In the above equation, m is mass, ρ is density, and V is volume. While mass is defined by F = ma, in situations where density and volume of the object are known, mass is also commonly calculated using the following equation, as in the calculator provided: In cases where objects undergo acceleration through other forces (such as a centrifuge), weight is determined by multiplying the object's mass by the total acceleration away from free fall (known as proper acceleration). It is important to note that regardless of how strong a gravitational field may be, an object that is in free fall is weightless. On earth, this value is approximately 9.8 m/s 2. In the metric system, weight is measured in Newtons following the equation W = mg, where W is weight, m is mass, and g is the acceleration due to the gravitational field. In circumstances where the gravitational field is constant, the weight of an object is proportional to its mass, and there is no issue with using the same units to express both. In the equation above, F is force, G is the gravitational constant, m 1 and m 2 are the mass of the moon and the object it is acting upon, and r is the moon's radius. This is in accordance with the equation: F = Their mass, however, would still be 70 kg on the moon. ![]() This means that a person with a mass of 70 kg on earth would weigh approximately one-sixth of their weight on earth while on the moon. The force of gravity on the moon, for example, is approximately one-sixth that on earth, due to its smaller mass. Weight, on the other hand, changes based on gravity, as it is a measure of an object's resistance to its natural state of freefall. The mass of an object remains constant regardless of where the object is and is, therefore, an intrinsic property of an object. The words mass and weight are frequently used interchangeably, but even though mass is often expressed by measuring the weight of an object using a spring scale, they are not equivalent. While these are conceptually distinct, there have not been conclusive, unambiguous experiments that have demonstrated significant differences between gravitational and inertial mass. Active gravitational mass is the measure of how much gravitational force an object exerts, while passive gravitational mass is the measure of the gravitational force exerted on an object within a known gravitational field. There exist other common definitions of mass including active gravitational mass and passive gravitational mass. While many different units are used to describe mass throughout the world, the standard unit of mass under the International System of Units (SI) is the kilogram (kg). An inflated balloon, for example, would have significantly less mass than a golf ball made of silver. The amount of mass that an object has is often correlated with its size, but objects with larger volumes do not always have more mass. In classical physics, matter is any substance that has mass and volume. Matter, however, is somewhat loosely defined in science, and cannot be precisely measured. It is most commonly measured as inertial mass, involving an object's resistance to acceleration given some net force. Try mixing oil and water and see how they separate into layers, with the less dense oil on top.Mass is typically defined as the amount of matter within an object. When you mix two or more substances, the most dense substance sinks to the bottom, whilst the least dense substance is more buoyant and floats to the top. This is why you should never comment on your Auntie Mabel's sponge cake by describing it as dense: she was probably going for something a little more airy.ĭensity is also what makes things float or sink. A pound of feathers is filled with airy space, so it's not very dense at all, while a pound of lead feels much more solid, so it's more dense. For an equal amount of space it takes up (volume), lead weighs much more than the feathers (mass).ĭensity can also be thought of as how compacted or compressed a substance is. ![]() So if the question was, 'Which weighs more: a 500ml jug full of feathers or a 500ml jug full of lead?' then the answer would be the lead. ![]() What is density?ĭensity is the mass per volume - not just the straight-up mass. Read on to find out exactly what density is, how it works, and how to calculate density. Although the feathers and the lead both weigh exactly the same (um, a pound), their density is wildly different, and we can sometimes mentally conflate weight and density - even though they're different concepts. ![]() If you've ever been fooled by the old question, ' Which weighs more: a pound of feathers or a pound of lead?' then you wouldn't be alone. To calculate density: p = m/V To calculate mass: m = pV To calculate volume: V = m/p
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