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 ↓


Speed and Velocity


When we talk about motion in physics, the two most basic concepts are speed and velocity. They help us understand how objects move around us. Although they may seem similar, speed and velocity have different meanings and implications in physics.

Understanding momentum

Speed is a measure of how fast an object is moving. It is a scalar quantity, meaning it has only magnitude and no direction. Think of it as the rate at which an object travels a distance. When you look at the speedometer in a car, you are looking at the speed of the car at that particular moment.

Formula of speed

Speed = Distance / Time

This formula tells us that speed is the total distance traveled divided by the total time taken to travel that distance. For example, if a car travels 150 kilometers in 3 hours, then the speed of the car is:

Speed = 150 km / 3 hrs = 50 km/hr

Here's a simple example to demonstrate motion:

0 Km 150 km 50 km/h

In this visualization, the red dot starts at 0 km and goes up to 150 km. The green line represents the speed, which is calculated as 50 kmph.

Examples of momentum

  • The speed of a runner jogging 5 km in 30 minutes is 10 km/hr.
  • The speed of a bicycle travelling 20 m in 4 sec is 5 m/s.
  • If a train covers a distance of 240 km in two hours at a constant speed, then its speed will be 120 km/hr.

Understanding velocity

Unlike speed, velocity is a vector quantity. This means it has both magnitude and direction. While speed tells us how fast something is moving, velocity tells us how fast something is moving and in what direction. For example, a car traveling at 60 km/h due north has a velocity of 60 km/h due north.

Velocity formula

Velocity = Displacement / Time

Displacement is the change in position of an object. It considers the initial and final points and the shortest path between them. If you start at point A, move to point B, and return to A, your displacement is zero, even though you have traveled some distance. Let's use an example to clarify:

Suppose a person walks 3 m east and then 4 m north, then the displacement can be seen as:

3 m 4 m Displacement

Here, the person walked along the path formed by the two black lines, yet the actual displacement is represented by the red line, which directly connects the start and end point.

Examples of velocity

  • The velocity of a bird flying 10 m in 2 sec towards east is 5 m/s east.
  • 50 km/hr south.
  • An aeroplane travels 600 km west in 2 hours, making a speed of 300 km/hr west.

Difference between speed and velocity

Although speed and velocity have similarities in describing motion, they also have clear differences:

Aspect Speed Velocity
Nature Scalar (magnitude only) Vector (magnitude and direction)
Dependency Distance travelled Displacement
Importance How fast something moves How fast something moves and where it goes

Analysis of motion

Let us consider a scenario where understanding both speed and velocity becomes useful:

Imagine you are on a circular track with a circumference of 400 m. If you complete one lap of the track in 100 seconds:

  • Your speed is the total distance (400 meters) divided by the time (100 seconds): 
    Speed = 400 m / 100 s = 4 m/s
  • However, your velocity depends on your starting and ending point. If you return to your starting point, your displacement is zero, making your velocity: 
    Velocity = 0 / 100 s = 0 m/s

This example highlights that the entire time you were moving, since you ended up back where you started, your displacement (and thus velocity) was effectively zero.

Practical considerations and applications

Understanding the difference between speed and velocity helps in real-world applications such as navigation, sports, and transportation. Here's how they relate in different contexts:

Navigation and GPS

GPS devices use velocity to provide directions. They calculate both your traveling speed and the direction you're headed. When your GPS says, "Drive north on Highway 1 at 60 km/h," it's telling you your speed, which helps you reach your destination efficiently.

Game

In sports such as baseball or track events, coaches focus on improving the athlete's speed. For a baseball pitcher, the speed of the ball is important, but the direction of the pitch is also important for a strike. Thus, understanding speed can improve performance.

Transportation

Transportation systems use both speed and velocity for safety and efficiency. Air traffic controllers need to know how fast and in what direction planes are moving to avoid collisions. Similarly, drivers adjust their speed and direction to obey traffic rules and reach a destination safely.

Conclusion

Understanding the concepts of speed and velocity is fundamental to delving deeper into physics and understanding motion. Although they can be used interchangeably in everyday language, recognizing their different definitions and roles is helpful in solving many real-world problems. Whether navigating roads, simulating sports dynamics, or ensuring safe airplane routes, speed and velocity provide key insights into organized, predictable motion.


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Speed and Velocity

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