Grade 10
  1. Mechanics  1.1. Dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration  1.1.6. Graphical representation of motion  1.1.7. Equations of motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Projectile motion  1.1.10. Relative speed  1.2. Dynamics  1.2.1. Newton's Laws of Motion  1.2.2. Inertia and mass  1.2.3. Force and its types  1.2.4. action and reaction force  1.2.5. Friction and its effects  1.2.6. Coefficient of friction  1.2.7. Circular motion  1.2.8. Centripetal force and centripetal acceleration  1.2.9. Momentum and Impulse  1.2.10. Conservation of momentum  1.2.11. Newton's third law and applications  1.3. Work, Energy and Power  1.3.1. Work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy  1.3.5. Mechanical energy  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.3.8. Renewable and non-renewable energy sources  1.4. Gravitational force  1.4.1. Newton's law of universal gravitation  1.4.2. Gravitational field and field strength  1.4.3. Acceleration due to gravity on different planets  1.4.4. Kepler's laws of planetary motion  1.4.5. Orbits and satellites  1.4.6. Weight and apparent weight  1.4.7. Gravitational potential energy
  2. Properties of matter  2.1. States of matter  2.1.1. Solid, liquid and gas  2.1.2. Molecular structure of matter  2.1.3. Intermolecular forces  2.1.4. Plasma and Bose–Einstein condensate  2.2. Pressure  2.2.1. Definition of Pressure  2.2.2. Pressure in liquids  2.2.3. Atmospheric pressure  2.2.4. Pascal's principle  2.2.5. Archimedes' Principle and Buoyancy  2.2.6. Surface tension and capillarity  2.3. Elasticity  2.3.1. Hooke's law  2.3.2. Stress and strain  2.3.3. Elastic Limit and Modulus of Elasticity  2.3.4. Applications of Elasticity
  3. Thermal physics  3.1. heat and temperature  3.1.1. Difference Between Heat and Temperature  3.1.2. Temperature scale  3.1.3. Thermal expansion  3.1.4. Thermal equilibrium  3.2. Heat transfer  3.2.1. Conductivity  3.2.2. Convection  3.2.3. Radiation  3.2.4. Insulation and its applications  3.3. Thermal properties of matter  3.3.1. Specific heat capacity  3.3.2. Latent heat and phase change  3.3.3. Boiling and Melting Point  3.3.4. Heat engines and refrigeration  3.4. Laws of Thermodynamics  3.4.1. Zeroth law of thermodynamics  3.4.2. First law of thermodynamics  3.4.3. Second law of thermodynamics  3.4.4. Carnot cycle
  4. Waves and optics  4.1. Nature and properties of waves  4.1.1. Types of waves in nature and properties of waves  4.1.2. Transverse and longitudinal waves  4.1.3. Wave parameters  4.1.4. Reflection and refraction of waves  4.1.5. Superposition and Interference  4.1.6. Standing Waves and Resonance  4.1.7. Doppler effect  4.2. Sound waves  4.2.1. Characteristics of sound waves  4.2.2. Speed of sound in different mediums  4.2.3. Applications of sound waves  4.2.4. Ultrasound and its uses  4.3. Light Waves and Optics  4.3.1. Nature of light  4.3.2. Reflection of light  4.3.3. Laws of reflection  4.3.4. Mirrors and Image Formation  4.3.5. Refraction of light  4.3.6. Snell's Law  4.3.7. Lenses and Image Formation  4.3.8. Total internal reflection and critical angle  4.3.9. Optical fibre  4.4. Optical Instruments  4.4.1. Microscope  4.4.2. Telescope  4.4.3. Human eye and vision defects  4.4.4. Camera and its working principle
  5. Electricity and Magnetism  5.1. Electrostatics  5.1.1. Electric charge and its properties  5.1.2. Conductors and Insulators  5.1.3. Coulomb's law  5.1.4. Electric field and field lines  5.1.5. Electric potential and potential difference  5.1.6. Capacitors and Capacitance  5.2. Current Electricity  5.2.1. Electric current and its measurement  5.2.2. Ohm's law  5.2.3. Resistance and resistivity  5.2.4. Series and Parallel Circuits  5.2.5. Electric power and energy  5.2.6. Kirchhoff's Laws  5.3. Magnetism and Electromagnetism  5.3.1. Magnetic field and field lines  5.3.2. Magnetic effects of electric current  5.3.3. Electromagnetic induction  5.3.4. Faraday's laws of electromagnetic induction  5.3.5. Transformers and Applications  5.3.6. AC and DC current
  6. Modern Physics  6.1. Nuclear physics  6.1.1. Structure of the atom  6.1.2. Bohr's atomic model  6.1.3. Electron Energy Levels  6.1.4. X-rays and applications  6.2. Radioactivity  6.2.1. Types of radiation  6.2.2. Half-life and radioactive decay  6.2.3. Nuclear reactions and applications  6.2.4. Fission and Fusion  6.3. Quantum physics  6.3.1. Wave–particle duality  6.3.2. Photoelectric effect  6.3.3. Energy quantization  6.3.4. Heisenberg's uncertainty principle
  7. Electronics and Communication  7.1. Semiconductors  7.1.1. Conductors, Insulators and Semiconductors  7.1.2. Diodes and their applications  7.1.3. Transistors and Logic Gates  7.1.4. LEDs and photodiodes  7.2. Communication Systems  7.2.1. Basics of communication  7.2.2. Analog and digital signals  7.2.3. Wireless and optical fibre communication  7.2.4. Radio Waves and Modulation

Grade 10 → Mechanics → Dynamics ↓


Relative speed


Kinematics is a fascinating branch of physics that focuses on understanding the motion of objects without considering the forces that cause the motion. An important concept in kinematics is relative motion. This idea helps us understand that motion is not absolute but depends on the point of view of the observer.

