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**Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?**

« **on:**15/06/2012 13:39:18 »

Going back to basics and the original question

Do we need acceleration to define the concept of mass?

The IPK is made of a platinum–iridium alloy and is stored in a vault at the International Bureau of Weights and Measures in Sèvres, France. It is known as

http://en.wikipedia.org/wiki/Kilogram

The kilogram is by definition what the IPK weighs and is not a constant in the sense that the speed of light is a constant.

Weight

From Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Weight

The Newton

http://en.wikipedia.org/wiki/Newton_(unit)

http://www.wired.com/magazine/2011/09/ff_kilogram/all/1

What is the point of the above? The point is the

As Le Grand K has been loosing weight in comparison to the rest of the Universe it is necessary to find a way of defining mass by using some constant of nature as opposed to using an artifact.

The other approach is to use an apparatus called a watt balance, which compares electrical and mechanical power.

http://www.wired.com/magazine/2011/09/ff_kilogram/all/1

Both of the above alternatives of defining a kg of mass require weighing the object. In the first case knowing the weight of a silicon atom and counting (calculating) the number of atoms. In the second case weighing the object by knowing the amount of energy required to levitate it. Both scenarios require weighing the object and that requires the use of a non-inertial (accelerating) reference frame.

Do we need acceleration to define the concept of mass?

*"The kilogram or kilogramme (SI symbol: kg), also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram (IPK), which is almost exactly equal to the mass of one liter of water."*

The IPK is made of a platinum–iridium alloy and is stored in a vault at the International Bureau of Weights and Measures in Sèvres, France. It is known as

**Le Grand K**.http://en.wikipedia.org/wiki/Kilogram

The kilogram is by definition what the IPK weighs and is not a constant in the sense that the speed of light is a constant.

Weight

From Wikipedia, the free encyclopedia

*"A spring scale measures the weight of an object (according to the operational definition)*

In science and engineering, the weight of an object is the force on the object due to gravity.[2][3] Its 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;[4] thus: W = mg. When considered a vector, weight is often denoted by a bold letter W. The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, about one-sixth as much on the Moon, and very nearly zero when in deep space far away from all bodies imparting gravitational influence."In science and engineering, the weight of an object is the force on the object due to gravity.[2][3] Its 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;[4] thus: W = mg. When considered a vector, weight is often denoted by a bold letter W. The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, about one-sixth as much on the Moon, and very nearly zero when in deep space far away from all bodies imparting gravitational influence."

http://en.wikipedia.org/wiki/Weight

The Newton

*"Definition*

The newton is the SI unit for force; it is equal to the amount of net force required to accelerate a mass of one kilogram at a rate of one metre per second squared. Newton's second law of motion states: F = ma, multiplying m (kg) by a (m/s2), The newton is therefore:[1]

N=kg x m/s

Units used:

N = newton

kg = kilogram

m = metre

s = second

The newton is the SI unit for force; it is equal to the amount of net force required to accelerate a mass of one kilogram at a rate of one metre per second squared. Newton's second law of motion states: F = ma, multiplying m (kg) by a (m/s2), The newton is therefore:[1]

N=kg x m/s

^{2}Units used:

N = newton

kg = kilogram

m = metre

s = second

http://en.wikipedia.org/wiki/Newton_(unit)

*“Le Grand K has been losing weight — or, by the definition of mass under the metric system, the rest of the universe has been getting fatter. The most recent comparison, in 1988, found a discrepancy as large as five-hundredths of a milligram, a bit less than the weight of a dust speck, between Le Grand K and its official underlings.*

This state of affairs is intolerable to the guardians of weights and measures. “Something must be done,” says Terry Quinn, director emeritus of the International Bureau of Weights and Measures, the governing body of the metric system. Since the early 1990s, Quinn has campaigned to redefine the kilogram based not on a physical prototype but on a constant of nature, something hardwired into the circuitry of the universe. In fact, of the seven fundamental metric units — the kilogram, meter, second, ampere, kelvin, mole, and candela — only the kilogram is still dependent on a physical artifact. (The meter, for example, was redefined 30 years ago as the distance traveled by light in a given fraction of a second.)”This state of affairs is intolerable to the guardians of weights and measures. “Something must be done,” says Terry Quinn, director emeritus of the International Bureau of Weights and Measures, the governing body of the metric system. Since the early 1990s, Quinn has campaigned to redefine the kilogram based not on a physical prototype but on a constant of nature, something hardwired into the circuitry of the universe. In fact, of the seven fundamental metric units — the kilogram, meter, second, ampere, kelvin, mole, and candela — only the kilogram is still dependent on a physical artifact. (The meter, for example, was redefined 30 years ago as the distance traveled by light in a given fraction of a second.)”

http://www.wired.com/magazine/2011/09/ff_kilogram/all/1

What is the point of the above? The point is the

*"The kilogram or kilogramme (SI symbol: kg), also known as the kilo, is the base unit of mass in the International System of Units”*is defined by measuring its acceleration (weighing it).*“Its 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;[4] thus: W = mg.” “ The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton.” “The newton is the SI unit for force; it is equal to the amount of net force required to accelerate a mass of one kilogram at a rate of one metre per second squared.” “In science and engineering, the weight of an object is the force on the object due to gravity.[2][3] Its 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;[4] thus: W = mg.”*So, going back to the original question “Do we need acceleration to define the concept of mass?” From the above it is obvious that we do.As Le Grand K has been loosing weight in comparison to the rest of the Universe it is necessary to find a way of defining mass by using some constant of nature as opposed to using an artifact.

*“So two decades ago, as Quinn’s campaign to switch the kilo to a physical constant began to gain traction, Becker and his colleagues decided to tackle the problem from the opposite direction. Building upon their earlier work, they decided to create a 1-kilogram sphere, not from hydrogen, but from silicon. The sphere would be identical in mass to the international prototype. Then, because Becker’s x-ray experiments had shown that the atoms were arranged in a regular pattern, they could use basic geometry to deduce how many silicon atoms the crystalline sphere contained. Once the number of atoms was determined with sufficient precision, that figure would forever define the mass of the kilogram. In other words, they set out to make a new artifact superior to Le Grand K — but only so that they could count its atoms and then eliminate all kilogram artifacts in perpetuity.”*The other approach is to use an apparatus called a watt balance, which compares electrical and mechanical power.

*“On the upper floor is a room-sized scale dominated by a wheel fabricated of milled aluminum. Below the wheel is a hand-sized pan supporting a platinum-iridium mass positioned like an apple on a produce scale. One floor below, superconducting electromagnets counteract the downward tug of the platinum-iridium. In other words, the gravitational force on the mass is balanced with the electrical force produced by current in the copper coil. Once calibrated against the international prototype, the electronic kilogram can be defined in terms of the voltage required to levitate Le Grand K — a numerical value, governed by a natural constant, that can be used to calibrate any future watt balance — and the international prototype can at last be sent into retirement.”*http://www.wired.com/magazine/2011/09/ff_kilogram/all/1

Both of the above alternatives of defining a kg of mass require weighing the object. In the first case knowing the weight of a silicon atom and counting (calculating) the number of atoms. In the second case weighing the object by knowing the amount of energy required to levitate it. Both scenarios require weighing the object and that requires the use of a non-inertial (accelerating) reference frame.