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 → Laws of force and motion ↓


newton's first law of motion


Newton's first law of motion is one of the fundamental concepts of physics. It describes how an object behaves when it is not under the influence of any force or when the sum of the forces is zero. Understanding this law helps us understand the nature of motion and the way objects interact with their environment.

Law stated in simple language

Newton's first law of motion, also called the law of inertia, states:

"Unless an object is at rest, it will remain at rest, and unless an object is in motion, it will continue to move with a constant velocity, unless an external force is applied on it."

In simple words, an object will not change its state of motion (be it at rest or in motion) unless a force compels it to do so.

Understanding inertia

Inertia is the property of an object that resists changes in its state of motion. The greater the mass of an object, the greater its inertia. This is why a heavy rock is more difficult to push than a small rock; the rock has more mass and therefore more inertia.

The concept of inertia means that an object will not start moving on its own, nor will a moving object stop or change direction without some kind of force.

Example: A ball on the ground

Consider a ball lying on the ground. If you do nothing to it, the ball will remain at rest. This is because there is no net force acting on it. Now, if you kick the ball, you apply a force that causes it to move. Once in motion, the ball will continue to move at a constant speed in a straight line due to inertia. It will stop only when a force, such as friction with the ground or an obstacle, acts on it.

ball at rest

Dynamic objects

According to Newton's first law, if an object is already in motion and no external force is applied to it, it will continue to move at the same speed and in the same direction. This may seem contradictory because we often see objects slowing down and stopping due to friction and other forces.

Example: Skater in motion

Imagine a skater sliding on smooth ice. If the skater doesn't push forward, they will maintain their speed and direction as long as there is little friction between the ice and the skates. The smoother the surface, the closer the skater's motion will be to a perfect example of Newton's first law.

Skater in motion

Forces and their effects

In real-world scenarios, forces often act on objects, causing a change in motion. Some common forces include gravity, friction, air resistance, and applied forces such as push or pull.

Example: A book on the table

If a book is placed on a table, it stays in place because the forces acting on it are balanced. The force of gravity pulls it down, while the supporting force from the table pushes it up. These forces cancel each other out, and the total force is zero.

Support Force Gravity

Mathematical formulation

Newton's first law can also be expressed mathematically. Consider the total force acting on an object:

    Force (F) = Mass (m) × Acceleration (a)

If there is no net force acting on the object:

    f = 0

Therefore, without applying any force, the object maintains its position:

    a = 0

This means that the velocity is constant, and therefore, the object either remains at rest or continues moving at a constant velocity if already in motion.

Practical applications in daily life

Understanding Newton's first law is important not only in physics but also in everyday life and engineering. This explains why seatbelts are important in vehicles. When a car stops suddenly, the person inside keeps moving forward due to inertia. The seatbelt provides the force needed to stop the person from moving forward, keeping him safe.

Example: Traveling on a bus

Standing on a bus, you may notice that when the bus speeds up, you lean backward. This is due to your inertia; your body wants to remain stationary while the bus moves forward. Conversely, when the bus speeds down, you may lean forward because your body wants to continue moving at the previous speed.

Bus

Conclusion

Newton's first law of motion provides profound insight into how objects behave when subjected to a force or in the absence of one. By understanding the principles of inertia and the effect of balanced and unbalanced forces on an object, we can explain and predict the motion of objects in a variety of situations. An appreciation of these fundamental concepts lays the groundwork for more advanced study in physics and other scientific fields.


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