Originally posted by Sweden View Post Dear all, This may seem like a stupid question but in conversion of different units between metric and imperial and back again for lots of different properties such as mass, weight, strength, pressure, etc.
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: 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 Mass and kg.
Because mass and weight are separate quantities, they have different units of measure. In the International System of Units SIthe kilogram is the basic unit of mass, and the newton is the basic unit of force.
The non-SI kilogram-force is also a unit of force typically used in the measure of weight. Similarly, the avoirdupois poundused in both the Imperial system and U.
Converting units of mass to equivalent forces on Earth[ edit ] Gravity anomalies covering the Southern Ocean are shown here in false-color relief. This image has been normalized to remove variation due to differences in latitude.
The General Conference on Weights and Measures fixed the value of standard gravity at precisely 9. Thus the kilogram-force is defined as precisely 9.
In reality, gravitational acceleration symbol: Engineers and scientists understand the distinctions between mass, force, and weight. Engineers in disciplines involving weight loading force on a structure due to gravitysuch as structural engineeringconvert the mass of objects like concrete and automobiles expressed in kilograms to a force in newtons by multiplying by some factor around 9.
Material properties like elastic modulus are measured and published in terms of the newton and pascal a unit of pressure related to the newton.
Buoyancy and weight[ edit ] Regardless of the fluid in which an object is immersed gas or liquidthe buoyant force on an object is equal to the weight of the fluid it displaces. A hot air balloon when it has neutral buoyancy has no weight for the men to support but still retains great inertia due to its mass.
Usually, the relationship between mass and weight on Earth is highly proportional; objects that are a hundred times more massive than a one-liter bottle of soda almost always weigh a hundred times more—approximately 1, newtons, which is the weight one would expect on Earth from an object with a mass slightly greater than kilograms.
A common helium-filled toy balloon is something familiar to many. When such a balloon is fully filled with helium, it has buoyancy —a force that opposes gravity.
When a toy balloon becomes partially deflated, it will often become neutrally buoyant and can float about the house a meter or two off the floor.
Though the rubber comprising the balloon has a mass of only a few grams, which might be almost unnoticeable, the rubber still retains all its mass when inflated.
If one were however to weigh a small wading pool that someone then entered and began floating in, they would find that the full weight of the person was being borne by the pool and, ultimately, the scale underneath the pool. However, as noted, an object supported by a fluid is fundamentally no different from an object supported by a sling or cable—the weight has merely been transferred to another location, not made to disappear.
The mass of "weightless" neutrally buoyant balloons can be better appreciated with much larger hot air balloons.
If this fluid is air, the force may be small. Buoyancy effects of air on measurement[ edit ] Normally, the effect of air buoyancy on objects of normal density is too small to be of any consequence in day-to-day activities.
For convenience, a standard value of buoyancy relative to stainless steel was developed for metrology work and this results in the term "conventional mass".
Since objects with precisely the same mass but with different densities displace different volumes and therefore have different buoyancies and weights, any object measured on this scale compared to a stainless steel mass standard has its conventional mass measured; that is, its true mass minus an unknown degree of buoyancy.
In high-accuracy work, the volume of the article can be measured to mathematically null the effect of buoyancy. Types of scales and what they measure[ edit ] A balance-type weighing scale:The kilogram (abbreviation, kg) is the Standard International System of Units unit of alphabetnyc.com is defined as the mass of a particular international prototype made of platinum-iridium and kept at the International Bureau of Weights and Measures.
(a) The mass of a hydrogen molecule (H2) is kg. The sun's average surface temperature is K. Calculate the average speed of a hydrogen molecule at the Sun's surface.
Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). Online calculator to convert pounds to kilograms (lb to kg) with formulas, examples, and tables. Our conversions provide a quick and easy way to convert between Weight or Mass units.
Convert pounds to kg - Weight / Mass Conversions. The kilogram or kilogramme (symbol: kg) is the base unit of mass in the International System of Units (SI), and is defined as being equal to the mass of the International Prototype of the Kilogram (IPK, also known as "Le Grand K" or "Big K"), a cylinder of platinum-iridium alloy stored by the International Bureau of Weights and Measures at Saint-Cloud, France.
Mass is the property which reflects the quantity of matter within a sample. Mass usually is reported in grams (g) and kilograms (kg).. Mass may also be considered to be the property of matter that gives it a tendency to resist acceleration.