lhh2003
Badges: 17
Rep:
?
#1
Report Thread starter 9 months ago
#1
I understand that gravity and the normal force are NOT an action reaction force pair. But this leaves me with the question of what actually causes the force to be exerted downwards on the table by the book to generate a normal force on the book acting upwards ?

Thanks.
0
reply
lhh2003
Badges: 17
Rep:
?
#2
Report Thread starter 9 months ago
#2
BUMP
0
reply
Stonebridge
Badges: 13
Rep:
?
#3
Report 9 months ago
#3
(Original post by lhh2003)
I understand that gravity and the normal force are NOT an action reaction force pair. But this leaves me with the question of what actually causes the force to be exerted downwards on the table by the book to generate a normal force on the book acting upwards ?

Thanks.
It's the other way round, really. The best way to think about it, is first to consider the forces on the book.
So, considering the book: It has its weight acting downwards on it, which, in the absence of any other force, will cause it to accelerate downwards. (Acceleration due to gravity)
If that was everything then it would indeed just fall. So let's put a table in the way.
To stop the book falling you have to apply an equal and opposite upwards force to its weight so that the resultant of that force and the book's weight is zero. Then you get zero resultant force on the book and it remains at rest.
So, the upwards force that is applied to the book is the force from the table. If the table wasn't there, there would be no upwards force.
So first comes the table's upwards force on the book. The Newton's 3rd Law reaction to that is the force of the book on the table.
Last edited by Stonebridge; 9 months ago
1
reply
lhh2003
Badges: 17
Rep:
?
#4
Report Thread starter 9 months ago
#4
(Original post by Stonebridge)
It's the other way round, really. The best way to think about it, is first to consider the forces on the book.
So, considering the book: It has its weight acting downwards on it, which, in the absence of any other force, will cause it to accelerate downwards. (Acceleration due to gravity)
If that was everything then it would indeed just fall. So let's put a table in the way.
To stop the book falling you have to apply an equal and opposite upwards force to its weight so that the resultant of that force and the book's weight is zero. Then you get zero resultant force on the book and it remains at rest.
So, the upwards force that is applied to the book is the force from the table. If the table wasn't there, there would be no upwards force.
So first comes the table's upwards force on the book. The Newton's 3rd Law reaction to that is the force of the book on the table.
So what you are saying that for book (b) and table (t) :

F t on b = F b on t = F weight of book ?
0
reply
Stonebridge
Badges: 13
Rep:
?
#5
Report 9 months ago
#5
(Original post by lhh2003)
So what you are saying that for book (b) and table (t) :

F t on b = F b on t = F weight of book ?
Yes, because they are Newton 3 action and reaction they must be equal in magnitude. And because the book's weight is balanced by the force from the table (it's why it is at rest) then both of those forces are equal to the weight of the book.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

What factors affect your mental health the most right now?

Anxiousness about lockdown easing (59)
4.66%
Uncertainty around my education (194)
15.32%
Uncertainty around my future career prospects (139)
10.98%
Lack of purpose or motivation (180)
14.22%
Lack of support system (eg. teachers, counsellors, delays in care) (56)
4.42%
Impact of lockdown on physical health (71)
5.61%
Loneliness (111)
8.77%
Financial worries (44)
3.48%
Concern about myself or my loves ones getting/having been ill (58)
4.58%
Exposure to negative news/social media (58)
4.58%
Lack of real life entertainment (68)
5.37%
Lack of confidence in making big life decisions (112)
8.85%
Worry about missed opportunities during the pandemic (116)
9.16%

Watched Threads

View All