Class 9th physics motion Notes ncert For Upsc

Class 9th physics motion Notes ncert In very very very Easy English words In Minimum 600 words according to upsc syllabus 

Class 9th physics motion Notes ncert For Upsc 

UPSC Preliminary Examination Paper GS-1

Subject: General Science 

Chapter: Motion - Class 9th Physics 📝 Notes

Introduction to Motion

Motion is a fundamental concept in physics that refers to the change in position of an object with respect to time. If an object changes its position over time, it is said to be in motion. Understanding motion helps us comprehend how things move and behave in our world.

Types of Motion

There are different types of motion depending on the path taken by the object:

1. Rectilinear Motion: This is the motion along a straight line. For example, a car moving on a straight road.

2. Circular Motion: When an object moves along a circular path, it is called circular motion. An example is the motion of the Earth around the Sun.

3. Periodic Motion: Motion that repeats itself after a fixed interval of time is called periodic motion. A pendulum's swing is an example.

4. Rotational Motion: When an object spins around its own axis, it is called rotational motion. The rotation of the Earth on its axis is a good example.

Concepts of Distance and Displacement

• Distance: Distance is the total path covered by an object during its motion. It is a scalar quantity, which means it only has magnitude and no direction. For example, if you walk 3 km to the north and then 4 km to the east, the total distance traveled is 7 km.

• Displacement: Displacement is the shortest straight line distance between the starting and ending point. It is a vector quantity, meaning it has both magnitude and direction. In the previous example, the displacement would be the straight line distance from your starting point to your final position.

Speed and Velocity

• Speed: Speed is the rate at which an object covers distance. It is a scalar quantity. Speed is given by the formula:

  $$\text{Speed} = \frac{\text{Distance}}{\text{Time}}$$

  For example, if a car travels 100 km in 2 hours, its speed is 50 km/h.

• Velocity: Velocity is the speed of an object in a specific direction. It is a vector quantity. If the direction of an object's motion changes, its velocity changes even if its speed remains the same. The formula for velocity is:

  $$$$Velocity=DisplacementTime​

Acceleration

Acceleration refers to the rate of change of velocity with time. It tells us how quickly an object is speeding up or slowing down. The formula for acceleration is:

$$\text{Acceleration} = \frac{\text{Change in Velocity}}{\text{Time Taken}}$$

​

Acceleration can be positive (speeding up) or negative (slowing down), also known as deceleration.

Graphical Representation of Motion

In physics, graphs are used to represent motion visually:

1. Distance-Time Graph: This graph shows how the distance of an object changes with time. A straight line indicates constant speed, while a curved line shows acceleration.

2. Velocity-Time Graph: This graph indicates how velocity changes over time. The slope of the line on a velocity-time graph gives acceleration.

Uniform and Non-Uniform Motion

• Uniform Motion: When an object moves at a constant speed in a straight line, it is in uniform motion. In this case, the object covers equal distances in equal intervals of time.

• Non-Uniform Motion: When an object’s speed changes, it is in non-uniform motion. Here, the object covers unequal distances in equal intervals of time.

Equations of Motion

The equations of motion relate velocity, acceleration, time, and displacement:

1. First Equation:

   $$v = u + at$$
   

   Where:

   • $v$ is the final velocity
   • $u$ is the initial velocity
   • $a$ is acceleration
   • $t$ is time

2. Second Equation:

   $$s=ut+\frac{1}{2}a{t}^2$$

   Where:

   • $s$ is the displacement

3. Third Equation:

   $$v^2 = u^2 + 2as$$
   

These equations help solve various problems related to motion.

Important Concepts

• Inertia: Inertia is the tendency of an object to resist any change in its state of motion. An object at rest stays at rest, and an object in motion stays in motion unless acted upon by an external force.

• Relative Motion: Motion is always measured relative to something else. For example, when you are sitting in a moving bus, you are at rest relative to the bus but in motion relative to the ground.

Summary

Motion is a crucial concept in physics that describes the change in an object’s position over time. Understanding the types of motion, speed, velocity, acceleration, and equations of motion helps in solving real-world problems and is fundamental to the study of physics. By grasping these basics, students can build a strong foundation for more advanced topics in physics.