C
CraftExam
high importancemedium8 min

Uniform Circular Motion

Uniform circular motion is motion along a circular path with constant speed, while the direction of velocity changes continuously.

Practice This Concept

Learn the concept

Student-friendly explanation

In circular motion, the object covers equal distances in equal intervals of time if speed is constant. Still, velocity changes because its direction is different at different points of the circle. This means the object is accelerating even at constant speed.

How to write this in exams

  1. 1

    Start with the exact idea

    Uniform circular motion is motion along a circular path with constant speed, while the direction of velocity changes continuously.

  2. 2

    Then show how to use it

    Check if path is circular. Check if speed is constant. State that direction changes at every point. If asked for speed in one round, use 2πr divided by time period.

  3. 3

    Add one concrete example

    A stone tied to a string and whirled at steady speed is in uniform circular motion.

  4. 4

    Avoid this incomplete answer

    Saying acceleration is zero because speed is constant is wrong because velocity also depends on direction.

Definition

Uniform circular motion is motion along a circular path with constant speed, while the direction of velocity changes continuously.

Example

A stone tied to a string and whirled at steady speed is in uniform circular motion.

Rule to remember

For one complete round, speed = circumference / time = 2πr / T, where r is radius and T is time period. Velocity direction is tangent to the circle at each point.

Memory hook

Same speed, new direction, changing velocity.

Examples and method

Worked example

A toy car moves around a circular track of radius 7 m in 11 s. Distance in one round = 2πr = 44 m approximately. Speed = 44/11 = 4 m/s, but its velocity changes at every point because direction changes.

Method to apply

Check if path is circular. Check if speed is constant. State that direction changes at every point. If asked for speed in one round, use 2πr divided by time period.

Diagram support

Draw a circle with velocity arrows tangential at different points and an inward direction change shown toward the centre.

How CBSE asks it

Questions may ask why constant-speed circular motion is accelerated or ask for speed using 2πr/T.

Avoid common mistakes

Common confusion

Students often think constant speed means zero acceleration in all cases, but direction change also changes velocity.

Common wrong answer

Saying acceleration is zero because speed is constant is wrong because velocity also depends on direction.

Exam tip

For circular motion, mention both points: speed is constant, but velocity changes because direction changes.

Quick check

Why is uniform circular motion called accelerated motion?

Uniform circular motion is called accelerated motion because velocity changes continuously due to change in direction, even though speed remains constant.

Answer writing and exam use

1-mark answer

Uniform circular motion is motion along a circular path with constant speed, while the direction of velocity changes continuously.

2-mark answer

Uniform circular motion is motion along a circular path with constant speed, while the direction of velocity changes continuously. For one complete round, speed = circumference / time = 2πr / T, where r is radius and T is time period. Velocity direction is tangent to the circle at each point. A stone tied to a string and whirled at steady speed is in uniform circular motion.

3-mark answer

In circular motion, the object covers equal distances in equal intervals of time if speed is constant. Still, velocity changes because its direction is different at different points of the circle. This means the object is accelerating even at constant speed. For one complete round, speed = circumference / time = 2πr / T, where r is radius and T is time period. Velocity direction is tangent to the circle at each point. A toy car moves around a circular track of radius 7 m in 11 s. Distance in one round = 2πr = 44 m approximately. Speed = 44/11 = 4 m/s, but its velocity changes at every point because direction changes. Questions may ask why constant-speed circular motion is accelerated or ask for speed using 2πr/T. Saying acceleration is zero because speed is constant is wrong because velocity also depends on direction.
MCQ Quiz

Practice this concept with focused MCQs

Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.

10 MCQs5 MinutesInstant Results
Practice This Concept

Help improve this page

Found something confusing, incorrect, or missing?

Practice This Concept