Basic concepts of relative motion

When we talk about motion, we usually refer to objects moving in different places. For example, imagine you are sitting in a car that is moving down the highway. When you sit still in the car, you may feel like you are at rest because the seat and the car around you move with you. In reality, both you and your seat are moving relative to, say, the trees or the road outside.

In other words, motion is always described relative to a frame of reference. If you change your position to another car or road, your view of the moving objects around you also changes. This is the essence of relative motion - how the position of an object changes in relation to other moving or stationary objects.

Using a reference frame

A frame of reference can be thought of as a system of objects that affects how we perceive motion. For example, a train is moving north at 50 km/h. Inside the train, a person walks south at 5 km/h. From the perspective of a person inside the train, that person appears to be moving south at 5 km/h. However, from an observer standing on the ground outside the train, that same person appears to be moving north at 45 km/h.

Frames of reference can be either stationary or moving. A fixed reference frame, such as the Earth, is stationary and does not move in the scenario under consideration. A moving frame of reference moves with the observer, such as the seat in a moving car.

Relative velocity

In the discussion of relative motion, velocity plays an important role. When considering two objects, the relative velocity is the velocity of one object relative to the other. Mathematically, the relative velocity of object A relative to object B, represented as vAB, is calculated as:

        vAB = vA - vB

Here:

  • vAB is the relative velocity of A with respect to B.
  • vA is the velocity of A relative to a stationary observer.
  • vB is the velocity of B relative to the same stationary observer.

Example: Cars on the highway

Suppose car A is travelling in the east direction at a speed of 60 km/h and car B is travelling in the east direction at a speed of 80 km/h. What is the relative velocity of car A with respect to car B?

Let's apply the formula:

        vAB = vA - vB = 60 km/h - 80 km/h = -20 km/h

The negative sign indicates that from the point of view of car B, car A is moving towards the west at a speed of 20 km/h.

Example: Walking on a moving platform

Imagine you are moving on a moving sidewalk at an airport. You move at a speed of 2 m/s relative to the ground. The moving sidewalk accelerates you at an additional speed of 1 m/s relative to the ground. How fast are you moving relative to a stationary observer standing on the ground?

To solve this:

        vperson, ground = vperson, sidewalk + vsidewalk, ground = 2 m/s + 1 m/s = 3 m/s

Therefore, you are moving at a speed of 3 m/s relative to the stationary observer.

Differentiating between relative and absolute speed

To understand relative motion, it is important to distinguish it from absolute motion. Absolute motion refers to the motion of an object relative to a universal reference point, often considered a fixed point in space. In contrast, relative motion refers to the motion of one object relative to another.

Examples: Space observation

If we watch the Earth move around the Sun, the motion looks different from different viewpoints. To an astronaut on the Moon, the Earth may appear to be moving in the sky in an apparent motion. At the same time, an observer on Mars may see the Earth and Mars moving in a completely different pattern due to their relative positions and paths.

Sun Earth Mars planet

This diagram shows a simplified representation of the positions of the Sun, Earth and Mars, and illustrates how the changing positions of the planets can affect activities seen from different viewpoints.

Vectors and relative motion

Relative motion in dynamics often involves vector analysis. Vectors represent quantities that have both magnitude and direction, such as velocity and displacement. Understanding vectors provides a broader perspective on relative motion that would be impossible using only scalar quantities.

Example: Airplane and air

Suppose an airplane is flying in the north direction at a speed of 100 m/s, while the wind is blowing from west to east at a speed of 20 m/s. We can determine the actual speed of the plane relative to the ground using vector addition.

Airplane (100 m/s) Wind (20 m/s) Resultant

The actual ground velocity can be calculated using vector addition:

        vresultant = sqrt((100 m/s)2 + (20 m/s)2)
    
        vresultant ≈ 101.98 m/s

Here, the motion of the airplane as seen from the ground, taking into account both its velocity and the speed of the wind, forms the hypotenuse of a right triangle.

Practical applications of relative motion

Understanding relative motion is very important in everyday life and technology. Engineers, sailors, scientists, and even athletes must understand this concept.

Applications: GPS & navigation

Global Positioning System (GPS) devices rely on the principles of relative motion. These devices calculate position by measuring the relative speed between satellites in space and your location on Earth.

Applications: Games

In sports such as tennis or cricket, players constantly adjust their movements based on the speed of the ball and other players. Understanding and anticipating relative speeds can give athletes a competitive edge.

Conclusion on relative speed

In short, relative speed is an insightful concept that shows us that speed is not a single or absolute phenomenon, but instead depends on observing and interpreting the conditions of the surrounding environment. Speed can change significantly when viewed from different frames of reference, and this understanding helps us understand, evaluate, and appreciate real-world and cosmic motions.

This concept encourages us to look beyond surface-level observations and understand the intricate dance of nature, giving context and meaning to even the simplest or most complex movements we encounter.


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Relative speed

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