Kinematics | Physics for Engineers Lesson 4

Kinematics is a branch of classical mechanics that deals with the study of motion of objects without considering the forces that cause or result from that motion. It is a fundamental aspect of physics and engineering, providing valuable insights into how objects move and interact in space and time.

The study of kinematics is primarily concerned with understanding and describing the motion of objects by analyzing various parameters such as position, velocity, and acceleration. These parameters can be represented mathematically using vectors and equations, allowing for a precise and detailed analysis of motion.

Key concepts in kinematics include:

  1. Position: The location of an object in space, usually represented by a vector (denoted as r) that defines the object’s coordinates in a given reference frame.
  2. Displacement: The change in position of an object over time, typically represented as a vector (denoted as Δr) that connects the initial and final positions.
  3. Velocity: The rate at which an object changes its position, often represented as a vector (denoted as v) that describes the object’s speed and direction of motion.
  4. Acceleration: The rate at which an object’s velocity changes, represented as a vector (denoted as a) that indicates the magnitude and direction of the change in velocity.
  5. Time: The independent variable used to describe the progression of motion, denoted as t.
  6. Equations of motion: Mathematical relationships that describe the motion of objects under constant acceleration. These include:

a. First equation of motion: v = u + at b. Second equation of motion: s = ut + ½at² c. Third equation of motion: v² = u² + 2as

Here, u is the initial velocity, v is the final velocity, a is the acceleration, t is the time elapsed, and s is the displacement.

Kinematics can be further divided into two subcategories:

  1. Rectilinear kinematics: The study of motion along a straight line.
  2. Curvilinear kinematics: The study of motion along a curved path.

Overall, kinematics provides a foundation for understanding how objects move and interact, which is essential for fields such as physics, engineering, robotics, and biomechanics.


Let’s consider a simple example of rectilinear kinematics involving a car moving in a straight line.

Suppose a car starts from rest (initial velocity u = 0) and accelerates uniformly at a rate of 2 meters per second squared (a = 2 m/s²) for a duration of 5 seconds (t = 5 s). We can use kinematic equations to find the final velocity (v) and the displacement (s) of the car during this time.

  1. To find the final velocity (v), we can use the first equation of motion:
    v = u + at
    v = 0 + (2 m/s²)(5 s)
    v = 10 m/s

So, the final velocity of the car is 10 m/s.

  1. To find the displacement (s), we can use the second equation of motion:
    s = ut + ½at²
    s = (0)(5 s) + ½(2 m/s²)(5 s)²
    s = 0 + 0.5(2)(25)
    s = 25 m

Thus, the car has traveled a distance of 25 meters during the 5-second period.

In this example, we used basic kinematic equations to analyze the motion of a car moving in a straight line. The simplicity of the scenario makes it easy to understand the concepts and calculations involved in kinematics.

Kinematics in Computer Engineering

In computer engineering, kinematics is often applied in fields such as computer graphics, robotics, and computer-aided design (CAD). It helps in understanding and simulating the motion of objects in virtual environments and designing algorithms for controlling the movement of robotic systems.

Here are some areas where kinematics is relevant to computer engineering:

  1. Computer Graphics and Animation: In computer graphics and animation, kinematics is used to model the motion of characters and objects in virtual environments. This involves using kinematic equations to determine the position, velocity, and acceleration of each element in a scene. Forward kinematics and inverse kinematics are commonly used techniques in animating characters or objects.
  • Forward kinematics refers to calculating the position and orientation of an object’s end effector (like a robotic arm or character’s hand) based on the angles and lengths of its joints or links. Given joint angles and link lengths, forward kinematics computes the resulting position of the end effector.
  • Inverse kinematics is the opposite process, where the desired position and orientation of the end effector are known, and the goal is to calculate the joint angles and link lengths required to achieve that position. This is particularly useful in animating characters or controlling robotic systems that need to reach specific targets.
  1. Robotics: In robotics, kinematics plays a critical role in designing algorithms for controlling the movement of robotic systems, such as robotic arms or mobile robots. Understanding the relationships between joint angles, velocities, and accelerations allows engineers to develop effective control strategies for these systems. Path planning, obstacle avoidance, and trajectory generation are some tasks where kinematics is essential in robotics.
  2. Computer-Aided Design (CAD): Kinematics is also applicable in the design and analysis of mechanical systems using CAD software. Engineers use kinematic simulations to study how various components of a mechanical system, such as gears, linkages, or joints, interact and move relative to one another. This enables them to optimize the design for performance and efficiency, ensuring that the system operates as intended.

In summary, kinematics is a vital aspect of computer engineering, particularly in computer graphics, robotics, and CAD. By understanding the principles of motion, engineers can develop algorithms and tools to simulate, control, and optimize the movement of objects and systems in various applications.


Let’s consider an example in computer engineering, specifically in the field of robotics, where we have a simple 2-link robotic arm. We will use kinematics to find the position of the end effector, given the lengths of the links and the joint angles.

Suppose we have a planar robotic arm with two links, L1 and L2, and two revolute joints, θ1 and θ2. The lengths of the links are L1 = 1 meter and L2 = 0.5 meters, and the joint angles are θ1 = 45 degrees and θ2 = 30 degrees. Our goal is to find the position (x, y) of the end effector in a 2D Cartesian coordinate system.

First, we need to convert the joint angles from degrees to radians: θ1 = 45° * (π/180) ≈ 0.785 radians θ2 = 30° * (π/180) ≈ 0.524 radians

Now, we can use forward kinematics to find the position of the end effector (x, y):

x = L1 * cos(θ1) + L2 * cos(θ1 + θ2)
x = 1 * cos(0.785) + 0.5 * cos(0.785 + 0.524)
x ≈ 0.83679

y = L1 * sin(θ1) + L2 * sin(θ1 + θ2)
y = 1 * sin(0.785) + 0.5 * sin(0.785 + 0.524)
y ≈ 1.18978

So, the position of the end effector in the 2D Cartesian coordinate system is approximately (1.207, 1.032).

In this example, we used kinematics, specifically forward kinematics, to find the position of a robotic arm’s end effector given the lengths of the links and the joint angles. This is a typical problem in robotics and demonstrates how kinematics can be applied in computer engineering.

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