# Kinematics in physics: definition, concepts and examples

Kinematics is the branch of physics that studies the movement of objects and their trajectory as a function of time without taking into account the causes that produce it.

In the study of kinematics, the chemical and physical properties of moving bodies are not taken into account, with the exception of dimensions, as well as the forces acting on them. For this reason, it is also known as rigid solid kinematics.

This branch of physics is included within classical physics, so the formulas that we will present in the articles in this section do not take into account Einstein's theory of relativity. That is, the equations that we will present are only valid for small speeds compared to the speed of light.

## Basic concepts

To understand this branch of physics, it is essential to familiarize yourself with some basic concepts:

### 1. Position

The position of an object refers to its location in space relative to a reference system. It can be described using coordinates, such as a Cartesian coordinate system (x, y, z), where x, y, and z represent the spatial dimensions.

Position is typically represented by a vector indicating both the magnitude (distance) and direction from the origin of the reference frame.

### 2. Displacement

Displacement is a change in the position of an object.

It is expressed as a vector that connects the initial position with the final position of the object. Displacement is independent of the path followed by the object and is measured in terms of length and direction.

### 3. Velocity

The velocity of an object refers to the rate of change of its position with respect to time.

It is expressed in terms of displacement per unit of time and is represented as a vector. The speed can be constant (uniform motion) or change with time (accelerated motion).

### 4. Acceleration

Acceleration is the rate of change of an object's speed with respect to time.

Like velocity, it is represented as a vector. Acceleration can be positive (increase in speed), negative (decrease in speed), or zero (uniform motion).

### 5. Time

Time is a fundamental variable in kinematics that is used to measure the duration of an event. It allows us to describe how the other kinematic variables change over time.

## Types of movements

In the two-dimensional representation of kinematics there are several types of movement that can be summarized as follows:

• Uniform rectilinear motion (MRU) : In this type of motion, an object moves in a straight line at a constant speed, with no change in the magnitude or direction of the speed.
• Uniformly accelerated rectilinear motion (MRUA) : In MRUA, an object experiences a constant change in its speed, either an increase or a decrease, over equal time intervals.
• Uniform Circular Motion (MCU) : In MCU, the angular velocity remains constant while the object moves in a circular path.
• Uniformly Accelerated Circular Motion (UACM) : UAM involves a constant change in the angular velocity of an object in circular motion.
• Parabolic motion : In parabolic motion , an object follows a curved path that resembles a parabola, resulting from the combination of horizontal and vertical motion.
• Simple harmonic motion. The direction of the force under which the object moves is always opposite to the displacement and the magnitude is proportional to the displacement.

## Examples of kinematics

Kinematics manifests itself in various situations in everyday life and in scientific fields.

### Movement of a car

A common example is the movement of a car along a straight road at a constant speed, which conforms to the concept of uniform rectilinear motion (MRU).

When this car accelerates or brakes, such as when starting from a traffic light or slowing down to stop, this is an example of uniformly accelerated rectilinear motion (MRUA).

At the moment when the car takes a curve, the formulas of uniform circular motion (MCU) or uniformly accelerated circular motion (MCUA) can be applied if inside the curve it is braking or accelerating.

### Sports

In the sports field, kinematics is applied when analyzing the throwing of a baseball, where the trajectory of the ball follows a parabolic movement .

### Astronomy

In astronomy, it is used to study the movement of planets around the Sun and calculate their orbits.

### Nuclear power plants and nuclear physics

In nuclear physics, kinematics is used to analyze the collision of subatomic particles in particle accelerators.

In addition, nuclear power plants have steam turbines that, when in operation, experience circular motion.

## Difference between kinematics and dynamics

Kinematics and dynamics are two branches of physics that focus on different aspects of the motion of objects.

On the one hand, kinematics is concerned with describing movement in terms of position, speed and acceleration, without considering the causes that generate it. On the other hand, dynamics focuses on the study of the forces and interactions that cause the movement of objects.

That is, while kinematics is concerned with "how" objects move, dynamics focuses on "why" they move and how they respond to applied forces.

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Publication Date: February 16, 2022
Last Revision: July 5, 2022