Motion in a Straight line Class 11 — Completes Notes With PDF

Motion in a Straight line Class 11 Notes

Let’s start the introduction of Motion in a straight line chapter. In this chapter, first, learn about the difference between rest and motion then types of motion, and all other concepts related to this chapter. Read this article and solve all-important questions related to motion in a straight line class 11.

Mechanics

It is the branch of physics that deals with the conditions of rest or motion of the material objects around us.

Rest

If an object does not change its position with respect to its surroundings with time, then it is known as rest.

Motion

If an object changes its position with respect to its surroundings with time, then it is known as motion.

Types of Motion

1. Uniform Motion in a Straight Line

An object is said to be uniform motion if it covers equal distances in equal interval of time, however small these time intervals may be in the fixed direction.

Important facts of Uniform Motion in a straight line

• For an object is uniform motion, no force is required to maintain its motion.
• The velocity in uniform motion does not depend on the choice of origin.
• The velocity in uniform motion does not depend on the choice of the time interval (t2-t1).

1. Non-uniform motion in a straight line

An object is said to be in non-uniform motion if its velocity changes with time.

Point object

If the position of the object changes by distances much greater than its own size in a reasonable duration of time, then the object may be regarded as a point object.

Examples: Earth can be regarded as a point object for studying its motion around the sun.

Types of motion

1. One dimensional motion

If only one out of three coordinates specifying the position of the object changes w.r.t. (with respect to) time, then the motion is known as one-dimensional motion. It is also called rectilinear motion.

Example:-

• The motion of a freely falling body.
• The motion of a train along a straight track.

1. Two-dimensional motion

If only two out of three coordinates specifying the position of the object change w.r.t. (with respect to) time, then the motion is known as two-dimensional motions.

Example:-

• The motion of planets around the sun.
• A car moving along a zigzag path on a level road.

1. Three-dimensional motion

If all the three coordinates specifying the position of the object change w.r.t. (with respect to) time, then the motion is known as the three-dimensional motion.

Example:-

• The motion of aeroplane in space.
• A kite flying a windy day.

Distance

The length of the actual path travelled by an object is known as distance.

• SI unit of distance = metre (m)
• The CGS unit of distanced = centimetre (cm)
• It is a scalar quantity because it has only magnitude and no direction.
• It can never be zero or negative during the motion of an object.

Displacement

The displacement of an object is the change in the position of an object in a fixed direction.

• Its SI unit is metre.
• The CGS unit of displacement = centimetre (cm)
• Displacement is a vector quantity because it has both magnitude and direction.
• The displacement of a body in a given time can be positive, zero or negative.

Properties of Displacement

• Displacement is not dependent on the choice of the origin (O) of the position coordinates.
• The magnitude of the displacement of an object between two positions gives the shortest distance between these positions.
• Displacement of an object between two given positions is independent of the actual path followed by the object is moving from one position to another.
• The actual distance travelled by an object in a given time interval is greater than or equal to the magnitude of the displacement.
• The displacement of an object between two positions does not give any information regarding the shape of the actual path followed by the object between these two positions.

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