Chapter : Newton's Laws Of Motion & Friction

7. Motion of connected Bodies

7. Motion of bodies in contact
Case (A) :
Two body system :
Let a force F be applied on mass m1.

Free body diagrams: (vertical force do not cause motion, hence they have not been shown in diagram)
For AFor B

F – f = m1a

f = m2a

(i) Here f is known as force of contact.
(ii) Acceleration of system can be found simply by
If force F be applied on m2, the acceleration will remain the same, but force of contact will be different i.e.
Case (B) :
Three body system :

Free body diagrams :
For AFor BFor C

F – f1 = m1a

f1 – f2 = m2a

f2 = m3a


f1 = contact force between masses m1and m2
f2= contact force between masses m2 and m3
Remember :
Contact force is different if force F will be applied on mass C

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