difference between mass and weight is that mass is the amount of matter in a material, while weight is a measure of how the force of gravity acts upon that mass. For the most part, when comparing mass and weight on Earth—without moving! If you change your location with respect to gravity, mass will remain unchanged, but weight will not. For example, your body's mass is a set value, but your weight is different on the Moon compared with on Earth.

While a person's mass doesn't change elsewhere in the solar system, the acceleration due to gravity and weight varies dramatically. The calculation of gravity on other bodies, as on Earth, depends not just on mass but also on how far the "surface" is from the center of gravity. On Earth, for example, your weight is slightly lower on a mountain top than at sea level.

The effect becomes even more dramatic for large bodies, such as Jupiter. While the gravity exerted by Jupiter due to its mass is times greater than that of Earth, you wouldn't weigh times more because its "surface" or the cloud level we call the surface is so far out from the center. Other celestial bodies have different values of gravity than Earth does.

To get your weight, simply multiply by the appropriate number. For example, a pound person would weigh pounds on Jupiter, or 2. You may be surprised by your weight on other planets. It makes sense that a person would weigh about the same on Venus, because that planet is about the same size and mass as Earth. However, it may seem odd that you'd actually weigh less on the gas giant Uranus. Your weight would be only slightly higher on Saturn or Neptune. Although Mercury is much smaller than Mars, your weight would be about the same. The Sun is much more massive than any other body, yet you'd "only" weigh about 28 times more. Of course, you'd die on the Sun from the massive heat and other radiation, but even if it were cold, the intense gravity on a planet that size would be deadly. Share Flipboard Email. Anne Marie Helmenstine, Ph. Chemistry Expert.If you spend any time interacting with people at work or school and watch any kind of television-style programming, it would be unusual for you to go even a full day without hearing at least one of the words mass or weight.

This is especially true of the latter, given the number of people at any time who are attempting to slim their bodies through some combination of physical activity and dietary modification.

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Finding the mass and weight of objects in the modern world is easy enough: Find a suitably sized scale, put the object on it, and read the digital or analog numbers that result. But calculating mass from weight or conversely can be confusing because these terms are used incorrectly or imprecisely in everyday language.

Mass is one of two fundamental quantities in physics, the other being length. By "fundamental," this means that all other units e. Mass is a measure of "stuff," apart from whatever influence gravity has on that stuff.

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At root level, everything that has mass is made up of electrons, protons and neutrons or if you want to be choosy, subatomic particles. One key property of mass is that gravity does act on it if it is present, resulting in a force called weight.

The value of g on Earth's surface is 9. To find the weight of something, simply multiply its mass by the value of the local gravitational field, and you get a result in newtons N. For example, if your mass is 50 kg about poundsthen your weight is 50 9. The point that must be overwhelmingly emphasized is that weight is a force.

Mass does not require gravity for its own existence, whereas weight does. It is easy to conflate the two because it is rare for anyone on Earth to operate in zero-gravity conditions. For this reason, when you calculate your mass on a scale designed for use on Earth, weight is already factored into the operation of the scale. Mass is not weight, but they are always directly proportional to each other by the value of g, whatever it may be. But what does this mean in terms of imperial pounds and ounces units?

In fact, a unit of mass exists in this scheme, called the slug, but it is ignored today. If someone says she weighs pounds, think of this as her mass, which would be 50 kg in SI units.

Mass and length together give rise to an important variable called density. Volume, which is a measurement of a "chunk" of three-dimensional space, is derived from length units, and in the metric system, it has units of m 3.

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Density is mass divided by volume and offers a sense of the "heaviness" of an object in relation to its size. Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont.

Formerly with ScienceBlogs.Mass, weight and volume are mathematical and scientific quantities used to describe objects in space. Often, the aforementioned terms -- especially mass and weight -- are used interchangeably to mean the same thing, though they mean very different things.

That they are different, however, doesn't mean they aren't directly related. In fact, if you know one of the above two values of an object, you can then calculate the third value using mathematical equations. Mass refers to the amount of matter that an object -- whether liquid, gas or solid -- contains.

