Activity 16

Read the following text and circle true or false (T / F) to state if the sentences given are true or false.

In practical or everyday applications, we give to weight the same meaning as we gave to mass in physics. In modern scientific usage, however, weight and mass are fundamentally different quantities: mass is an intrinsic property of matter, whereas weight is a force that results from the action of gravity on matter: it measures how strongly gravity pulls on that matter.

However, the recognition of this difference is historically a relatively recent development and in many everyday situations the word "weight" continues to be used when, strictly, "mass" is meant. For example, most people would say that an object "weighs one kilogram", even though the kilogram is a unit of mass.

The distinction between mass and weight is unimportant for many practical purposes because the strength of gravity is very similar everywhere on the surface of the Earth. In such a constant gravitational field, the gravitational force exerted on an object (its weight) is directly proportional to its mass. For example, object “A” weighs 10 times as much as object “B”, so therefore the mass of object “A” is 10 times greater than that of object “B”.

The difference between mass and weight is apparent when, for example objects are compared in different gravitational fields. For example, on the surface of the Moon, gravity is only about one-sixth as strong as on the surface of the Earth. A one-kilogram mass is still a one-kilogram mass (as mass is an intrinsic property of the object) but the downward force due to gravity is only one-sixth of what the object would experience on Earth. So the weight of the object on the moon will be one-sixth of what it would have on Earth.

To convert between weight (force) and mass, Newton's second law of "force = mass °— acceleration" (F = m·a) is used. Here, “F” is the force (weight) due to gravity, “m” is the mass of the object in question, and “a” is the acceleration due to gravity, on Earth approximately 9,81 m/s2. For example, a mass of 2 kg experiences a weight force of 2 kg °— 9,81 m/s2 = 19,62 N.

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