# M1 quick Scale pan questionWatch

#1

For questions like the one shown above, I don't really understand the weight force. So the weight of the the scale pan is 0.5g, but we also include the weight of the brick which is 1.5g when we are looking at the forces acting on the scale pan alone. So is the weight of the brick being exerted onto the scale pan or am I wording this wrong??
Last edited by dont know it; 1 week ago
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1 week ago
#2
(Original post by dont know it)

For questions like the one shown above, I don't really understand the weight force. So the weight of the the scale pan is 0.5g, but we also include the weight of the brick which is 1.5g when we are looking at the forces acting on the scale pan alone. So is the weight of the brick being exerted onto the scale pan or am I wording this wrong??
For part a), you care about forces acting on the scale pan. It doesn't really matter what's inside the scale pan - all the scale pan "knows" is that it is being pulled down by a weight = (1.5+0.5)g and is being pulled up by tension in the rope.

If you think about any object in Mechanics, the atoms contained in it all have mass and there are lots of forces going on inside but we don't care about them, all we care about is the total mass/weight of the object.

Then in b) you have to then consider forces acting on the brick since that's mentioned in the question.
Last edited by Notnek; 1 week ago
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#3
(Original post by Notnek)
For part a), you care about forces acting on the scale pan. It doesn't really matter what's inside the scale pan - all the scale pan "knows" is that it is being pulled down by a weight = (1.5+0.5)g and is being pulled up by tension in the rope.

If you think about any object in Mechanics, the atoms contained in it all have mass and there are lots of forces going on inside but we don't are about them, all we care about is the total mass/weight of the object.

Then in b) you have to then consider forces acting on the brick since that's mentioned in the question.
I'm still confused tbh. The weight of the scale pan is 0.5g, so where's the other 1.5g coming from? Essentially, I'm confused about the weight of the brick. Is its weight being exerted against the scale pan? Because otherwise how can you add the two weights together as the force acting down on the scale pan.
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1 week ago
#4
(Original post by dont know it)
I'm still confused tbh. The weight of the scale pan is 0.5g, so where's the other 1.5g coming from? Essentially, I'm confused about the weight of the brick. Is its weight being exerted against the scale pan? Because otherwise how can you add the two weights together as the force acting down on the scale pan.
Imagine that the brick was glued down to the scale pan and you couldn't see inside the scale pan. Then if you lifted it, it would just feel like something that has mass 2kg and you wouldn't know/care that there's anything inside.

Think about what the difference is between a scale pan with mass 2kg and a scale pan that has mass 0.5kg and contains a 1.5kg brick. In terms of forces acting on both scale pans, there is no difference. They are both being pulled down by the Earth with a force of 2gN and they would both feel the same if you picked them up.

There are forces occurring inside the scale pan that contains the brick but these are irrelevant if all you care about is the scale pan.
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#5
(Original post by Notnek)
Imagine that the brick was glued down to the scale pan and you couldn't see inside the scale pan. Then if you lifted it, it would just feel like something that has mass 2kg and you wouldn't know/care that there's anything inside.

Think about what the difference is between a scale pan with mass 2kg and a scale pan that has mass 0.5kg and contains a 1.5kg brick. In terms of forces acting on both scale pans, there is no difference. They are both being pulled down by the Earth with a force of 2gN and they would both feel the same if you picked them up.

There are forces occurring inside the scale pan that contains the brick but these are irrelevant if all you care about is the scale pan.
Oh I see thanks.
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#6
(Original post by Notnek)
Imagine that the brick was glued down to the scale pan and you couldn't see inside the scale pan. Then if you lifted it, it would just feel like something that has mass 2kg and you wouldn't know/care that there's anything inside.

Think about what the difference is between a scale pan with mass 2kg and a scale pan that has mass 0.5kg and contains a 1.5kg brick. In terms of forces acting on both scale pans, there is no difference. They are both being pulled down by the Earth with a force of 2gN and they would both feel the same if you picked them up.

There are forces occurring inside the scale pan that contains the brick but these are irrelevant if all you care about is the scale pan.
Actually 1 more question . What would you call the force acting downwards on the scale pan when you factor in the forces from the brick? Or do we not know?
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1 week ago
#7
(Original post by dont know it)
Actually 1 more question . What would you call the force acting downwards on the scale pan when you factor in the forces from the brick? Or do we not know?
I'm not completely sure what you mean but your working could look like this:

Treat the scale pan / brick as one 2kg mass.
So the weight of this combined mass is 2gN.
Last edited by Notnek; 1 week ago
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#8
(Original post by Notnek)
I'm not completely sure what you mean but your working could look like this:

Treat the scale pan / brick as one mass with mass 2kg.
So the weight of this combined mass is 2gN.
Yeah I reckon that answers my question. I meant it in a sense like how we would say the weight of the scale pan is 0.5g, but in this case we can't give an object. So instead we call the downward force the weight of the combined mass rather than the weight of a specific object. Thanks.
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