Force applied to 2 connected mass.

Click For Summary

Discussion Overview

The discussion revolves around the dynamics of two connected masses, m1 and m2, with a force applied to m2. Participants explore the implications of tension in the connecting cord and the effects of the applied force on both masses, focusing on the nature of forces and reactions as described by Newton's laws.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that when a force F is applied to m2, m1 experiences a tension TA in the positive x-direction, while m2 experiences both the force F and a tension TB in the negative x-direction.
  • Others question why m1 does not experience a tension in the negative x-direction, suggesting that there should be an equal and opposite reaction according to Newton's third law.
  • Some participants clarify that the cord exerts a tension force on both masses, but the direction of these forces differs based on the applied force.
  • There is a suggestion that if a third mass were connected to m1, it would also experience a tension force acting in the negative x-direction.
  • Participants discuss the nature of action and reaction forces, with some emphasizing that m2 pulls on m1 and vice versa, in accordance with Newton's third law.
  • There is a recognition that the force F and the tension in the cord are not equal, indicating a nuanced understanding of the system's dynamics.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the forces acting on m1 and m2, particularly regarding the existence and direction of tension forces. The discussion remains unresolved, with multiple competing interpretations of the forces involved.

Contextual Notes

Some participants note that the lecturer did not outline the reactions clearly, leading to confusion about the presence of forces acting on the masses. There is also a mention of the need for clarity in understanding the implications of Newton's laws in this context.

negation
Messages
817
Reaction score
0
Untitled.png


A force is applied to m1 connected to m2 by a "massless" cord. where m2>m1.

the acceleration, a, is a = F/m1+m2

By decomposing the system into A and B where A refers to the tension on m1 upon having the force applied onto m2, the tension TA is to the positive x-direction.

However, in the case of the system B, the tension TB is to the negative x-direction as the force F is applied directly to m2.

Why does TB arises in the block m2 but yet not in m1?
 
Physics news on Phys.org
negation said:
Why does TB arises in the block m2 but yet not in m1?
I'm not sure I understand this statement. The cord connecting the two masses exerts a tension force on both m1 and m2. The cord exerts the same force on both blocks (different directions, of course).
 
Doc Al said:
I'm not sure I understand this statement. The cord connecting the two masses exerts a tension force on both m1 and m2. The cord exerts the same force on both blocks (different directions, of course).

I shall rephrase. I was lacking clarity in the OP.

When force F is applied on m2, m1 experiences a tension TA in the positive x-direction. (why shouldn't m1 experience another tension in the negative x-direction. By my understanding, there should be an equal and opposite reaction.

In the case of m2, upon the appliance of the force F, the m2 experience not only the force F in the positive x-direction but also a tension TB in the negative x-direction.
 
negation said:
When force F is applied on m2, m1 experiences a tension TA in the positive x-direction.
Right. Tension is created in the cord, which acts on both masses.

(why shouldn't m1 experience another tension in the negative x-direction.
What would create that tension?

By my understanding, there should be an equal and opposite reaction.
A reaction from what?

In the case of m2, upon the appliance of the force F, the m2 experience not only the force F in the positive x-direction but also a tension TB in the negative x-direction.
And if the mass m1 were connected to a third mass, then it too would experience a tension force acting to the left. But there is no third mass.

(Note that the force F and the tension in the cord are not equal.)
 
Doc Al said:
Right. Tension is created in the cord, which acts on both masses.


What would create that tension?


A reaction from what?


And if the mass m1 were connected to a third mass, then it too would experience a tension force acting to the left. But there is no third mass.

(Note that the force F and the tension in the cord are not equal.)


A reaction from m1 having experience a force F applied to m2?

Suppose, as you've suggested that a third mass m3 was attached to m1 to the left. If the same force F were applied, then aside from m2 having experienced the tension TB, m1 would now experience a tension in the negative x-direction, am I right?
 
negation said:
A reaction from m1 having experience a force F applied to m2?
I'm not sure what you mean by a 'reaction'. m2 pulls on m1 (via the massless cord) and m1 pulls back on m2.

Suppose, as you've suggested that a third mass m3 was attached to m1 to the left. If the same force F were applied, then aside from m2 having experienced the tension TB, m1 would now experience a tension in the negative x-direction, am I right?
Sure. The force F will end up creating various tensions in the cords connecting the masses.
 
negation said:
I shall rephrase. I was lacking clarity in the OP.

When force F is applied on m2, m1 experiences a tension TA in the positive x-direction. (why shouldn't m1 experience another tension in the negative x-direction. By my understanding, there should be an equal and opposite reaction.

In the case of m2, upon the appliance of the force F, the m2 experience not only the force F in the positive x-direction but also a tension TB in the negative x-direction.

Yes there is a reaction (Newton's 3rd law). What made you believe there isn't one?
 
Doc Al said:
I'm not sure what you mean by a 'reaction'. m2 pulls on m1 (via the massless cord) and m1 pulls back on m2.


Sure. The force F will end up creating various tensions in the cords connecting the masses.

Come on, Doc. he's talking about Newton's 3rd law. quoting from your post " m2 pulls on m1" - That's the action - "and m1 pulls back on m2" - That's the reaction.
 
dauto said:
Yes there is a reaction (Newton's 3rd law). What made you believe there isn't one?


I understand there to be one but it isn't outlined by my lecturer.
 
  • #10
dauto said:
Come on, Doc. he's talking about Newton's 3rd law. quoting from your post " m2 pulls on m1" - That's the action - "and m1 pulls back on m2" - That's the reaction.
That's why I used it as an example. But I don't think that's what was meant. (I think he was looking for a second force acting on the trailing block.)
 
Last edited:
  • #11
negation said:
I understand there to be one but it isn't outlined by my lecturer.

That doesn't mean it's not there.
 

Similar threads

High School Gravitational force between two masses
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Two-Mass Oscillator: Plotting Amplitudes Over Frequency in Hertz
  • · Replies 10 ·
Replies
10
Views
3K
High School Will Block M2 Move Left? Understanding Forces in a Connected Spring System"
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Force Applied -- General doubt about pushing 2 blocks on a floor with friction
  • · Replies 21 ·
Replies
21
Views
4K
Graduate Calculating Final Positions & Velocities for M1, M2 & Spring After DeltaT
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad 2 Masses connected by a spring
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Seeking intuition on movement of COM
  • · Replies 2 ·
Replies
2
Views
1K
How much force does the 20 kg block exert on the 10 kg block?
  • · Replies 17 ·
Replies
17
Views
2K
Undergrad How Does Releasing an Object Affect Tension in a Pulley System?
  • · Replies 2 ·
Replies
2
Views
2K
Irodov- 1.123- Simple conceptual question with two masses connected by a spring
  • · Replies 20 ·
Replies
20
Views
3K