Describing Motion: Kinematics in One Dimension

Introduction to Kinematics

Kinematics is the branch of physics that describes the motion of objects without considering the causes of motion (forces). In one-dimensional kinematics, we focus on how an object's position changes with time along a straight line.

• Translational motion refers to movement along a straight path, as opposed to rotational or circular motion.

• The path along which an object moves is called the object's trajectory.

Types of Motion

• Linear motion: Movement along a straight line (e.g., a car driving on a straight road).

• Circular motion: Movement along a circular path (e.g., a Ferris wheel).

• Projectile motion: Curved path under gravity (e.g., a thrown ball).

Example: The image of a car with a parachute illustrates translational motion with velocity and acceleration vectors shown.

Motion Diagrams

Understanding Motion Diagrams

A motion diagram is a visual representation of an object's position at equally spaced instants of time. It helps us analyze how an object moves over time.

• A camera takes successive images (frames) at a fixed rate.

• Each image shows the object's position at a specific instant.

• The amount of time between each image is constant.

Interpreting Motion Diagrams

• If the spacing between positions is equal, the object moves at constant speed.

• If the spacing increases, the object is speeding up.

• If the spacing decreases, the object is slowing down.

Example: The diagram of a car at different positions along a road, with equal time intervals between images, shows uniform motion.

Kinematics - Description of Motion

Key Concepts

Kinematics focuses on the change of an object's position with time. The main quantities used to describe motion are:

• Position (x): The location of an object at a particular time.

• Displacement (Δx): The change in position; a vector quantity with magnitude and direction.

• Distance: The total length of the path traveled; a scalar quantity.

• Velocity (v): The rate of change of displacement; a vector quantity.

• Speed: The rate of change of distance; a scalar quantity.

• Acceleration (a): The rate of change of velocity; a vector quantity.

Scalar vs. Vector Quantities

• Scalars: Quantities described by magnitude only (e.g., distance, speed, mass, temperature).

• Vectors: Quantities described by both magnitude and direction (e.g., displacement, velocity, acceleration, force).

Example: The motion diagram and position graphs illustrate how position changes over time and how vectors are used to represent displacement and velocity.

Summary Table: Types of Motion

Additional info:

• In kinematics, we often use diagrams and graphs to visualize and analyze motion.

• Motion diagrams are foundational for understanding more complex motion in two or three dimensions.