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 ↓


Types of Forces (Contact and Non-Contact)


Forces play an important role in the world of physics, especially when we explore the concept of motion. When you push a shopping cart, pull your chair closer, or watch a magnet attract a paperclip, you see forces in action. Forces are essentially interactions that change or tend to change an object's state of motion or rest. They can even change the shape of objects. In the world around us, forces are everywhere, affecting everything from a bird's flight to a planet's orbit.

Definition of force

Force is defined as the push or pull applied to an object. When you think of force, imagine actions like opening a door, closing a drawer, or lifting a bag. These all require the application of force. In scientific terms, force is an interaction that causes a change in the speed, direction, or shape of an object.

Types of forces

Forces can be broadly classified into two types: contact forces and non-contact forces. These classifications help us understand how different forces are applied and what effect they have on different objects.

Contact force

Contact forces occur when two interacting objects physically touch each other. These forces are clearly visible in everyday life and include several types:

1. Friction force

The friction force resists the sliding motion of two surfaces against each other. It is the force that makes it difficult to slide a book across a table. The direction of the friction force is always opposite to the direction of motion or the desired direction of motion.

Frictional Force = μ * Normal Force

Where μ represents the coefficient of friction, and normal force is the force perpendicular to the contact surface.

2. Tension force

Tension is the force transmitted through a wire, rope, cable or something similar when it is pulled tightly by forces acting from the opposite end. An example is the tension in a rope during a game of tug of war.

3. Normal force

Normal force is the supporting force applied to an object that is in contact with another stationary object. For example, if a book is placed on a table, the table exerts an upward normal force on the book.

4. Air resistance force

Air resistance, also known as drag, is a type of frictional force that acts against a moving object as it travels through the air. This force is seen when a parachute slows down a skydiver's descent.

5. Applied force

Applied force is the force exerted on an object by a person or another object. If you push a trolley in a store, the force exerted by your hands is the applied force.

6. Spring force

The spring force is applied by a compressed or stretched spring to any object attached to it. It depends on Hooke's law:

F = -kx

Where F is the force applied by the spring, k is the spring constant, and x is the distance the spring is stretched or compressed from its original length.

Spring

The blue lines represent the spring, which serves to restore its original form.

Non-contact forces

As the name suggests, non-contact forces act on objects without any physical connection. Forces of this nature can affect objects even from a distance. Some major examples are:

1. Gravitational force

Perhaps the most universally recognized force, gravity is the force of attraction between two objects with mass. This is why objects fall to the ground when they are dropped. Gravity can be calculated using Newton's law of universal gravitation:

F = G*(m1*m2)/r^2

Where F is the force between the masses, G is the gravitational constant, m1 and m2 are the two masses, and r is the distance between the centers of the two masses.

Earth Moon

The green line symbolizes the gravitational force between the Earth and the Moon.

2. Electromagnetic force

This force acts between charged particles. It is responsible for the interactions between atoms and the forces that hold substances together. Electric forces can either attract or repel, depending on the nature of the charges involved (e.g. like charges repel while opposite charges attract).

3. Magnetic force

Magnetic force is applied to magnets and magnetic materials by currents. It is produced by the movement of electric charges. When you bring a magnet near a refrigerator and it sticks, you see the magnetic force in action.

4. Nuclear force

The nuclear force is the force that holds the nuclei of atoms together. This force is extremely important at the atomic level and is responsible for the binding of protons and neutrons within the atomic nucleus.

Visualization of forces

Think of forces as arrows. Arrows help clarify the direction and magnitude of forces. The direction of the force is shown by the direction of the arrow, while the length of the arrow indicates the magnitude. For example, a longer arrow indicates a greater force.

F1 F2

In the above example, F1 is greater than F2, as indicated by the length of the arrows.

Force and speed

The relationship between force and motion is described through Newton's laws of motion:

Newton's first law

An object remains at rest or in uniform motion in a straight line unless affected by an external force. This is often called the law of inertia.

Newton's second law

The second law describes how the velocity of an object changes when an external force is applied to it. It can be expressed by the formula:

F = ma

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

Newton's third law

For every action there is an equal and opposite reaction. This means that forces always occur in pairs.

Action Feedback

In a situation like a swimmer pushing against water, the swimmer moves forward while the water pushes backward with equal force.

Conclusion

In short, forces are integral to understanding motion and the physical interactions that shape our universe. By classifying them into contact and non-contact forces, we can better analyze their effect on different systems. Whether through the gravitational pull that binds us to the Earth or the tension in a rope during climbing, forces govern our daily experiences and play a vital role in the mechanics of motion.


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Application of Newton's laws in daily life
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Types of Forces (Contact and Non-Contact)

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