Grade 11
  1. Mechanics  1.1. dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two and three dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration and deceleration  1.1.6. Graphical analysis of motion  1.1.7. Equations of motion (advanced derivations)  1.1.8. Free fall and terminal velocity  1.1.9. Projectile motion  1.1.10. Relative velocity in one and two dimensions  1.1.11. Motion of a car on an inclined plane  1.2. Dynamics  1.2.1. Newton's laws of motion and their applications  1.2.2. Inertia and Newton's first law  1.2.3. Force and types of force  1.2.4. Static and kinetic friction  1.2.5. Circular motion and centripetal acceleration  1.2.6. Non-uniform circular motion  1.2.7. Banking of roads and curves  1.2.8. Momentum and Impulse  1.2.9. Conservation of momentum in one and two dimensions  1.2.10. Applications of Newton's Third Law  1.3. Work, Energy and Power  1.3.1. Work done by a constant and variable force  1.3.2. Work–energy theorem  1.3.3. Kinetic and potential energy  1.3.4. Gravitational and elastic potential energy  1.3.5. Conservation of mechanical energy  1.3.6. Power and instantaneous power  1.3.7. Efficiency of machines  1.3.8. Work done by conservative and non-conservative forces  1.4. Rotational motion  1.4.1. Torque and angular acceleration  1.4.2. Rotational equilibrium  1.4.3. Moment of inertia and its applications  1.4.4. Angular momentum and its conservation  1.4.5. Kinetic energy of rolling motion and rotation  1.4.6. Parallel and Perpendicular Axis Theorem  1.4.7. Dynamics of rotational motion
  2. Gravitational force  2.1. Universal gravitation  2.1.1. Newton's law of universal gravitation  2.1.2. Gravitational field and potential  2.1.3. Change in acceleration due to gravity  2.1.4. Kepler's laws of planetary motion  2.1.5. Orbital mechanics and satellites  2.1.6. Escape velocity and orbital velocity  2.1.7. Weightlessness and free fall  2.1.8. Gravitational potential energy and energy in orbits  2.1.9. Black holes and gravitational lensing
  3. Properties of matter  3.1. Fluid mechanics  3.1.1. Density and pressure in liquids  3.1.2. Pascal's theory and applications  3.1.3. Archimedes' Principle and Buoyancy  3.1.4. Bernoulli's equation and applications  3.1.5. Continuity equation and the Venturi effect  3.1.6. Surface tension and capillarity  3.1.7. Viscosity and Poiseuille's Law  3.1.8. Reynolds number and turbulence  3.2. Elasticity and deformation  3.2.1. Hooke's law and the stress-strain relation  3.2.2. Elastic modulus and applications  3.2.3. Deformation and yield strength of solids
  4. Thermal physics  4.1. Heat and temperature  4.1.1. Thermometric properties and temperature scale  4.1.2. Thermal expansion of solids, liquids and gases  4.1.3. Heat transfer system  4.1.4. Specific heat capacity and calorimetry  4.1.5. Latent heat and phase change  4.2. Kinetic theory of gases  4.2.1. Molecular model of gases  4.2.2. Kinetic explanation of temperature  4.2.3. Ideal Gas Equation and Deviations  4.2.4. Mean free path and Maxwell–Boltzmann distribution  4.3. Laws of Thermodynamics  4.3.1. Zeroth Law and Thermal Equilibrium  4.3.2. First Law and Internal Energy  4.3.3. The Second Law and Entropy  4.3.4. Carnot cycle and heat engines  4.3.5. Refrigerators and heat pumps
  5. Waves and oscillations  5.1. Simple Harmonic Motion  5.1.1. Equations of SHM  5.1.2. Energy in SHM  5.1.3. Damped and forced oscillations  5.1.4. Resonance and applications  5.1.5. Pendulum and spring-mass system  5.2. Wave motion  5.2.1. Types of mechanical waves  5.2.2. Wave motion and energy transport  5.2.3. Superposition Principle and Standing Waves  5.2.4. Reflection, Refraction and Diffraction  5.2.5. Doppler effect in sound and light  5.2.6. Pulsations and interference
  6. Electricity and Magnetism  6.1. Electrostatics  6.1.1. Electric charge and conservation  6.1.2. Coulomb's law and its applications  6.1.3. Electric field and electric flux  6.1.4. Electric potential and potential energy  6.1.5. Capacitance and Energy Stored in a Capacitor  6.2. Current Electricity  6.2.1. Ohm's law and electrical resistance  6.2.2. Resistivity and temperature dependence  6.2.3. Kirchhoff's Laws and Circuit Analysis  6.2.4. Electrical power and efficiency  6.2.5. Combination of resistors  6.3. Magnetism and Electromagnetism  6.3.1. Magnetic fields and their sources  6.3.2. Magnetic force on moving charges  6.3.3. Electromagnetic induction  6.3.4. Faraday's and Lenz's laws  6.3.5. Inductance and Transformer  6.3.6. Alternating current and its applications
  7. Optics  7.1. Reflection and Refraction  7.1.1. laws of reflection and refraction  7.1.2. Mirrors and lenses  7.1.3. Total internal reflection and optical fiber  7.2. Wave optics  7.2.1. Interference and Diffraction  7.2.2. Young's double-slit experiment  7.2.3. Polarization of light
  8. Modern Physics  8.1.1. Photoelectric effect and Einstein's theory  8.1.2. Wave–particle duality  8.1.3. Heisenberg's uncertainty principle  8.1.4. Compton Effect  8.2. Atomic and Nuclear Physics  8.2.1. Atomic model and energy levels  8.2.2. Radioactive decay and half-life  8.2.3. Nuclear Fission and Fusion
  9. Electronics and Communication  9.1. Semiconductors  9.1.1. pn junction and diode  9.1.2. Transistors and Logic Gates  9.1.3. Integrated Circuits and Applications  9.2. Communication Systems  9.2.1. Basics of Analog and Digital Communication  9.2.2. Wireless and Optical Communication  9.2.3. Modulation and Demodulation

