Why is weight a vector

PhD is earned in a subfield, it doesn't automatically make you bright. For any vector physical quantity it may make perfect sense to define a corresponding scalar quantity equal to that vector's magnitude. Unsurprisingly, both those quantities will usually share a common name.

For example, acceleration is a vector, but 9. Of course, you may call the latter acceleration magnitude if you want to be pedantic, but people who are calling it just acceleration and asserting it's a scalar are not outright wrong. As everyone else has said, this debate is mostly a definitional quibble about exactly how the word "weight" is defined. Two thoughts:. But in colloquial speech there almost no words that are commonly used to indicate both a magnitude and a direction.

That's why the concept of vectors needs to be taught to beginning students - it's not totally intuive. So if you're going by the colloquial rather than the scientific definition of words, then arguably nothing counts a vector. I wouldn't get too hung up on this. The gravitational force exerted on an object is most definitely a vector, but on the surface of the earth, you don't need to make much distinction because for all intents and purposes, it always points in the same direction -- downward.

I suspect the issue may be one of terminology. Yes, if "weight" refers to the force, it is a vector. But your teacher may very well be referring to the magnitude on the force, i. Again, on the surface of the earth, the magnitude conveys essentially the same information as the vector because the direction is known, and you typically don't use the word "weight" in other circumstances.

It is the force a given mass is accelerated towards another mass. Therefore it changes by the location. If you have a rope, you give its strength in Newton most prefer daN, dekanewton because it is almost the same force as 1 kg on normal earth. The same rope holding barely a mass on Earth will snap on Jupiter, but can hold six times the same mass on the moon. So you are right. Yakk's answer is incorrect because the vector component is not neglible.

If you make precise measurements, you will see that mountains or regions with high density changes the direction of the weight, you cannot say anymore it is pointing to the barycenter of the earth.

If weight is not a vector then why is it that there is a position between the Earth and the Moon where your weight is zero. At this point the gravitational attraction on you due to the Moon your weight due to the Moon is equal in magnitude but opposite in direction to the gravitational attraction on you due to the Earth your weight due to the Earth. The subtext of your question - how to deal with an instructor who makes mistakes - however, is harder to answer.

Many people, myself included, don't like admitting their mistakes. I certainly wouldn't recommend, however, being confrontational, questioning their qualifications or work, or making remarks about their age.

If possible, just understand the matter to your satisfaction, then let it go. Mass is a scalar; weight is a vector. Mass does not change regardless of gravitation field, but weight to be precise is the sum of vector components from all gravitation fields that attract an object.

For example, even on the surface of the Earth the Moon exerts some minute vector component that sums with the Earth's to give you the exact weight of an object, which will depend on the magnitude and direction of the vector component directed toward the Moon's center of mass, as well as on the component directed toward the Earth's center of mass.

This becomes even more significant if an object is in space somewhere between the Earth and the Moon. To specify a precise weight, one must consider all the components of the weight vector.

The magnitude and the direction of a weight vector are dependent on its components. If you want to weigh the oceans precisely, you need to specify their tidal positions. However, practically speaking, it's impossible to solve a 3-body Kepler problem exactly. So, in the absence of certainty about the position of each planet exerting gravitational pull on an object, it would be futile to attempt a precise sum of all the vector components contributing to an object's weight.

That and the insignificance of the influence of other planets in the Solar System on an object at the Earth's surface may be one reason that extra-terrestrial vector components of an object's weight usually are ignored. In common usage "weight" is taken to mean only the vector pointing toward the Earth's center of mass.

That may be why some people use the word "weight" as though it were solely a magnitude, like a scalar, because the direction of the weight vector is tacitly assumed, and is left unstated, and insignificant other components of the weight vector are ignored.

I've always defined weight as the magnitude of the force exerted by gravity—the convention knzhou and gogators refer to in the comments. Wikipedia also mentions this convention, citing Halliday, Resnick, and Walker's Fundamentals of Physics 8th ed.

It may not be a coincidence my first few physics courses used this book. I was surprised to learn that this convention isn't the most common one. If you keep studying physics or math, you'll often run into situations where several conflicting definitions of a term coexist, even though you may think one of them is obviously better than the others. For example:.

In special relativity, some people define energy and momentum as the time and space components of the 4-momentum, respectively. Others define energy as the magnitude of the 4-momentum, and momentum as the 4-momentum itself. In differential geometry, some people allow manifolds to have boundaries. Others reserve the term manifold for manifolds without boundaries, using the term manifold with boundary when boundaries are allowed. This isn't really a terminology conflict, but I can't resist mentioning it.

When reading physics or math in French, beware of the false cognate positif. It sounds like it means positive , but it actually means nonnegative! The French term for positive is strictement positif. These conflicts of convention don't cause any problems, as long as everyone is aware that multiple conventions exist, and everyone is careful to say which convention they're using. They probably aren't going away anytime soon, so I recommend getting used to them.

I think we just can follow Wikipedia definition :. In science and engineering, the weight of an object is usually taken to be the force on the object due to gravity.

Weight is a vector whose magnitude a scalar quantity , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g. In colloquial language, weight is often set equal to mass. For example: "My weight is 70 kilogrammes. All weight scales show you a number. Gauged for the earth and standing on the scale on earth this is your mass. But on the moon, the weight scale shows you a different number. This means that what the number the scale shows you is not your mass except on earth but a measure of the force that's acting on you.

So what you actually measure with a scale is the force. So weight is a force, but only on earth, you can see directly your mass while standing on a scale. Gauged for the moon, off course you would see the same mass, but multiplied by the moon's gravitational acceleration which is a vector, and thus weight is one too you'll weigh less than on earth.

Putting an earth gauged scale on the moon, you'll see a smaller number and people are right by saying that you weigh less on the moon, but because weight is confused with mass, many also think their mass is less on the moon.

If "weight" is understood as a force of gravity, then it is a vector, because force is a vector. Mass is the scalar value that can be used to compute the gravity force. I think your professor is mixing up terms. Mass is scalar, weight is a vector. But many people get into the habit of using the terms interchangeably. Also, don't always believe everything someone in a "superior position" tells you. Sometimes they are wrong, so question everything. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object.

Scalar quantities have only a magnitude. When comparing two vector quantities of the same type, you have to compare both the magnitude and the direction. For scalars, you only have to compare the magnitude. When doing any mathematical operation on a vector quantity like adding, subtracting, multiplying.. This makes dealing with vector quantities a little more complicated than scalars. On the slide we list some of the physical quantities discussed in the Beginner's Guide to Aeronautics and group them into either vector or scalar quantities.

Of particular interest, the forces which operate on a flying aircraft, the weight , thrust , and aerodynmaic forces , are all vector quantities. The resulting motion of the aircraft in terms of displacement, velocity, and acceleration are also vector quantities.

These quantities can be determined by application of Newton's laws for vectors. The scalar quantities include most of the thermodynamic state variables involved with the propulsion system, such as the density , pressure , and temperature of the propellants.

The energy , work , and entropy associated with the engines are also scalar quantities. Vectors have magnitude and direction, scalars only have magnitude. The fact that magnitude occurs for both scalars and vectors can lead to some confusion. There are some quantities, like speed , which have very special definitions for scientists.

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