- #1

- 1,067

- 92

https://www.feynmanlectures.caltech.edu/I_08.html Page 9-3. It says “In these terms, we see that Newton’s second law, in saying that the force is in same direction as the acceleration,is really three laws, in the sense that the components of force in the x, y,z directions is equal to the mass times the rate of change of corresponding components of velocity:

##F_x=m\frac{dv_x}{dt}=m(\frac{d^2x}{dt^2})=ma_x##

…..and so on”

I want to ask I can see there is second law and first law. First law because without force there is no change in velocity.

Just below that there are three components of forces. Everyone of them includes ##\cos##. Is it right?

On page 9-2 he says in the first paragraph ”Now there are several points to be considered. In writing down any law such as this we use many intuitive ideas………we say, it does not change.”

##F_x=m\frac{dv_x}{dt}=m(\frac{d^2x}{dt^2})=ma_x##

…..and so on”

I want to ask I can see there is second law and first law. First law because without force there is no change in velocity.

**But where is third law here?**Just below that there are three components of forces. Everyone of them includes ##\cos##. Is it right?

**Shouldn’t it be cos, sin, etc**That is how we resolve vectors into components.On page 9-2 he says in the first paragraph ”Now there are several points to be considered. In writing down any law such as this we use many intuitive ideas………we say, it does not change.”

**So he is basically saying Newton thought mass is independent of velocity and therefore he came of this law but later it was shown mass do depend on velocity. So his law is actually wrong.**
Last edited: