Introduction
Motion in a Straight Line is an important topic of physics as it helps to understand different types of motion of an object, like curvilinear motion and motion in multiple dimensions. Motion in a Straight Line Class 11 Physics Chapter 2 Notes include a brief description of the concept of kinematics of an object, speed, velocity, and acceleration.
What is Motion in a Straight Line?
Motion in a Straight Line refers to the movement of an object along a straight path, and it is also called rectilinear motion. It is a one-dimensional motion. This type of motion is of two types: Uniform Motion and Non-Uniform Motion.
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Uniform Motion in a Straight Line
Uniform Motion describes an object moving in a straight line with a constant velocity. An object in uniform motion covers equal distances in equal time intervals.
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Non-Uniform Motion in a Straight Line
An object has Non-Uniform Motion when its velocity changes with time. In this motion, an object does not cover equal distances in equal time intervals.
Path Length
Path Length means the total distance of the actual path travelled by an object in motion. The distance covered by the object from the initial and final positions is the total path length.
Displacement
Displacement refers to the change of the position of an object in a particular direction during a particular time. The direction and distance between the initial and final locations of the object.
Difference between Distance and Displacement –
| Distance | Displacement |
| 1. Length of the actual path between the initial and final position | 1. Length of the shortest path between the initial and final position. |
| 2. Scalar quantity | 2. Vector quantity |
| 3. Distance can never be zero or negative; it is always positive | 3. It can be positive, negative, or zero. |
Difference between Speed and Velocity –
| Speed | Velocity |
| 1. It refers to the total length of the path travelled divided by the total time during which motion occurs. | 1. It means the change in position divided by the time during which the displacement occurs. |
| 2. Scalar quantity | 2. Vector quantity |
| 3. It is always positive | 3. It can be positive, negative, or zero. |
Average speed and Average velocity
Average speed can be calculated by dividing the total path length by the total time duration the motion occurs.
- Average speed = Total distance / total time
Average velocity refers to the change or displacement of position divided by the total time. The SI unit of velocity is m/s.
- Average velocity = Total displacement / total time
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Instantaneous speed and Instantaneous velocity
Instantaneous speed can be defined as the magnitude of velocity.
- The SI unit is m/s.
Instantaneous velocity is the limit of the average velocity as the time interval t becomes infinitesimally small. It is the velocity at any instant of time or any point of the path.
- The SI unit is m/s.
Acceleration
Acceleration refers to the rate at which velocity changes with time. It is a vector quantity.
Uniform Acceleration
An object with an equal change in velocity in equal time intervals is called Uniform Acceleration.
Average and Instantaneous Acceleration
When a change in velocity is divided by the time it occurs, it is called Average Acceleration.
Instantaneous Acceleration is the limit of Average Acceleration as the time interval t goes to zero.
Relative Velocity
Relative Velocity of an object to another is the time rate at which the object changes its position with respect to another.
- The relative velocity of two objects moving in the same direction is calculated by the difference in speed between the objects.
- The relative velocity of two objects moving in opposite directions is the sum of the speeds of the objects.
Important Table —
| Physical quantity | Symbol | Dimensions | Units |
| Path Length | [L] | m | |
| Displacement | Δx | [L] | m |
| Velocity
i) Average ii) Instantaneous |
v
v |
[LT-1] | ms-1 |
| Speed
i)Average ii) Instantaneous |
LT-1 | ms-1 | |
| Acceleration
i)Average ii) Instantaneous |
a
a |
[LT-2] | ms-1 |
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Conclusion
Motion in a Straight Line Class 11 Physics Chapter 2 Notes are crucial as they help to understand how any object moves in a straight line. This note emphasizes the concept of speed, velocity, and acceleration of a moving object. The experts of Learn Physics with Ease summaries the important formulas and main points of this chapter to revise quickly by the students before the exam in their study materials.
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