Newton's 2nd Law confusion: mass times acceleration is not a force?

[jbriggs444]

After being asked to read the thread and try not to miss the point...

Okay thanks I accept the suggestion

Continuing to miss the point...

I was never saying they were thee same thing we were saying they are equal and e = mc² is Einstein's equation of special relativity and here we are talking about force not energy.

 

[jack action]

I was never saying they were thee same thing

Yes you did:

So let me prove that mass time acceleration is a force.

According to generalized version of newton's second law,

F = dp/dt
We know that
P = m x v
F = dmv/dt
F = m (dv/dt)
F = m ( v/t)
We know that v/t = a
F = ma ( Hence proved)

All you did was prove they have the same value (being equal), not that they are the same thing:

In mathematics, equality is a relationship between two quantities or expressions, stating that they have the same value, or represent the same mathematical object.

Please prove that f is not equal to product of m and a.

Now you changed the statement from "mass times acceleration is a force" to "mass times acceleration equals a force". Nobody ever said they weren't equal.

describe what you claim that force is not equal to the product of mass and acceleration.

Again, nobody ever claimed that in this thread. What @PeroK said was that Newton stated that $F=ma$ based on his observations. We cannot prove it. The only reason we think it is true is that we cannot think of an experiment where this statement wouldn't be true, thus proving it to be wrong.

 

[PeroK]

Force, mass and acceleration are measurable physical quantities. If we measure these in consistent units, then there is a mathematical equality between the quantities $\vec F_{net} = m\vec a$. Sears and Zermansky emphasise the difference between this mathematical equality and things being the same measurable quantity. As I said in post #5, this seems like good practical advice in terms of understanding physics.

Another good example is $V = IR$. Voltage equals current times resistance. But, that's different from saying that current times resistance is a voltage.

 

[StandardsGuy]

Most of the responses here are lacking explanations - mostly just arrogant gibberish. When a rocket (unpowered) slingshots off a planet by the pull of it's gravity, it leaves the vicinity of the planet with greater speed that when it approached. How did the rocket obtain higher speed if no force acted upon it?

 

[jbriggs444]

Most of the responses here are lacking explanations - mostly just arrogant gibberish. When a rocket (unpowered) slingshots off a planet by the pull of it's gravity, it leaves the vicinity of the planet with greater speed that when it approached. How did the rocket obtain higher speed if no force acted upon it?

In the Newtonian model it obtains a higher speed due to the force of gravity.

This thread is not a dispute about whether $\sum F = ma$. It is (if anything) about drawing a distinction between the numeric quanty $ma$ and the physical concept of a force.

It seems to me that you have imagined some sort of straw man here. Maybe you think that someone is claiming that $\sum F \ne ma$. Or that gravity is not a force. It is hard to be sure since you have not quoted the point that you wish to rail against. Nor have you made a reasoned argument for an opposing point.

 

[Herman Trivilino]

Grateful if someone could explain why, if Newton's 2nd law says F=ma, I've read warnings and cautions in several physics books that mass times acceleration is not a force.

Because it's the sum of all the forces.

Law II tells us that the mass of a particle, times its acceleration, equals the sum of all the forces acting on that particle.

 

[weirdoguy]

mostly just arrogant gibberish

Prove it. Because I see none.

 

[L Drago]

In the Newtonian model it obtains a higher speed due to the force of gravity.

This thread is not a dispute about whether $\sum F = ma$. It is (if anything) about drawing a distinction between the numeric quanty $ma$ and the physical concept of a force.

It seems to me that you have imagined some sort of straw man here. Maybe you think that someone is claiming that $\sum F \ne ma$. Or that gravity is not a force. It is hard to be sure since you have not quoted the point that you wish to rail against. Nor have you made a reasoned argument for an opposing point.

Yeah. You are right. If someone wants us to prove a point. He should mention it.

 

[A.T.]

... gravity ... no force acted ...

Weird

 

[L Drago]

Most of the responses here are lacking explanations - mostly just arrogant gibberish. When a rocket (unpowered) slingshots off a planet by the pull of it's gravity, it leaves the vicinity of the planet with greater speed that when it approached. How did the rocket obtain higher speed if no force acted upon it?

This is weird. You first need to describe what do you think is right. Just as my perspective was chagen as now I understand that mass times acceleration is not the same as force, it is just an equivalence which is described by Newton's second law. A big thanks to @PeroK for changing my perspective. Now I realise what was describe in the book which cautioned against stating the product of mass and acceleration the same as force.