Motion
Welcome to the chapter on Motion for Class 9. In this chapter, you will learn what motion is, types of motion, important terms like distance and displacement, speed and velocity, and how to solve problems related to motion. By the end of this chapter, you will understand how objects move and how to describe their movement using scientific terms and formulas.
Key Concepts
- Motion: Change in position of an object with time.
- Rest: When an object does not change its position with time.
- Distance: The total length of the path travelled by an object.
- Displacement: The shortest distance from the initial to the final position of an object.
- Speed: The rate at which an object covers distance (Speed = Distance / Time).
- Velocity: The rate at which an object changes its position (Velocity = Displacement / Time).
- Uniform Motion: When an object covers equal distances in equal intervals of time.
- Non-uniform Motion: When an object covers unequal distances in equal intervals of time.
Types of Motion
- Rectilinear Motion: Motion along a straight line (e.g., a car moving on a straight road).
- Circular Motion: Motion along a circular path (e.g., a fan blade).
- Periodic Motion: Motion that repeats after regular intervals (e.g., pendulum).
Distance and Displacement
- Distance is always positive and can be more than displacement.
- Displacement can be zero, positive, or negative.
- If you walk in a circle and return to the starting point, your displacement is zero but distance is the total path covered.
Speed and Velocity
- Speed is a scalar quantity (only magnitude).
- Velocity is a vector quantity (magnitude and direction).
- If direction changes, velocity changes even if speed is constant.
Formula for Speed: Speed = Distance / Time
Formula for Velocity: Velocity = Displacement / Time
Uniform and Non-uniform Motion
- Uniform motion: Speed remains constant.
- Non-uniform motion: Speed changes with time.
Practice Questions
- Define motion and rest.
- What is the difference between distance and displacement?
- A car travels 100 km in 2 hours. What is its speed?
- Give one example each of rectilinear, circular, and periodic motion.
- If a runner completes a round of a 400 m track and returns to the starting point, what is the displacement?
Challenge Yourself
- A bus moves 60 km north and then 80 km east. What is the total distance and displacement?
- Explain why velocity is a vector quantity but speed is not.
Did You Know?
- The fastest land animal is the cheetah, which can run up to 120 km/h!
- Earth moves around the sun in a nearly circular motion.
Glossary
- Scalar Quantity: Has only magnitude (e.g., speed).
- Vector Quantity: Has both magnitude and direction (e.g., velocity).
- Displacement: Shortest distance from start to end point.
Answers to Practice Questions
- Motion: Change in position with time. Rest: No change in position with time.
- Distance is the total path covered; displacement is the shortest distance between start and end points.
- Speed = 100 km / 2 h = 50 km/h
- Rectilinear: Car on a straight road. Circular: Fan blade. Periodic: Pendulum.
- Displacement is 0 m.
Understanding motion helps you describe and predict how things move in the world around you!