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 → Gravitational force ↓


Acceleration due to gravity


The concept of "acceleration due to gravity" is fundamental in physics, specifically in the study of mechanics and gravity. It refers to the acceleration experienced by an object due to the gravitational pull of the Earth. For this exploration, we will explain this concept in a way that is simple and easy to understand.

What is acceleration?

Before we learn about acceleration due to gravity, let us first understand what acceleration means. Acceleration is the rate at which the velocity of an object changes with time. When an object speeds up, slows down or changes direction, it is accelerating.

For example, if a car accelerates from 0 km/h to 60 km/h in 10 seconds, then the car is accelerating.

Introduction to gravitation

Gravity is a force that attracts two bodies towards each other. It is the reason we remain stationary on Earth and it is the reason objects fall when they fall. Sir Isaac Newton described gravity as a force that acts at a distance between two bodies. The Earth exerts a gravitational force on all objects, which causes them to fall towards the ground when they fall.

Combining concepts: acceleration due to gravity

Acceleration due to gravity, often represented by the letter g, is the acceleration experienced by an object when gravity is the only force acting on it. Near the surface of the Earth, g is about 9.81 meters per second squared (m/s²). This means that for every second that an object is in free fall, its velocity increases by about 9.81 m/s.

Mathematical representation

The formula for calculating the gravitational force acting on an object is given by Newton's second law of motion:

F = M * G

Where:

  • F is the gravitational force (also called weight), measured in newtons (N).
  • m is the mass of the object, measured in kilograms (kg).
  • g is the acceleration due to gravity, which is about 9.81 m/s² near the Earth's surface.

For example, if you have a rock with a mass of 2 kilograms, the force exerted by gravity on the rock can be calculated as:

F = 2 kg * 9.81 m/s² = 19.62 N

Experiencing gravity: visualizing the concept

Let's imagine a ball falling. As it falls, it will accelerate towards the ground due to gravity. We can represent this visually as below:

falling ball Quick

Free fall

When an object falls only under the influence of gravity, it is said to be in "free fall." During free fall, all objects accelerate toward Earth at the same rate, regardless of their mass. This concept was tested by Galileo Galilei and has been famously demonstrated through thought experiments such as dropping a feather and hammer on the moon, where there is no air resistance:

Suppose you stand on the moon and drop a hammer and a feather at the same time. Since there is no air resistance, both the hammer and the feather will fall to the surface of the moon simultaneously.

Factors affecting acceleration due to gravity

Although g is approximately 9.81 m/s² near the Earth's surface, various factors can slightly alter this value:

  • Altitude: The higher you are above the Earth's surface, the weaker the force of gravity, causing the acceleration due to gravity to decrease slightly.
  • Latitude: The Earth's rotation causes a slight variation in gravitational acceleration from the poles to the equator, affecting the measurement of g.
  • Local topography: Nearby mountains or dense areas can slightly alter the local gravity field, causing g to change.

Real-world applications and impact

Understanding and calculating the acceleration due to gravity has many practical applications in everyday life and scientific exploration:

  • Building construction: Engineers have to calculate gravitational forces to design stable structures that can withstand their weight and external forces such as wind.
  • Aviation: Pilots and engineers use the effects of gravity to plan flight paths and fuel requirements.
  • Space exploration: Astronauts experience microgravity in orbit, and understanding gravity helps launch spacecraft and land them safely.

Conclusion

Acceleration due to gravity is a fundamental concept that describes the rate of acceleration of objects toward Earth under the force of gravity. Its applications are very wide, affecting everything from the way we walk to the construction of buildings and the exploration of space. By understanding how gravity affects acceleration, one gains information about the motion of objects in our world and beyond.


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Acceleration due to gravity

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