localmemelord
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is the normal contact force the same type of force as the gravitational force(i.e. weight)?
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hustlr
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(Original post by localmemelord)
is the normal contact force the same type of force as the gravitational force(i.e. weight)?
The normal contact force is defined by the force which prevents an object from compressing

much like how the book doesn't smash through the table due to its weight (the hole made would be considered compression)

it is not restricted to weight however, I could punch a wall and a normal force would be exerted on my fist, equal in magnitude (given that the wall remains unchanged) because of newtons third law

the third law states that interacting bodies exert forces equal in magnitude and opposite in direction onto each other.

the normal contact and weight are different because, weight always acts downwards, however a normal contact force acts perpendicular to the surface.

For clarity, normal contact force is the force which resists an objects compression and acts perpendicular to the surface, and can be considered a consequence of newtons third law.

Tension on the other hand is the force which resists an object's EXTENSION, so tension and normal contact are considered opposites (in definition)
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localmemelord
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(Original post by hustlr)
The normal contact force is defined by the force which prevents an object from compressing

much like how the book doesn't smash through the table due to its weight (the hole made would be considered compression)

it is not restricted to weight however, I could punch a wall and a normal force would be exerted on my fist, equal in magnitude (given that the wall remains unchanged) because of newtons third law

the third law states that interacting bodies exert forces equal in magnitude and opposite in direction onto each other.

the normal contact and weight are different because, weight always acts downwards, however a normal contact force acts perpendicular to the surface.

For clarity, normal contact force is the force which resists an objects compression and acts perpendicular to the surface, and can be considered a consequence of newtons third law.

Tension on the other hand is the force which resists an object's EXTENSION, so tension and normal contact are considered opposites (in definition)
newton's third law also states that the forces are of the same type. so does this still hold?
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Stonebridge
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There are 2 types of force being considered here:
the 'gravitational' force you mention, and the normal contact force.
If, by 'gravitational' you mean the force of the Earth pulling down on the object, then that is contactless, action at a distance.
The normal reaction is a contact force.

You also used the word 'weight', but I will assume you mean the Earth/Mass gravitational attraction here.
While that gravitational force is often referred to as 'weight', the weight of an object is normally experienced as the force it pushes down with on the surface it is resting on. That actually would be a contact force.
So, the gravitational and normal reaction forces are not of the same 'type'. One is contactless and the other is contact.

btw.
The Newton's 3rd Law reaction to the gravitational force of the Earth on that mass, is the equal and opposite force of that mass pulling up on the Earth. They are of the same type, being both 'action at a distance'.

It can occasionally get confusing in discussions of 'weight', as to exactly which force is being referred to here.
Let me know if this helps.
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hustlr
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(Original post by Stonebridge)
There are 2 types of force being considered here:
the 'gravitational' force you mention, and the normal contact force.
If, by 'gravitational' you mean the force of the Earth pulling down on the object, then that is contactless, action at a distance.
The normal reaction is a contact force.

You also used the word 'weight', but I will assume you mean the Earth/Mass gravitational attraction here.
While that gravitational force is often referred to as 'weight', the weight of an object is normally experienced as the force it pushes down with on the surface it is resting on. That actually would be a contact force.
So, the gravitational and normal reaction forces are not of the same 'type'. One is contactless and the other is contact.

btw.
The Newton's 3rd Law reaction to the gravitational force of the Earth on that mass, is the equal and opposite force of that mass pulling up on the Earth. They are of the same type, being both 'action at a distance'.

It can occasionally get confusing in discussions of 'weight', as to exactly which force is being referred to here.
Let me know if this helps.
yeah so newtons third law in this casewould refer to the gravitational attraction by the bodies toward eachother? ( and not the consequence of weight and reaction force being equal and opposite as this would show newtons first law instead)?
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Stonebridge
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(Original post by hustlr)
yeah so newtons third law in this casewould refer to the gravitational attraction by the bodies toward eachother? ( and not the consequence of weight and reaction force being equal and opposite as this would show newtons first law instead)?
Yes to the first bit. The mutual attractive forces of Earth and mass would be the Newton 3 pair. Correct.
Well, for an object just sitting on a static table, it's weight (what we normally consider as the force it pushes down on the table with) would be equal and opposite to the normal reaction, and the Newton 3 pair of forces.. The mass pushes the table and the table pushes the mass.
To bring in Newton's first law, you would need to consider all the forces on the mass, here, the Earth's pull on the mass downwards, and the table pushing upwards. If the mass is not accelerating, these would be equal and opposite. They are not a Newton 3 pair, but just 2 different forces acting on the mass. If the resultant is zero, there is no acceleration.
Last edited by Stonebridge; 1 year ago
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