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October 21, 2025, 06:53:09 pm

Author Topic: Help with Physics!!!  (Read 6877 times)  Share 

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paulsterio

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Re: Help with Physics!!!
« Reply #45 on: February 28, 2012, 11:07:14 pm »
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It does explain why the object is at rest. The sum of this upward reaction force and the downward weight force is zero.

the reaction force is not upwards?

and it is at rest due to friction which acts parallel to the slope up the slope. this is equal to the component of the weight force which is acting down the slope?

The force upwards? Where is this force upwards coming from?

the ground pushes up on the block

yawho

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Re: Help with Physics!!!
« Reply #46 on: February 28, 2012, 11:11:50 pm »
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It does explain why the object is at rest. The sum of this upward reaction force and the downward weight force is zero.

the reaction force is not upwards?

and it is at rest due to friction which acts parallel to the slope up the slope. this is equal to the component of the weight force which is acting down the slope?

The force upwards? Where is this force upwards coming from?

the ground pushes up on the block
What are the forces from the plane acting on the object?
the ground pushes up on the block? Did you mean the plane? If that was what you meant, it is not called reaction force of the plane on the object?
« Last Edit: February 28, 2012, 11:14:46 pm by yawho »

paulsterio

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Re: Help with Physics!!!
« Reply #47 on: February 28, 2012, 11:30:05 pm »
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This discussion is going nowhere.

The plane is pushing up on the object because the object is pushing down on the plane. The force which the plane acts on the object is called the reaction force?

What are you talking about?

yawho

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Re: Help with Physics!!!
« Reply #48 on: February 29, 2012, 07:29:45 am »
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This discussion is going nowhere.

The plane is pushing up on the object because the object is pushing down on the plane. The force which the plane acts on the object is called the reaction force?

What are you talking about?
Are you now saying the plane pushes the object with a upward force of 10 N? If that is the case, then it is called the reaction force of the plane on the object in N3L because the object pushes the plane with a downward force of 10 N. This was what my teacher said. But you said the reaction force is the normal force and not the 10 N upward force on the object.

thushan

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Re: Help with Physics!!!
« Reply #49 on: February 29, 2012, 10:04:35 am »
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Yawho - I'm sure you don't mean it, but you're coming across as a tad aggressive - so just watch your tone :P

Anyways, to answer that inclined plane question:

The 1 kg object on the inclined plane is AT REST. This means that the resultant force on the object is 0 N, via F = ma (Newton's 2nd Law).

There is the gravitational force from the Earth ON the object of 10 N going vertically down.
There is the frictional force on the object going up the plane.
There is the NORMAL reaction force on the object going perpendicular to the direction of the plane. Btw - normal = perpendicular.

What your teacher might have meant is that the frictional force is a reaction force of the plane on the block in a way because friction arises from the  rubbing of two rough surfaces where part of the object gets 'caught' within a microscopic cavity of the plane and pushes at it, and the plane pushes back up the object (reaction force) - and that constitutes friction. So the total reaction force is the sum of the normal reaction force + the frictional force (which one can argue is a reaction force too) = 10 N upwards - because the sum of those two forces must be equal and opposite to the gravitational force downwards (10 N) as the resultant force on object is 0 N.
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yawho

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Re: Help with Physics!!!
« Reply #50 on: February 29, 2012, 04:45:41 pm »
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Yawho - I'm sure you don't mean it, but you're coming across as a tad aggressive - so just watch your tone :P

Anyways, to answer that inclined plane question:

The 1 kg object on the inclined plane is AT REST. This means that the resultant force on the object is 0 N, via F = ma (Newton's 2nd Law).

There is the gravitational force from the Earth ON the object of 10 N going vertically down.
There is the frictional force on the object going up the plane.
There is the NORMAL reaction force on the object going perpendicular to the direction of the plane. Btw - normal = perpendicular.

What your teacher might have meant is that the frictional force is a reaction force of the plane on the block in a way because friction arises from the  rubbing of two rough surfaces where part of the object gets 'caught' within a microscopic cavity of the plane and pushes at it, and the plane pushes back up the object (reaction force) - and that constitutes friction. So the total reaction force is the sum of the normal reaction force + the frictional force (which one can argue is a reaction force too) = 10 N upwards - because the sum of those two forces must be equal and opposite to the gravitational force downwards (10 N) as the resultant force on object is 0 N.
I don't think I was aggressive in pointing out the inconsistency. Was my teacher right in saying the reaction force of the plane on the object is 10 N upward?
I read the original question again. It asked for the magnitude and direction of the reaction force, not for the analysis of the reaction force.
« Last Edit: February 29, 2012, 04:50:16 pm by yawho »

thushan

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Re: Help with Physics!!!
« Reply #51 on: February 29, 2012, 05:15:09 pm »
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Magnitude = 10 N.
Direction = upwards.

That's what I said before. And your teacher was right.

I was just explaining how the reaction force was 10 N upwards and wanted to clarify that it was the TOTAL reaction force, not the NORMAL reaction force (which you come across more often).
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yellowsone31

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Re: Help with Physics!!!
« Reply #52 on: March 07, 2012, 05:33:20 pm »
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What does it actually mean to be rank 1 in a SAC? Cause I was rank 1 for the first physics SAC and I have no idea what it actually means lol :)

paulsterio

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Re: Help with Physics!!!
« Reply #53 on: March 07, 2012, 05:49:01 pm »
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means next to nothing in one sac, you want to be ranked 1 overall

it means that you will get the highest exam mark in your cohort as your sac mark

Phy124

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Re: Help with Physics!!!
« Reply #54 on: March 07, 2012, 08:45:38 pm »
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What does it actually mean to be rank 1 in a SAC? Cause I was rank 1 for the first physics SAC and I have no idea what it actually means lol :)
If you maintain rank 1 you will get the highest scaled SAC scores (Highest General Assessment 1 score), within your school at the end of the year.

Never mind, beaten.
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yellowsone31

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Re: Help with Physics!!!
« Reply #55 on: March 07, 2012, 09:36:32 pm »
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means next to nothing in one sac, you want to be ranked 1 overall

it means that you will get the highest exam mark in your cohort as your sac mark

thanks !

yellowsone31

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Re: Help with Physics!!!
« Reply #56 on: March 07, 2012, 09:36:49 pm »
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What does it actually mean to be rank 1 in a SAC? Cause I was rank 1 for the first physics SAC and I have no idea what it actually means lol :)
If you maintain rank 1 you will get the highest scaled SAC scores (Highest General Assessment 1 score), within your school at the end of the year.

Never mind, beaten.

thanks for replying :)