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1. Question:
On the Moon, the force of gravity on an object is only about one-sixth of its value on Earth. Decide whether each of the following would give an accurate measurement if used on the Moon

a) A beam balance like the one in the diagram at the top of the page

b) A balance like the one in the photograph above. (please note the balance the question refers to is a modern type of balance- electronic one)

My understanding is that a beam balance compares weight and on the moon the weight of the object changes not the mass. Since a beam balance compares weight, on the moon if an object's weight changes thus it will not be able to give the accurate reading for mass.
Therefore for (a) i said no it will not give a accurate reading for mass

However, for (b) i said yes it will give an accurate reading of mass because according to the notes i am reading from the modern type of balance detects gravitational pull but gives the reading in units of mass.

The book answers states that (a) gives a more accurate reading of mass
(b) does not

Please can someone help me understand why?

thank you

beam balance

modern balance
Attached Images

2. The way you use a beam balance is to put the object you want to know the mass of into one pan and then you add known masses from a set of masses onto the other pan until the beam is horizontal - at which point you know the masses on both sides are equal.

the gravitational field strength will be equal on both the pans - so the force per mass will be the same on the contents of both pans and it doesn't matter what the value of force per mass actually is, provided it's equal (and also not zero) on both pans it'll work accurately.

The spring balance measures the force on the pan by measuring the compression of a spring - if the force per mass varies the readings won't be accurate.
3. It's testing your fundamental understanding of the differences between gravity and mass.
4. (Original post by Joinedup)
The way you use a beam balance is to put the object you want to know the mass of into one pan and then you add known masses from a set of masses onto the other pan until the beam is horizontal - at which point you know the masses on both sides are equal.

the gravitational field strength will be equal on both the pans - so the force per mass will be the same on the contents of both pans and it doesn't matter what the value of force per mass actually is, provided it's equal (and also not zero) on both pans it'll work accurately.

The spring balance measures the force on the pan by measuring the compression of a spring - if the force per mass varies the readings won't be accurate.
But couldn't you theoretically use the reading you get on the modern scale to work backwards?
5. (Original post by cbreef)
But couldn't you theoretically use the reading you get on the modern scale to work backwards?
Yeah you could correct it by having different dials for different levels of gravity or something similar.

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