الميكانيك .. الفيزياء

Mechanics .. Physics

Mechanics

The graphs on the previous page provide us with the means to link the body's speed and acceleration (the rate of change of its speed) on the one hand, and the time and distance it travels during this time on the other hand. If we symbolize the initial speed of the body with the letter S, and its final speed with the letter E after the passage of time N, its acceleration becomes A, which is the slope of the graph and equals (E - S) / N.

As for the area between the graph and the time coordinate axis, it represents the value of the distance traveled during time N.

These concepts are limited to studying the changes in motion itself without considering the forces causing them. It is worth noting that the relationship between force and acceleration was not known until Newton discovered that all bodies usually continue their movement at a constant speed until a certain force is applied to them. Newton's discovery was called "the first law of motion".

As for the "second law of motion", it is a specific explanation of the concept of force. This is because the rate of change of the body’s velocity (its acceleration or deceleration A) is directly proportional to the force acting on it F according to the equation F = K × A, where K represents the body’s mass. The newton (Nt) is the unit used to measure force in the metric system of units and measures (known as the International System of Units, and it represents the force required to give a mass of one kilogram (kg) an acceleration of one meter per second (m/s2).

Mass and weight are two different things. According to Newton's equation, weight, which is the force of gravity on the body, is equal to the product of its mass and the acceleration of gravity of the Earth, i.e., W = m × g. Unfortunately, the two words are commonly used with the same meaning in everyday conversation. However, it is necessary to distinguish between them in the field of physics. Mass is measured in kilograms, while weight is measured in units of newtons.

As for the "third law of motion", it states that there is a force that is opposite to every existing force, and equal in value. If a book is placed on a table, it is under the influence of its weight, which is a force directed downward. However, it is not the only force present, as there is also the reaction of the table, which is equal to the weight of the book and is directed upward, and thus prevents the book and the same method is found in the principle of Rocket work, where it moves. The ignition of the fuel produces a downward thrust force, the reaction of which moves the rocket upward.

The graph of the speed of an accelerating body with respect to time. The acceleration is equal to A = AC / B C = (A - S) / N and the speed becomes A = S + A N.
As for the distance traveled by the body in time N, it is represented by the area below the graph
F = S N + 1/2 A N2.
These equations, if combined together, give
F = 1/2 (S + A) N, and also give A 2 = S 2 + 1A F.

Newton's third law of motion allows us to calculate the ignition time N required for the rocket to reach escape velocity, so if A and we consider that D is the reaction thrust, and the force pulling the rocket down is (its weight) K C, we have the following equation: D - K C = K A. Since A = A, time N = m A / (d - m J) (this is if we assume that fuel consumption changes the speed of the rocket).