Hello my friends of steeming I'm glad to write for You once again. To day I bring the final part of the serie I have titled "Explaining Newton's three laws using masterpieces of painting" where I have tried to show that is possible to teach physics through masterpieces of painting, we have found a useful tool to explain physical phenomena in a easy and interesting way to the traditional teaching, making this more attractive for all people.
I will close the article explaining the Newton's 2nd. law, this law gives us the practical basis to make calculations of displacement. As we can remember from the first part of the article, Newton said that the movement is caused by the force, I mean, to move a body we have to apply a force (or forces), and this forces must be unbalanced (its sumation must not be equal to zero), then when this happens, we will have two possible consequences depending of the state of movement of the body: 1) if the body is at rest, the unbalanced forces will change the velocity of the body from zero to a certain value. 2) if the body moves but with constant velocity, the unbalanced forces will change the velocity of the body from a certain velocity to other different that can be greater or less than the first velocity, even more, the final velocity could be zero. Therefore in both cases we have a common denominator which is: change in the velocity of the body and the change in the velocity we know it as acceleration.
So, we are ready to write the statement of Newton's 2nd. law: "the force is directly proportional to accteleration, in other words, if the force increases or decreases, the acceleration increase or decrease in the same proprotion to the force. but, at the same time, force is inversely proportional to the mass of the body, because this (the mass of the body) resists movement (Newton's 1st. law), therefore, if the mass is big then the acceleration will decrease and in the opposite way, if mass is small, the acceleration will increase, this can be write as: force = mass x acceleration".
But we must remember, force never acts alone, allways acts in pairs, I mean, we have more than one force, therefore, the formula of the second law can be write as: sumatory of forces = mass x acceleration.
To show better Newton's second law, see figure 1. this is a masterpiece painted by Giovanni Doménico Tiépolo and titled: "the trojan horse parade inside trojan". There we can see how the big wooden horse is moved by the trojans.
Figure 1
There we can see and put all the forces acting: the normal (green arrow), the weight (purple arrow), the force of the people pushing (light blue arrow), the force of the people pulling (red arrow) and the friction force (gray arrow), and the direction of movement is indicated by the yellow arrow. So, starting from this fgure, we can extract the free-body diagram to analyze better all the forces, this is shown in Figure 2.
Figure 2
In the free-body diagram we can see the normal is pointing up in the direction of positive vertical axe and the weight pointing in the opposite direction of the normal force, in the horizontal axe we have the frction force pointing in the direction of negative horizontal axe. But the force of push (that we call F1) and the force of pull (that we call F2) are not in the horizontal or vertical direction but between both horizontal and vertical direction, so it's necessary to do a decomposition of forces in order to apply Newton's 2nd. law. Force of push (F1) decomposes in two forces, one poiting in the possitive horizontal direction that we call F1H (at right, dotted light-blue arrow, Figure 2) and the other pointing in the positive vertical direction called F1V (up, dotted light-blue arrow, Figure 2), in the same way, the force of pull (F2) decomposes in two forces, one pointing in the positive horizontal direction (at right, dotted red arrow, Figure 2) and other pointing in the negative vertical direction (down, dotted red arrow, Figure 2).
Now, we have graphically defined all the forces, so we can apply Newton's 2nd. law at both axes as follows:
sumatory of vertical forces = normal + F1V - weight - F2V = 0. In this case, the vertical forces are in balance because there is no movement in the vertical direction. Now for the horizontal direction we write:
sumatory of horizontal forces = F1H + F2H -Friction force = mass x acceleration. this forces are not in balance, hence, we have movement.
Finally, we can connect 1st. and 2nd. Newton's law through acceleration, because we only have two ways to said that acceleration is equal to zero: 1) when velocity is equal to zero (when the body doesn't move or is at the rest) and 2) when the velocity is constant (remember acceleration = change in the velocity) therefore, if the velocity doesn't change there is not acceleration and sumatory of external forces = 0. This answers the question left in the previous post (please see: https://steemit.com/steemiteducation/@zambranoacosta/explaining-newton-s-three-laws-using-masterpieces-of-painting-part-ii).
Now we can say as a conclusion that effectively is possible explain physical phenomena through masterpieces of painting, as a final reflection I left to You, I hope that next time You see a masterpiece of painting, You can be able to see and explain physical phenomena present there, remember, painters and scientist are seeing the same thing: Nature.
Thanks for see and vote this articles, I'm very glad to shou You a different alternative to learn about Physics, my intention is to show that beyon tedious mathematics calculations and complicated formulas there is a wonderful science that teaches us the wonders of nature.
This article is based on the article written by one of my best friend 
References:
Wagner L. Christian (2008) Luz, Arte y Física: la física en la pintura. Cádiz, España (Light, Art and Physics: the physics in the painting. Cádiz Spain)
Hewitt, Paul (1992) Concepts of physics.