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 ↓


Friction and its effects


Friction is an everyday force that opposes motion between two surfaces that are in contact with each other. It plays an important role in our daily lives as well as in physics, affecting how objects move and interact. Understanding friction is essential in mechanics, especially when discussing force and the laws of motion.

What is friction?

Friction is a force that opposes the relative motion of two surfaces in contact or the tendency to such motion. Its direction is always opposite to the direction of motion or the intended direction of motion. Friction occurs because surfaces have microscopic imperfections, which interact with each other.

Visual example of friction

block Applied force

In the figure given above, a block lies on a horizontal surface. When the applied force (shown in red) tries to slide the block to the right, friction acts in the opposite direction.

Types of friction

Friction may be divided into several types depending upon the conditions of motion of the object on the surfaces:

  • Static friction: It is the frictional force that acts on a stationary object. Static friction must be overcome to make the object move.
  • Kinetic friction: It is also called sliding friction. This force acts on a moving object. It is usually less than static friction.
  • Rolling friction: This friction occurs when an object rolls on a surface, such as a wheel on a road.

Effects of friction

Friction has several important effects on the motion of objects:

  1. Prevents motion: Friction prevents unwanted motion, such as when walking over a rough surface without slipping.
  2. Heat is generated: Friction can generate heat, which you can feel if you rub your hands together.
  3. Wear on surfaces: Over time, friction can wear down materials, such as shoe soles.

Mathematical representation of friction

The friction force can be calculated using the following formula:

F_friction = μ * N

Where:

  • F_friction is the friction force.
  • μ is the coefficient of friction (dimensionless).
  • N is the normal force (the perpendicular force between the surfaces).

Example problem

Consider a box weighing 50 N that rests on a surface. If the coefficient of static friction between the box and the surface is 0.4, determine whether a horizontal force of 15 N applied to the box will move it.

The maximum static friction can be calculated as:

F_friction_max = μ * N = 0.4 * 50 N = 20 N

Since the applied force (15 N) is less than the maximum static friction (20 N), the box does not move.

Friction in different situations

Walking

When you walk, the friction between your shoes and the ground provides necessary grip. Without enough friction, you can slip and fall.

Vehicles

Vehicle tires depend on friction to move effectively on roads. Tires are designed to maximize friction, especially in wet conditions to prevent slipping.

Visual example of movement with friction

Feet Friction force

This visual example shows how friction provides resistance when a foot attempts to move forward while walking, preventing slipping.

Reducing friction

Sometimes, it is necessary to reduce friction to improve the efficiency of motion or to reduce wear and tear. Here are some ways to reduce friction:

  • Lubrication: Applying oil or grease to surfaces can reduce friction by forming a film that separates the surfaces.
  • Using smooth surfaces: Polishing surfaces can reduce the friction between them.
  • Use of rollers or bearings: This can convert sliding friction into rolling friction, which is smaller.

Visual example of lubrication

Surface Lubrication Reducing friction

In the visual example, adding a lubricant (green layer) between the surfaces reduces the friction force.

Conclusion

Friction, though often troublesome, is an essential element of physics and everyday life. Its ability to resist and affect motion affects everything from simple walking to complex machinery. Understanding its properties and how to control friction can lead to improved efficiency in a wide range of applications.


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Friction and its effects

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