The second law

[Luigi Fortunati]

In my animation
https://www.geogebra.org/m/abg3ewgy
if we click on the "Start" button, we see the "net" force 10 which accelerates the mass of the elementary particle A towards the right (according to the second law F=ma) and no force directed towards the left.

So far I have nothing to ask because everything is clear.

Then we select the checkbox to add particle B.

In this case, there is no longer the single particle (A) but there is the body AB formed by the set of the two particles A and B, so that the mass doubles and the acceleration is halved.

The force F=10 acts only on particle A which transmits the push to particle B.

In this way, an action and reaction relationship is established between A and B: particle A exerts a blue force towards the right on particle B and particle B reacts with a red force towards the left on particle A.

Question 1: Is it correct to say that these two blue and red forces are worth 5 and –5 respectively?

Question 2: Is it correct to say that a "net" force (5) to the right acts on particle A (blue force 10 minus red force 5) and a net blue force (5) acts to the right on particle B?

Luigi Fortunati

[Richard Livingston]

Answer is yes to both questions, assuming both particles have the same mass.

Rich L.

[Luigi Fortunati]

Richard Livingston il 20/11/2023 17:10:20 ha scritto:
>> In my animation https://www.geogebra.org/m/abg3ewgy if we click on the "Start" button, we see the "net" force 10 which accelerates the mass of the elementary particle A towards the right (according to the second law F=ma) and no force directed towards the left.
>> So far I have nothing to ask because everything is clear.
>> Then we select the checkbox to add particle B.
>> In this case, there is no longer the single particle (A) but there is the body AB formed by the set of the two particles A and B, so that the mass doubles and the acceleration is halved.
>> The force F=10 acts only on particle A which transmits the push to particle B.
>> In this way, an action and reaction relationship is established between A and B: particle A exerts a blue force towards the right on particle B and particle B reacts with a red force towards the left on particle A.

>> Question 1: Is it correct to say that these two blue and red forces are worth 5 and –5 respectively?

>> Question 2: Is it correct to say that a "net" force (5) to the right acts on particle A (blue force 10 minus red force 5) and a net blue force (5) acts to the right on particle B?
>

> Answer is yes to both questions, assuming both particles have the same mass.

Thank you.

Therefore, this red force –5 exists and is the inertial reaction of particle B against anyone who tries to change its condition of rest.

I ask you: what difference is there between this red force –5 of my animation and the one that Newton (talking about inertia) describes like this: "a body exerts this force (inertia) only when another force, impressed upon it, endeavors to change its condition"?

Luigi Fortunati

[Luigi Fortunati]

In my animation
https://www.geogebra.org/m/abg3ewgy

there is a blue force 10 directed to the right which generates an acceleration 10.

If I want to reduce the acceleration from 10 to 5, I need to apply a red
force –5 (directed to the left) on mass A, so that the net force on mass
A becomes equal to 5 and the acceleration also drops from 10 to 5 .

However, there is also another way to obtain the same result (reduce the
acceleration of A) without applying any force, just add the mass B (with
the appropriate box).

In this way, mass B generates a red force –5 on mass A, halving its
acceleration.

How is it possible that adding mass B (which is a scalar) acts *exactly*
like the force F=-5 (which is a scalar)?

Luigi Fortunati