Fictitious Forces ⇔ Constraint Forces? (re: D'Alembert's Principle)

  • Thread starter Geremia
  • Start date
  • #1
151
0

Main Question or Discussion Point

Are fictitious forces and constraint forces the same thing?
 

Answers and Replies

  • #2
122
1
No, fictitious forces are forces which arise from analyzing within a non-inertial reference frame. Constraint forces are those which arise from a geometrical configuration.

For example, a constraint force would be perhaps a normal force exerted by the surface an object rests on such as an inclined plane problem. As long as the object is on the inclined plane, the object's motion is constrained to be along the inclined plane.

For a fictitious force consider that the Earth is in fact a rotating reference frame and therefore non-inertial. This gives rise to the Coriolis force which is needed to correct calculations due to this fact. It is small in effect but needed especially in large-distanced calculations.
 
  • #3
151
0
No, fictitious forces are forces which arise from analyzing within a non-inertial reference frame. Constraint forces are those which arise from a geometrical configuration.
Yes, but how can geometry cause forces? Isn't force a change in momentum? Doesn't force imply movement? If a force isn't doing work, how is it a force?
For example, a constraint force would be perhaps a normal force exerted by the surface an object rests on such as an inclined plane problem. As long as the object is on the inclined plane, the object's motion is constrained to be along the inclined plane.
Yes, but what causes the constraint force, if not inertial effects?
 
  • #4
Andrew Mason
Science Advisor
Homework Helper
7,583
346
Yes, but how can geometry cause forces? Isn't force a change in momentum? Doesn't force imply movement? If a force isn't doing work, how is it a force?Yes, but what causes the constraint force, if not inertial effects?
Constraint forces self-adjust so that they are exactly equal and opposite to the force they are opposing. So they do not do work and they do not cause a change in momentum. They balance other forces that would otherwise do work/cause change in momentum.

AM
 
  • #5
Matterwave
Science Advisor
Gold Member
3,965
326
One should remember that NET forces produce a change in momentum. Any one individual force may or may not lead to a change in momentum.

A force is not required to do work. Work is the dot product of force and distance, so if the distance is 0, or if the force is applied perpendicular to the direction of motion, then the force does no work.
 

Related Threads on Fictitious Forces ⇔ Constraint Forces? (re: D'Alembert's Principle)

Replies
1
Views
2K
Replies
6
Views
264
  • Last Post
Replies
10
Views
1K
  • Last Post
Replies
2
Views
426
  • Last Post
Replies
12
Views
844
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
0
Views
2K
Replies
19
Views
691
  • Last Post
Replies
8
Views
2K
  • Last Post
Replies
7
Views
3K
Top