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Motion and Time Class 7 Science Notes - Chapter 13

Motion and Time Class 7 Notes Science Chapter 13 

Preview of the chapter 

In our daily routines, we typically observe some objects at rest and others in motion, such as flying birds, swimming fish, planets orbiting the sun, etc. We frequently perceive an item to be in motion when its position changes over time. For example, when the position of an automobile changes over time, we remark that the car is moving or that it is in motion. 

An Introduction to Motion

Distance

  • The object's overall path traveled during the course of the time period in question is its distance.
  • The shortest path traveled by a moving object in the allotted amount of time is its displacement.
  • Distance=Speed×Time.
  • Typically, a distance unit is measured in length units like meters, kilometers, etc.

Introduction to motion

motion is the change in position of an object over time, and there are two types of motion: translational and rotational. It can be described using parameters such as speed, velocity, and acceleration, and is affected by different forces

Basics of Standard Units

Units and their standardization

  • The standard unit of distance is in metres.
  • The standard unit of time is in seconds (s).
  • The standard unit of speed is in metre per second (m/s).

Basics of Motion and Its Types

Types of motion

Types of motion are generally divided into 3. They are

  1. Translational Motion: This type of motion refers to the movement of an object from one point to another in a straight line or along a curved path. Examples of translational motion include a car moving along a road or a ball rolling down a slope.


  1. Rotational Motion: This type of motion occurs when an object rotates or spins around an axis or a fixed point. Examples of rotational motion include a spinning top or a rotating wheel.


  1. Vibrational Motion: This type of motion occurs when an object oscillates or vibrates about a fixed position. Examples of vibrational motion include a tuning fork vibrating or a guitar string vibrating.


Periodic or oscillatory motion

  • Periodic or oscillatory motion is a type of motion where an object moves back and forth repeatedly around a fixed position, returning to its initial position after each cycle. This type of motion is characterized by its amplitude, frequency, and period.
  • Examples of periodic or oscillatory motion include the motion of a pendulum, a mass attached to a spring, or a vibrating guitar string. These types of motion are common in many physical systems and are important in fields such as physics, engineering, and mathematics.

Oscillations of a simple pendulum

A simple pendulum is considered to have completed one oscillation when the bob goes from its mean position, B, to A and back to B, then from A to C and back to B.
The time period for a basic pendulum is the total amount of time needed for it to complete one oscillation.

Time and Speed

The speed of an object is defined as the distance it travels in a unit of time (either in an hour, a minute, or a second). A fast-moving object has a high speed, while a slow-moving object is said to have a low speed. We can determine which bus is slower if we know how far two buses travel in an hour. Therefore, Speed = DistanceTraveledTimeTaken can be used to calculate an object's speed, for example. A car's speed is determined by Speed = 100km2h = 50 km/h if it covers a distance of 100 km in two hours.

Uniform and Non-Uniform Motion

1. Uniform motion: When an object moves in a straight path at a consistent speed, it is said to be in uniform motion.
For example, consider a car driving in a straight line at a constant speed.

2. Non-uniform motion: Uniform motion occurs when an item moving in a straight line varies its speed with respect to time.
As an example, consider train motion.

Measurement of Time

Time is a duration or moment in which things occur. Ancient people did not have clocks or watches, so they used natural events to measure time. For example, the sun rises every day in the morning, so the time between one sunrise and the next was known as a day and the time from one full moon to the next was known as a month.

Units of Time

Time is typically measured in seconds, minutes, and hours.

Units of Speed

  • Speed = total distance traveled in the time interval.
  • Speed is commonly measured in metres per second (m/s) and kilometers per hour (km/h).

Speedometer and Odometer

  • The speedometer directly measures the vehicle's speed in kilometres per hour (km/h).
  • An odometer measures the distance traveled by a vehicle in kilometres (km).

Visualizing Motion

Distance-time graph

  • The graph with time on the x-axis and distance on the y-axis is called a distance-time graph.
  • The speed of an object is determined by the slope of a distance-time graph.


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