Basics of Kinematics

Referential, movement, rest and trajectory are basic concepts of Kinematics, part of Physics that studies the movements.

Frame, motion, rest and trajectory are basic concepts of kinematics
Kinematics is the part of Mechanics that studies movements without worrying about their origins. Some concepts of kinematics are very important for the correct understanding of physical phenomena and a full understanding of the way to build the reasoning necessary for solving problems.

♦ Kinematics concepts:

→ Reference: The frame of reference is the body from which observations of phenomena are made. As an example, we can imagine that passengers inside a car, taking the vehicle as a reference, will be at rest; but taking a fixed point outside the car, all passengers will be in motion.

→ Movement and rest: From the concept of reference, we can understand that movement and rest are relative concepts, because what is in motion for an observer in a given reference can be at rest for another observer and vice versa.

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If the Earth is taken as a reference, we can say that buildings, cities, countries, everything is at rest. However, if the Sun is taken as a reference, the Earth and everything on its surface have rotation and translation movements .

→ Trajectory: is the path taken by a body that moves in relation to a referential. This concept is also relative, as two different references can have different views of the same movement. Imagine an aircraft releasing a cargo of supplies mid-flight. The image below shows the trajectories of the payload seen by an observer inside the aircraft and by someone on the ground.

For a passenger on the aircraft, the trajectory of the load is straight; but for someone on the ground, the trajectory is a curve, as the load follows the aircraft.

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