8. Motion of connected Bodies
Case (A) :
For two Bodies :
F is the pull on body A of mass m₁. The pull of A on B is exercised as tension through the string connecting A and B. The value of tension throughout the string is T only.
But this manifests as a pull T on B and a "reaction pull" T on A the free body diagram in this case are shown as follows.

Note : The spring is massless
Free body diagrams :

For body A	For body B
R1= m1g F – T = m1a	R2= m2g T = m2a

⇒
Case (B) :
For Three bodies :

Free body diagrams :

For A	For B	For C
R1= m1g T1= m1a	R2= m2g T2– T1= m2a ⇒ T2= m2a + T1 T2= (m2 + m1)a	R3= m3g F – T2= m3a ⇒ F = m3a + T2 = m3a + (m1 + m2)a F = (m1 + m2 + m3)a

⇒