Topic 1 Newton’s first law of dynamics

“Each body continues in its state of rest or of uniform motion in a straight line, unless compelled to change that state by forces applied to it.“

According to Newton, a body is never truly inert, still, quiet: motion seems to be always present, albeit imperceptibly.

A body moves with uniform motion in a straight line when it moves along a straight line with constant speed.

In other words, a body that moves with uniform rectilinear motion (in the absence of friction) will continue its motion indefinitely until a force stops it, and therefore, when the force acting on a body is zero, its acceleration is also zero.

We can therefore define as an inertial frame of reference any frame of reference in which Newton’s first law is valid.

By inertia we mean the tendency that an object has to remain at rest or in uniform motion.

Experience teaches that an initially stationary body does not start moving without the intervention of an external cause. This cause is constituted, in general, by a force applied to the body in question.

Forces thus appear primarily as causes of motion. However, it is said that a body to which a force is applied doesn’t always put it in motion: this will generally only happen when the body is actually free to move, i.e. when there are no constraints capable of neutralizing the effect of an applied force.

For example, all bodies due to their weight tend to move vertically downwards. The weight of a body is therefore a force. However, if the body rests on a plane, is supported by our hand, etc., that is, it is bound, it cannot move. It can therefore be said that the effect of a force is to set in motion the body to which it is applied, or to produce a deformation of the constraints that prevent the body from moving. In general, forces can be exerted through physical contact between bodies, we then speak of contact forces.

I recommend reading a text and using it in this case about weight and lightness.

Six memos for the next millennium, Italo Calvino.

This book, then, is Calvino’s legacy to us: those universal values he pinpoints for future generations to cherish become the watchword for our appreciation of Calvino himself.

What about writing should be cherished? Calvino, in a wonderfully simple scheme, devotes one lecture (a memo for his reader) to each of five indispensable literary values. First there is “lightness” (leggerezza), and Calvino cites Lucretius, Ovid, Boccaccio, Cavalcanti, Leopardi, and Kundera–among others, as always–to show what he means: the gravity of existence has to be borne lightly if it is to be borne at all.

In the first part of the laboratory practice we will deal with walking and perceiving our feet establishing a conscious relationship with the floor by working on the coordination of walking and the movements of twenty-six bones, thirty-three joints and more than a hundred muscles, tendons and ligaments. The metatarsal will be at the center of the walking movement and, after having increased and decreased the speed of our walks, we will tackle the run. This type of exercise will be done both by working in silence, listening to the walking movement, and by using a metronome (which by the way is based on the physical law of oscillation of Newton’s pendulum: its rod sways in relation to the force of gravity exerted on the weight attached to its end).

Participants will be arranged in random order in space and guided by a series of commands to investigate on the condition of their bodies.

After this “warm-up” other indications will follow to feel and identify the floor with the whole body.

Use objects with different weights/shapes and test how this affects our body and our movements


[Material: Second Class of Gymnasium (B3.5)]

Duration: 5-10’

Mathematical analysis: Circle Area (circular disc) e = π r2

A circular disc is part of the plane enclosed by a circle.

To calculate the area of a circular disc, we divide the circular disc into slices as small as we possibly can. We cut these slices and then place them as shown in the figure:

We observe a series of triangle-like shapes, whose “bases” add up to the length of the circle, that is 2π × r, and whose “height” is equal to the radius of the circle. Therefore, the area of the circular disc is equal to the area of the triangles thus formed, that is, with r × 2 π r / 2
The area of the circular disc of radius r therefore equals E = πr2 .