Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Mechanics → Motion ↓


Distance and displacement


Introduction

In physics, understanding motion is crucial to explaining how objects move. Two important concepts when studying motion are distance and displacement. Although they may seem similar, they have different meanings and applications. This comprehensive guide will explain both concepts, provide examples, and help differentiate them. Let's dive deeper into the fundamentals of motion in mechanics!

What is the distance?

Distance is a scalar quantity that tells “how much distance an object has covered during its motion”. In simple words, it is the total path length covered by the object, irrespective of the direction.

Distance characteristics

  • Distance is always positive or zero.
  • It is scalar, that is, it has only magnitude and no direction.
  • The SI unit of distance is meter (m).

Distance examples

Imagine you are walking in a park. You start from point A, walk to point B and then to point C. If the distance from A to B is 50 m and the distance from B to C is 30 m, the total distance you have walked is:

Total Distance = Distance AB + Distance BC = 50 meters + 30 meters = 80 meters

Visual representation

A B C

What is displacement?

Displacement is a vector quantity that refers to the "change in position" of an object. It is a straight line from the object's starting point to the final position, regardless of direction.

Displacement characteristics

  • Displacement can be positive, negative or zero.
  • It is a vector, that is, it has both magnitude and direction.
  • The shortest distance between the initial and final points.
  • The SI unit of displacement is metre (m).

Examples of displacement

Using the same park example: If your starting point (A) and ending point (C) are 70 meters apart in a straight line, the displacement is simply:

Displacement = Final Position - Initial Position = AC (straight line) = 70 meters

Visual representation

A C Displacement

Main differences between distance and displacement

Understanding the difference between distance and displacement can help make these concepts more clear.

Aspect Distance Displacement
Type Scalar quantity Vector quantity
Magnitude Always positive or zero Positive, negative or zero
Direction No direction The direction is
Path Actual travel path Shortest path
SI unit Meter (m) Meter (m)

Distance and displacement in everyday scenarios

Let us look at some real-life situations to understand these concepts better.

Example 1: Running track

Consider a runner on a 400 m circular track. If the runner completes a full lap and ends at the starting point, the total distance is 400 m. However, the displacement is zero because there is no overall change in position.

Example 2: City block

Imagine you are walking in a square pattern around city blocks. If you walk 3 blocks east, then 3 blocks south, 3 blocks west, and finally 3 blocks north, you are back at your starting point. Your total distance is 12 blocks, but your displacement is zero.

Mathematical calculation of displacement

Displacement is calculated using vectors. Vectors have both magnitude and direction, which makes them suitable for describing displacement.

If the initial and final positions are known, the displacement vector can be calculated as follows:

Displacement (Δx) = Final Position (x₂) - Initial Position (x₁)

Here's an example:

Suppose you are at position (3, 4) and move to position (7, 1), then:

Δx = (7 - 3) = 4 Δy = (1 - 4) = -3 Displacement = √(Δx² + Δy²) = √(4² + (-3)²) = √(16 + 9) = √25 = 5 units

Summary

  • Distance measures how much distance the object has covered.
  • Displacement tells us how far an object is from its original position; it is the change in the object's position.
  • Distance is scalar, relating only to magnitude, while displacement is vector, relating magnitude and direction.
  • It is important to understand these concepts in order to accurately analyze and describe motion.

Conclusion

Distance and displacement are both fundamental concepts in physics, especially in the study of motion. They are essential for solving many practical problems involving moving objects. While distance tells you the extent of the path traveled, displacement tells you the net change in position between two points in space. Remembering the key differences between these two will strengthen your understanding of motion in the physical world.


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Distance and displacement

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