Collision of two objects

  • #1
146
10
Suppose there are two objects, denoted by A and B. When they collide with each other with the condition that A is stationary and B is in motion, B exerts an action force on A due to which A exerts a reaction force on B. Thus the net force exerted on A is FactionAB and the net force exerted on B is FreactionBA. Same is the case when A is in motion and B is at rest. But when A and B collide when they are in motion, the net force exerted on A is FactionAB + FreactionAB and the net force exerted on B is FactionBA + FreactionBA.
Question: Is my reasoning correct for the case when A and B collide when they are in motion? Is the net force exerted on A and B when they collide when they are in motion greater in magnitude than the net force exerted on A and B when they collide when only one of them is in motion?
 

Answers and Replies

  • #2
PeroK
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
17,538
9,268
The force depends how fast they are moving relative to each other.

In fact, all three scenarios are essentially the same: the same collision in different frames of reference. If you wanted to analyse a collision where both objects are moving it's a good idea to change your reference frame to one in which only one object is moving.

Finally, for this reason, there is only really one pair of action -reaction forces in each case.
 
  • Like
Likes donaldparida
  • #3
146
10
@PeroK, Is it possible to explain that there is one pair of action-reaction forces without changing the frame of reference?
 
  • #4
A.T.
Science Advisor
11,290
2,678
Question: Is my reasoning correct for the case when A and B collide when they are in motion?
No, you got confused by the physically meaningless "action / reaction" terminology.

Is it possible to explain that there is one pair of action-reaction forces ...
There is one pair of equal but opposite forces, because there is one interaction. Forget the "action / reaction" labels. The case where both move shows why they are meaningless.
 
  • #5
Chandra Prayaga
Science Advisor
650
149
As A.T says, there is only one force exerted by A on B and only one force exerted by B on A. These two forces are equal in magnitude and opposite in direction. This does not depend on which is moving and which is not. This is so in all cases.
 
  • #6
58
3
"action" an "reaction" are only logical concepts, who is who is relative, if we take the reference frame of one of the objects we can consider the moving object is "acting" and the stopped object "reacting" but in a third reference frame we would only have two objects colliding, the forces must be opposite so that the momentum is conserved.
 

Related Threads on Collision of two objects

  • Last Post
2
Replies
37
Views
3K
  • Last Post
2
Replies
41
Views
19K
  • Last Post
Replies
6
Views
2K
  • Last Post
5
Replies
117
Views
21K
  • Last Post
Replies
17
Views
3K
  • Last Post
Replies
4
Views
2K
Replies
13
Views
2K
  • Last Post
Replies
1
Views
562
  • Last Post
Replies
5
Views
812
Top