Normal force acting on a ladder lying against a wall

Click For Summary

Homework Help Overview

The discussion revolves around the concept of normal forces acting on a ladder positioned against a wall, specifically focusing on the definitions and orientations of these forces in free body diagrams. Participants are exploring the implications of friction and the correct representation of forces in such scenarios.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are questioning the definition of normal force and its orientation in relation to the surfaces involved. There are discussions about the effects of friction on the normal forces and whether they remain perpendicular in all cases. Some participants present diagrams to support their reasoning and challenge others' interpretations.

Discussion Status

The discussion is active, with multiple interpretations of the diagrams being explored. Some participants have offered clarifications about the nature of normal forces and the role of friction, while others are seeking further understanding of the concepts involved. There is no explicit consensus on the correct representation of forces yet.

Contextual Notes

Participants mention specific conditions such as the presence of friction between the ladder and both the ground and the wall, which complicates the understanding of normal forces. There is also a reference to a specific problem that may not have been fully shared, leading to some confusion about the diagrams being discussed.

starwars32
Messages
17
Reaction score
0
Hi.. I am just confused normal forces. The definition of normal force is always perpendicular to the surface. But when we draw a free body diagram for a ladder lying against the wall. The normal force is like slanted towards the wall. Please explain thanks.
 
Physics news on Phys.org
starwars32 said:
But when we draw a free body diagram for a ladder lying against the wall. The normal force is like slanted towards the wall.
No, the normal force between the wall and ladder is always perpendicular to the wall. By definition! But if there's friction on that wall, the wall may also exert a vertical force on the ladder.
 
Hi there. Here is my two diagrams. The correct answer is the first one. Why can't it be the 2nd one? the normal force acting on the ladder on the ground,shouldnt it be perpendicular to the ground ( normal force definition)? for the normal force on the wall due to the wall also shouldn't it be perpendicular too?Thanks
Untitled.png
 
starwars32 said:
The correct answer is the first one.
Who says?

I'd say that the second diagram is the correct one. (Assuming no friction between ladder and wall.) The first diagram doesn't make sense.
 
The qn given was that it has friction between the ladder and the ground and also between the ladder and the wall cos to prevent the ladder from slipping. So if we taken into account of friction then the normal force will not be perpendicular? y is it so?
 
starwars32 said:
The qn given was that it has friction between the ladder and the ground and also between the ladder and the wall cos to prevent the ladder from slipping.
Are you sure? You don't need friction between ladder and wall to prevent slipping, only between ladder and floor.

Why don't you post the exact problem that those diagrams are supposed to describe.
So if we taken into account of friction then the normal force will not be perpendicular? y is it so?
No. The normal force is always perpendicular to the wall.

(If I were drawing a diagram, I would always show the forces at wall and floor in terms of vertical and horizontal components. Much cleaner that way.)
 
QN: A ladder of weight W rests against a vertical wall. Friction between the ladder and the ground and also between the ladder and the wall prevents the ladder from slipping. Which diagram shows the directions of the forces on the ladder? The answer given was C. So the forces that is shown is not the normal forces? both on the ground and wall?
Physics.png
 
anyway if we like draw the net force, wouldn't we be drawing the net force instead of the forces that is acting on it? for free body diagrams we are always drawing the indidivual forces? am i right?
 
starwars32 said:
So the forces that is shown is not the normal forces? both on the ground and wall?
Correct. They are showing the total force of wall on ladder and floor on ladder, not just the normal force.

Do this. Show the components (normal force and friction), then add the components to see how the total force points at some angle.
 
  • #10
Ok thanks. Here is another qn on free body diagram. A crane is made from a uniform rigid boom of length 30m and weight 400N, as shown. The boom is supported at its lower end by a frictionless hinge on the ground. ITs upper end is attached to a support case that is fastened on the ground behind the boom. The support cable has variable length, hence allowing the boom to elevate the load. In a particular application, the crane is used to support a crate of weight 2.0 kN. The boom makes and angle of 45 degrees with the horizontal and the support cable makes an angle of 30 degrees with the horizontal. Complete a free body digram of the boom showing all forces acting on it. Label each force clearly. My qn: I thought they are merely asking for the forces not NET force. how come the reaction force on the floor is the first one and not the 2nd one? thanks
Physics 2.png


Physics 3.png
 
  • #11
starwars32 said:
anyway if we like draw the net force, wouldn't we be drawing the net force instead of the forces that is acting on it? for free body diagrams we are always drawing the indidivual forces? am i right?
Yes. In a free body diagram, one shows all the forces acting on the ladder: gravity, force of wall, force of floor.

But you can represent the force of wall on ladder by its components (normal force and friction) or by a single force vector that includes everything (like they do in this example). If you were actually solving a numerical problem, most likely using the components would be more useful. In this particular problem, they just want to test if you know which way the forces are acting.
 
  • #12
starwars32 said:
My qn: I thought they are merely asking for the forces not NET force.
They are just asking for the forces acting on the boom, not the components of those forces.
how come the reaction force on the floor is the first one and not the 2nd one?
The floor is attached to the boom. Why would you assume that it can only exert a vertical force? (There'd better be a horizontal component, otherwise what will balance the horizontal component of the cable tension?)
 
  • #13
ok thanks! appreciate it!
 
  • #14
woahhh thanks for this! i was getting stuck in my own physics and found this online :) anw just to clarify, in real life there isn't such thing as a frictionless wall so the correct resultant force on the ladder from the wall is never perpendicular to the wall right?
 

Similar threads

Normal force at the base of a ladder
  • · Replies 20 ·
Replies
20
Views
2K
Direction of the normal force when acting on a tilted object
  • · Replies 9 ·
Replies
9
Views
3K
Book plots position & force on the same graph, still gets right answer
  • · Replies 8 ·
Replies
8
Views
1K
Force of the wall against the ladder is from static friction?
  • · Replies 6 ·
Replies
6
Views
3K
Does a massless string cause a normal force when attached to a wall?
  • · Replies 2 ·
Replies
2
Views
2K
How Does the Direction of Normal Contact Force Affect Shelf Stability?
  • · Replies 7 ·
Replies
7
Views
3K
Force of the Ladder on a Wall Torque
  • · Replies 5 ·
Replies
5
Views
3K
Ladder on a wall held in place by a peg
  • · Replies 3 ·
Replies
3
Views
5K
Doubt related to buoyant force and fluid thrust force
  • · Replies 9 ·
Replies
9
Views
2K
Potential Mistake in Free-Body Diagram
  • · Replies 5 ·
Replies
5
Views
2K