- #1
Rakinniya
- 9
- 0
People say that Newton's Second law is the real Law of Motion because both the First and the third law can be proved from the second. If this is true why did Newton state them as separate laws if they are just special cases of the 2nd law? My teacher taught us this.
These are the proofs she taught...
1)1st Law frm 2nd
In the eq
F=ma
when we put F=0 we get Acceleration = 0 ----> the first Law of motion
okay this is fine...
2)Now..3rd frm 2nd..
let two bodies interact
let F1 and F2 be the action n reaction
then according to the second law
F1=dP1/dt F2=dP2/dt
F1+F2 = d/dt (P1+P2)
when no external forces are acting... according to the law of conservation of momentum Momentum must be conserved
P1+P2=const
F1+F2 = d/dt (P1+P2)
F1+F2=0
F1= -F2 ----->third Law
But the problem I find here is ... We prove the Law of conservation of momentum by applying the third law ... Then isn't it silly and incorrect to use the momentum law to prove the third law...? ...
.. Please tell me if there is some other valid proof...or any changes that can be made in this one
These are the proofs she taught...
1)1st Law frm 2nd
In the eq
F=ma
when we put F=0 we get Acceleration = 0 ----> the first Law of motion
okay this is fine...
2)Now..3rd frm 2nd..
let two bodies interact
let F1 and F2 be the action n reaction
then according to the second law
F1=dP1/dt F2=dP2/dt
F1+F2 = d/dt (P1+P2)
when no external forces are acting... according to the law of conservation of momentum Momentum must be conserved
P1+P2=const
F1+F2 = d/dt (P1+P2)
F1+F2=0
F1= -F2 ----->third Law
But the problem I find here is ... We prove the Law of conservation of momentum by applying the third law ... Then isn't it silly and incorrect to use the momentum law to prove the third law...? ...
.. Please tell me if there is some other valid proof...or any changes that can be made in this one