Motion and Rest:

  • Rest and Motion: Objects around us are either at rest (not moving) or in motion (moving). Examples include birds flying, cars moving, blood flowing, and even atoms and planets.
  • Perception of Motion: We usually see motion when an object’s position changes with time. However, sometimes we can infer motion indirectly, like by observing how dust moves when the air flows.
  • Relative Motion: Motion can appear different to different observers. For instance, to someone on a bus, roadside trees seem to move backward, while the person standing on the roadside sees the bus and its passengers as moving. This is due to relative motion — the perception of movement depends on your point of view.

Types of Motion:

  • Linear Motion: When an object moves along a straight path. For example, an object moves from position O to position A, then back from A to O. Here, we can measure both the distance (total path length) and displacement (shortest distance between initial and final positions).
  • Distance vs Displacement:
    • Distance is the total path traveled (always positive and includes direction).
    • Displacement is the shortest straight-line distance from the start to the end point, and it can be zero even if the distance covered is non-zero (e.g., moving in a circle and ending up where you started).

Uniform vs Non-Uniform Motion:

  • Uniform Motion: If an object covers equal distances in equal time intervals (e.g., moving 5 meters every second), its motion is called uniform motion. Example: A car driving at a constant speed.
  • Non-Uniform Motion: When an object covers unequal distances in equal time intervals (e.g., a car moving faster and slower at different times), it is in non-uniform motion.

Speed and Velocity:

  • Speed: The rate of motion, calculated as distance divided by time. It is a scalar quantity (only magnitude, no direction).
    • Formula: Speed = Distance / Time
    • SI unit: m/s (meters per second).
  • Velocity: Like speed but with direction. If an object moves in a specific direction, its velocity is described by both speed and direction.
    • Formula: Velocity = Displacement / Time
    • SI unit: m/s.
  • Average Speed and Average Velocity:
    • If an object’s motion is not uniform, we calculate average speed (total distance divided by total time).
    • Average velocity is the displacement divided by the time.

Acceleration:

  • Acceleration: Measures how much the velocity of an object changes in a given time. If an object speeds up, it has positive acceleration, and if it slows down, it has negative acceleration (deceleration).
    • Formula: Acceleration = Change in velocity / Time taken
    • SI unit: m/s².
  • Uniform vs Non-Uniform Acceleration: If the velocity increases or decreases by equal amounts in equal time intervals, the object experiences uniform acceleration (e.g., a freely falling object). If the change in velocity is unequal over equal time intervals, the object has non-uniform acceleration.

Example for Calculation:

  • Car Travel Example: If a car moves from point A to point B, and we know the distance and time, we can calculate the car’s average speed using the formula:
    • Average speed = Total distance / Total time.
  • Velocity and Displacement: If an object moves from point A to point B, its displacement is the straight-line distance between the two points, which is different from the total distance covered (the actual path taken).

Graphical Representation of Motion: Notes

Graphs in Motion

  • Graphs are helpful to present information clearly, such as the run rate in cricket or solving linear equations.
  • For motion, graphs show how one physical quantity (like distance or velocity) changes with another (like time).

Distance-Time Graphs

  • A distance-time graph shows how an object’s position changes with time.
  • Time is plotted on the x-axis and distance on the y-axis.

Uniform Speed (Constant Speed):

  • If an object moves with uniform speed, it covers equal distances in equal intervals of time.
  • The distance-time graph is a straight line (constant slope), indicating uniform motion.
  • You can calculate the speed (or velocity) by finding the slope of the graph:
    • Speed=Change in distance/Change in time​

Non-Uniform Speed:

  • If the speed is changing (acceleration or deceleration), the distance-time graph will not be a straight line.
  • For example, if a car accelerates, the graph curves upward.

Velocity-Time Graphs

  • A velocity-time graph shows how an object’s velocity changes over time.
  • Time is on the x-axis and velocity on the y-axis.

Uniform Velocity (Constant Speed):

  • If the object moves at a constant velocity, the graph will be a horizontal line.

Displacement from Velocity-Time Graph:

  • The area under the velocity-time graph gives the displacement (distance covered).

Uniformly Accelerated Motion

  • When an object accelerates at a constant rate, the velocity-time graph is a straight line.
  • The area under this graph gives the displacement.

For example, if a car accelerates uniformly, the area under the graph can be split into a rectangle (for the constant velocity) and a triangle (for the acceleration part).

Equations of Motion

  • For motion with uniform acceleration, three key equations describe the relationships between velocity, distance, and time:
    1. v= u+at
    2. s= ut+1/2at2
    3. 2as= v2−u2

Where:

  • u = initial velocity
  • v = final velocity
  • a = acceleration
  • t = time
  • s = distance

Example Applications:

  • A train starts from rest and attains a velocity of 72 km/h in 5 minutes. Using the equations of motion, you can calculate the acceleration and distance covered during this time.
  • A car stops after applying the brakes, with a deceleration of 6 m/s². By applying the equations, you can calculate the stopping distance.

Uniform Circular Motion

  • In uniform circular motion, an object moves in a circle with constant speed. Although the speed is constant, the direction of motion changes continuously.
  • The motion is accelerated because of the continuous change in direction.
  • The speed in circular motion is calculated using:
    • v= 2πr​/T

Where rrr is the radius of the circle and T is the time taken for one complete revolution.

Summary:

  • Motion is the change in position of an object.
  • Uniform motion means constant speed or velocity, represented by straight-line graphs.
  • Non-uniform motion involves changing speed or velocity, represented by curved graphs.
  • Acceleration is the change in velocity over time.
  • The area under a velocity-time graph represents the displacement.
  • The motion of an object with uniform acceleration can be described using the three key equations of motion.

THESE ALL ARE THE NOTES OF CHAPTER 7 SCIENCE. AND AFTER SOME TIME YOU GET IMPORTANT QUESTIONS HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