Preparing with the help of Class 9 Physics Motion Notes can help in better understanding of Class 9 Physics syllabus. Motion is the change in position of an object with respect to time and a reference point.
Here the Types of Motion Class 9, differences between distance and displacement, formulas for speed, velocity, and acceleration, and equations of motion are explained in a structured manner.
It also includes Motion Class 9 Numericals for practice and a Notes of Motion Class 9 PDF for better understanding.
What is Motion?
In physics, motion is defined as a change in the position of an object with respect to time and a reference point (origin). If an object’s position does not change, it is said to be at rest.
Types of Motion Class 9
Motion can be categorized based on the path taken by the object:
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Uniform Motion: When an object covers equal distances in equal intervals of time.
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Non-Uniform Motion: When an object covers unequal distances in equal intervals of time (e.g., a car moving in heavy traffic).
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Linear Motion: Motion in a straight line.
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Circular Motion: Motion along a circular path.
Scalar vs Vector Quantities
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Scalar Quantity: Has only magnitude (e.g., Distance, Speed).
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Vector Quantity: Has both magnitude and direction (e.g., Displacement, Velocity, Acceleration).
Distance and Displacement
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Distance: The total path length traveled by an object. It is always positive. For example, imagine you walk from your house to a shop 2 km away, then walk back 1 km toward your house. You’ve covered a total Distance of 3 km. It is a Scalar quantity (it only cares about "how much" you moved).
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Displacement: The shortest straight-line distance between the initial and final positions. It can be zero if the object returns to its starting point. In the same example, you are now only 1 km away from your house (the starting point). So, your Displacement is 1 km. It is a Vector quantity (it cares about "how much" and "in which direction").
Difference Between Distance and Displacement
Nature:
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Distance is a scalar quantity (only magnitude).
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Displacement is a vector quantity (magnitude and direction).
Measurement:
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Distance is the total path length covered.
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Displacement is the shortest path between two points.
Value:
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Distance is always positive and never zero if there is any movement.
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Displacement can be positive, negative, or zero.
Example:
If you walk in a circular path and return to your starting point, the distance covered is the circumference of the circle, while the displacement is zero.
Speed and Velocity
Speed is the rate of change of distance.
Speed = Distance/Time
Velocity is speed in a specific direction.
Velocity = Displacement/Time
Average Speed: The total distance traveled divided by the total time taken.
Average Speed = Total Distance/Total Time
Acceleration: The Rate of Change
Acceleration (a) is defined as the rate of change of velocity.
Where:
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a = acceleration, u = initial velocity, v = final velocity, T = time taken
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SI Unit: meter per second square
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Retardation: Negative acceleration (when an object slows down).
Equations of Motion (Graphical Method)
There are three fundamental equations for objects moving with uniform acceleration:
Uniform Circular Motion
When an object moves in a circular path with uniform speed, its velocity changes at every point because the direction changes. This is called accelerated motion.
Where:
𝑟= radius of the circular path
𝑡= time for one complete revolution
Motion Class 9 Numericals
To truly master Class 9 Physics Motion Notes, you must practice numerical problems.
Example 1: An object travels 16m in 4s and then another 16m in 2s. What is the average speed of the object?
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Solution:
Example 2: A bus decreases its speed from 80 km/h to 60 km/h in 5s. Find the acceleration.
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Solution:
Class 9 Physics Motion Notes PDF
The Class 9 Physics Motion Notes PDF provides all essential concepts in a concise and easy-to-understand format. It includes definitions and key concepts such as motion, distance, displacement, speed, velocity, and acceleration.
The PDF also explains the types of motion in Class 9, including linear, circular, uniform, and non-uniform motion, with clear examples. All equations of motion are provided along with solved examples to help students apply them effectively.
Graphical Representation of Motion
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Distance-Time Graph: The slope gives the Speed.
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Straight line = Uniform speed.
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Curved line = Non-uniform speed.
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Velocity-Time Graph: * The slope gives the Acceleration.
The area under the graph gives the Displacement.
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