It's generally measured in kilograms and grams, and it's a constant quantity that doesn't change, regardless of where an object resides. In particular, an object's mass remains the same whether it's on the moon, on Earth, on Saturday or even if it's just floating through space. In addition, mass is independent of size, meaning that though a bowling ball and soccer ball are about the same size, the bowling bowl has a greater mass.

Weight refers to the pull of gravity on an object. Because gravity changes throughout the solar system from planet to planet, an object weight's doesn't remain constant.

For instance, someone who weighs lbs. This is because gravity and weight are directly related, in that as the force of gravity increases or decreases, so does an object's weight.

Volume refers to the amount of space that an object takes up. Liquid volumes are measured in literals or milliliters; solid volumes are measured in meters cubed or centimeters cubed -- both of which are equal.

To measure a solid object's volume, scientists place the object in a container of water and then measure how many milliliters it displaces. Vivek Saxena has been a full-time freelance writer sincecontributing to several online publications. Prior to becoming a writer, Saxena studied computer technology at Purdue University.

### Mass / Weight Converter

About the Author. Copyright Leaf Group Ltd.In common usage, the mass of an object is often referred to as its weightthough these are in fact different concepts and quantities. In scientific contexts, mass is the amount of " matter " in an object though "matter" may be difficult to definewhereas weight is the force exerted on an object by gravity.

The object's weight is less on Marswhere gravity is weaker, and more on Saturnand very small in space when far from any significant source of gravity, but it always has the same mass.

Objects on the surface of the Earth have weight, although sometimes the weight is difficult to measure. An example is a small object floating in water, which does not appear to have weight since it is buoyed by the water; but it is found to have its usual weight when it is added to water in a container which is entirely supported by and weighed on a scale.

Thus, the "weightless object" floating in water actually transfers its weight to the bottom of the container where the pressure increases. Similarly, a balloon has mass but may appear to have no weight or even negative weight, due to buoyancy in air.

However the weight of the balloon and the gas inside it has merely been transferred to a large area of the Earth's surface, making the weight difficult to measure. The weight of a flying airplane is similarly distributed to the ground, but does not disappear. If the airplane is in level flight, the same weight-force is distributed to the surface of the Earth as when the plane was on the runway, but spread over a larger area.

A better scientific definition of mass is its description as being composed of inertiawhich is the resistance of an object being accelerated when acted on by an external force. Gravitational "weight" is the force created when a mass is acted upon by a gravitational field and the object is not allowed to free-fall, but is supported or retarded by a mechanical force, such as the surface of a planet. Such a force constitutes weight.

While the weight of an object varies in proportion to the strength of the gravitational field, its mass is constant, as long as no energy or matter is added to the object. Mass is among other properties an inertial property; that is, the tendency of an object to remain at constant velocity unless acted upon by an outside force. Inertia is seen when a bowling ball is pushed horizontally on a level, smooth surface, and continues in horizontal motion.

This is quite distinct from its weight, which is the downwards gravitational force of the bowling ball one must counter when holding it off the floor.

The weight of the bowling ball on the Moon would be one-sixth of that on the Earth, although its mass remains unchanged. Consequently, whenever the physics of recoil kinetics mass, velocity, inertia, inelastic and elastic collisions dominate and the influence of gravity is a negligible factor, the behavior of objects remains consistent even where gravity is relatively weak. For instance, billiard balls on a billiard table would scatter and recoil with the same speeds and energies after a break shot on the Moon as on Earth; they would, however, drop into the pockets much more slowly.

In the physical sciences, the terms "mass" and "weight" are rigidly defined as separate measures, as they are different physical properties. In everyday use, as all everyday objects have both mass and weight and one is almost exactly proportional to the other, "weight" often serves to describe both properties, its meaning being dependent upon context.

For example, in retail commerce, the "net weight" of products actually refers to mass, and is expressed in mass units such as grams or ounces see also Pound: Use in commerce. Conversely, the load index rating on automobile tires, which specifies the maximum structural load for a tire in kilograms, refers to weight; that is, the force due to gravity. Before the late 20th century, the distinction between the two was not strictly applied in technical writing, so that expressions such as "molecular weight" for molecular mass are still seen.

Because mass and weight are separate quantities, they have different units of measure.