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


In the study of physics, it is fundamental to understand the concept of force and the laws of motion. These principles have been essential to understanding the behavior of objects in the world around us. This exploration will introduce you to the basics and lead to more complex ideas about motion and the forces that affect it.

What is force?

Force is essentially a push or pull that acts on an object. It can make an object start moving, stop moving, change direction, or change its shape. In everyday life, we encounter force in many forms, such as the frictional force that prevents us from slipping when walking, the gravitational force that keeps us grounded, or the tension force that allows us to pull a rope.

Measurement of force

The standard unit of force in the International System of Units (SI) is the newton, represented by "N." One newton is the amount of force needed to accelerate a one-kilogram mass by one meter per square second. Mathematically, this can be represented as:

1 N = 1 kg·m/s²

Types of forces

Various forces act on objects. Some common types of forces are as follows:

  • Gravitational force: An attractive force that pulls objects toward one another. Earth's gravity pulls everything toward its center.
  • Normal force: The supporting force applied to an object when it comes into contact with another stationary object. For example, a book placed on a table experiences a normal force applied upward by the table.
  • Friction force: The force exerted by an object on a surface when it moves on it or attempts to move on it. The friction force acts in the opposite direction to the moving object.
  • Tension force: The force applied to a wire, rope, or cable when it is pulled by forces acting from opposite ends.
  • Air resistance force: A type of frictional force that acts against objects as they travel through the air.
  • Applied force: The force that is applied by someone or another object.

Illustration of forces with examples

To see the forces at work, consider a person pushing a box. This action involves the force applied by the person pushing. If the box moves on the floor, the friction between the box and the floor opposes the force applied.

Newton's laws of motion

Sir Isaac Newton formulated three laws of motion that describe the behavior of objects under the influence of forces. These laws laid the foundation of classical mechanics.

Newton's first law of motion (law of inertia)

This law states: "An object at rest will remain at rest, and an object in motion will continue to move with a constant velocity, unless an external force is applied." It is often called the law of inertia.

Example: Imagine a book sitting on a table. The book will remain at rest unless someone applies an external force to move it. Similarly, a rolling ball will continue to roll in a straight path unless friction or some other external force slows it down.

Newton's second law of motion

This law describes how the velocity of an object changes when an external force is applied to it. It is briefly expressed by this formula:

F = m·a

Where F is the applied force, m is the mass of the object, and a is the acceleration produced.

Example: If you kick a football, it accelerates because of the force you apply to it with your foot. Heavier objects require more force to achieve the same acceleration, as shown in the formula. For example, kicking a bowling ball requires a lot more force to achieve the same speed as a football.

Newton's third law of motion

This law is often summarized as: "For every action, there is an equal and opposite reaction." This means that forces always come in pairs. When one object exerts a force on another object, the second object exerts an equal force in the opposite direction on the first object.

Example: When you jump out of a boat, you push the boat backward (action), and the boat pushes you forward (reaction). Similarly, when birds fly, their wings push air downward, and the air pushes them upward.

Examples of the implementation of Newton's laws

Let's look at some everyday examples of Newton's laws:

Example #1: Bicyclist

When a cyclist pedals a bicycle, the wheels rotate and push against the ground. According to Newton's third law, the ground pushes back on the wheels with an equal force. This reaction propels the bicycle forward. Additionally, when the cyclist stops pedaling, the friction force acts in the opposite direction, slowing down the bicycle, which is derived from Newton's first law of inertia.

Example #2: Car accident

In the event of a car accident, the impact force stops the vehicle almost instantly. However, passengers inside continue to move forward due to inertia (Newton's first law), which is why seat belts are important - they apply an outward force to keep passengers in place.

Balanced and unbalanced forces

Understanding balanced and unbalanced forces is important for analyzing motion:

Balanced forces

When forces are balanced, they cancel each other out, and there is no change in motion. If an object is at rest or moving at a constant velocity, the forces acting on it are balanced.

Unbalanced force

When forces are unbalanced, they do not cancel out perfectly, and the motion of an object changes. This change may include speeding up, slowing down, or changing direction. Newton's second law describes this situation, because unbalanced forces result in acceleration.

Free body diagram

Free body diagrams are used in physics to show the forces acting on an object. They help to visualize the strength and direction of the forces. Here is a simple example of a box sliding on a frictionless surface:

clashpushweightGeneral

In this diagram, the forces acting on the box include friction acting opposite the direction of the applied push, the weight of the box acting downward, and the normal force acting upward, which is equal and opposite to the weight of the balanced forces.

Conclusion

The study of force and motion equips us with a deeper understanding of the physical universe. From simple activities like walking to advanced technologies like rocket launches, Newton's laws provide the foundational knowledge for understanding these phenomena. With this understanding, we can analyze and predict the motion of objects, bringing the physical world closer to our understanding.


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Laws of force and motion

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