• Support PF! Buy your school textbooks, materials and every day products Here!

D' Alemberts principle

  • Thread starter almirza
  • Start date
11
0
1. Homework Statement

I am just not getting the benefit or the application of this principle. Why are we using it?
For example, in my text book I have the following example. A particle of mass (m) is attached via an inextensible string of length (R) to a fixed point O and moves on a horizontal circular path with constant angualr velocity. Determine an expression for the tension in the string (T).
It is solved by two ways. The first way is by concidering the forces applied on the particle and the tangention and radial accelerations. And since there is only centripetal accelearation, the only force acting is the tension and so T=ma and a = R * angualr velocity.
The second way is by D' Alemberts principle. It says that an imaginary inertia force of magnitude (ma) is acting in the opposite direction of the actual acceleration which equals R * angular velocity. And then just T-ma = 0 !!!
Why this way?
Why am I assuming an imaginary force?
My point is that surely I will need to concider the tangentional and radial accelerations as the first part of the solution to make sure that there is only centripetal accelaration acting toward the centre which equals (R * angular velocity) as I did in the first way and then I will assume that (am) is a force acting outwards the centre. So Why should I assume something like this and not just say T=am.



2. Homework Equations



3. The Attempt at a Solution
 

Answers and Replies

11
0
up up
 

Related Threads for: D' Alemberts principle

  • Last Post
Replies
1
Views
391
Replies
1
Views
7K
  • Last Post
Replies
6
Views
732
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
6
Views
1K
  • Last Post
Replies
0
Views
2K
Replies
2
Views
396
Replies
3
Views
2K
Top