Motion in a Straight Line - Lesson 1 Notes

Chapter 1: Motion in a Straight Line

Lesson 1: Rest and Motion

Competency

  • Investigate motion of an object in terms of position, velocity, and acceleration with respect to time.

  • Apply mathematical relations to solve problems numerically and graphically.

Lesson Objectives

  • Explain rest and motion, position, and path length of an object.

Scope

  • Rest and motion

  • Position and path length

Mechanics

Mechanics is the branch of physics that deals with the study of motion. It is divided into three main areas:

  • Statics: Deals with objects at rest/equilibrium.

  • Kinematics: Deals with simple descriptions of motion only.

  • Dynamics: Deals with the description of motion and its cause.

Rest and Motion

Rest

An object is said to be at rest when it does not change its position with respect to its surroundings (frame of reference).

Motion

An object is said to be in motion when it changes its position with respect to its surroundings.

Example:

A teacher walking out of the classroom with a book:

  • With respect to the teacher, the book is at rest.

  • With respect to a student in the classroom, the book is in motion.

Position and Reference Frame

Position

Location of an object relative to some reference point (origin or zero of an axis).

Frame of Reference

When the position of an object is determined with respect to a three-dimensional coordinate system along with time, it is known as a frame of reference.

Relative Motion

For example, the driver of a moving car is in motion with respect to an observer standing on the ground, whereas the same driver is at rest with respect to a passenger in the car. Rest and motion are dependent on the observer.

Rest and Motion are Relative. The object in one situation may be at rest while the same object in another situation may be in motion.

Path Length

Definition

Path length in physics is the total distance traveled by an object, regardless of direction.

Properties

  • It is a scalar quantity (has only magnitude, no direction).

  • It is always positive.

Example

Sonam walks 3 m east, then 4 m north. The total path length is: 3 + 4 = 7 m, even though the displacement is just 5 m.

Reflection Questions

  • How can we determine whether an object is at rest or not?

  • Are all moving objects considered in motion?