M1: Does a scale measure weight or mass?

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    I know that weight is the force of an object acting on it due to gravity; so unless the scale is in a room with vacuum and no gravity a scale on earth provides the weight and not the mass as many would say. Can explain to me if this is right or not?
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    (Original post by tryingtomaths)
    I know that weight is the force of an object acting on it due to gravity; so unless the scale is in a room with vacuum and no gravity a scale on earth provides the weight and not the mass as many would say. Can explain to me if this is right or not?
    It measures weight, but gives readings of mass as the unit is the kg.
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    (Original post by tryingtomaths)
    I know that weight is the force of an object acting on it due to gravity; so unless the scale is in a room with vacuum and no gravity a scale on earth provides the weight and not the mass as many would say. Can explain to me if this is right or not?
    You are right. A scale (or any other object) responds to a force acting on it, and the force in this case is the weight of the object sitting on it.

    However, your comment about a "room with vacuum" is meaningless; vacuums don't affect the force of gravity; and if there were no gravity, there would be no weight.
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    (Original post by atsruser)
    You are right. A scale (or any other object) responds to a force acting on it, and the force in this case is the weight of the object sitting on it.

    However, your comment about a "room with vacuum" is meaningless; vacuums don't affect the force of gravity; and if there were no gravity, there would be no weight.
    oh yes; sorry about that; but i still don't understand why do we say that a balance gives us mass when infact it gives us weight because the force of gravity is acting on us? i would be thankful if you can clarify
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    (Original post by tryingtomaths)
    oh yes; sorry about that; but i still don't understand why do we say that a balance gives us mass when infact it gives us weight because the force of gravity is acting on us? i would be thankful if you can clarify
    Scales actually measure force in N but provide an approximation for the mass of the object paced upon them.
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    (Original post by tryingtomaths)
    I know that weight is the force of an object acting on it due to gravity; so unless the scale is in a room with vacuum and no gravity a scale on earth provides the weight and not the mass as many would say. Can explain to me if this is right or not?
    It actually measures the force of your feet pushing on the scales (but gives you a reading in kg because that's what people understand). Jumping up and down on it affects the reading because that changes the force between your feet and the scales. If you stay still the force between your feet and the scales equals your weight.

    Try an experiment. Take the scales to a lift that has a noticeable acceleration. This will affect the force between your feet and the scales and your "weight" will apparently have changed.

    This is an easier experiment to carry out than standing on scales on the moon.
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    (Original post by tryingtomaths)
    oh yes; sorry about that; but i still don't understand why do we say that a balance gives us mass when infact it gives us weight because the force of gravity is acting on us? i would be thankful if you can clarify
    1. When you stand on a set of scales, your weight (the force produced on your body by the gravitational attraction of the Earth) compresses the springs in the scales by a certain amount l which is proportional to your weight, W.

    2. When the springs are compressed, they turn a pointer on a scale.

    2. Your weight on Earth can be calculated by W_E=mg_E where m is your mass, and g_E is the size of the acceleration, on Earth, of any body with mass.

    3. The numbers on the scale give a reading in kilograms, which is a measure of mass. The numbers are calibrated assuming that you calculate your weight as above i.e. that the scales are being used on the surface of the Earth.

    4. If you took the scales to the moon, then your weight would be calculated by W_m=mg_m where m is your mass, and g_m is the size of the acceleration, on the moon, of any body with mass.

    5. Moon gravity is weaker than Earth gravity so g_m < g_E \Rightarrow W_m = mg_m < mg_E = W_E i.e. your weight on the moon is less than your weight on the Earth, even though your mass hasn't changed.

    6. So if you stood on the scales on the moon, they would feel your moon weight, and the springs would be compressed by a smaller amount than that produced by your Earth weight. Hence the reading on the scale would indicate that you have a smaller mass than is actually the case - this is due to the fact that the weight-mass correspondence on the scale assumes that the scales are being used on the Earth.

    Does that help?
 
 
 
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