Grade 11 → Mechanics → Dynamics ↓


Static and kinetic friction


Friction is an important concept in physics that opposes the motion of objects. When discussing friction in dynamics and mechanics, we mainly talk about two types: static friction and kinetic friction. These forces play an important role in everyday life and various mechanical systems.

What is friction?

Friction is the resistance that one surface or object experiences when moving over another. It acts in the opposite direction of motion, making it a force that opposes motion. Friction is the reason why cars stop when we apply brakes, we are able to walk without slipping, and objects eventually come to a stop.

How is friction produced?

Friction arises due to the microscopic roughness of surfaces. Even surfaces that appear smooth are rough at the microscopic level. When two surfaces come into contact, their irregularities rub against each other, causing resistance to motion.

Visual representation of friction

Surface 1 Surface 2 block Force

Static friction

Static friction is the friction that exists between a stationary object and the surface it rests on. This type of friction must be overcome for an object to start moving. It adjusts its magnitude to match the applied force up to a certain limit, known as maximum static friction.

Characteristics of static friction

  • Static friction prevents the initiation of motion.
  • It is equal and opposite to the force applied, up to the point where the motion starts.
  • The maximum static friction is given by the following expression: 
    f_s ≤ μ_s N
    where f_s is the static friction, μ_s is the coefficient of static friction, and N is the normal force.

Example of static friction

Consider a box placed on a flat surface. If you push the box gently, it does not move. Static friction is balancing the applied force. As you apply more force, the static friction increases up to a certain limit. Once the maximum static friction is crossed, the box starts moving.

Kinetic friction

Kinetic friction, also called sliding friction, occurs when an object is moving. It is usually less than the maximum static friction and remains relatively constant for different speeds of motion.

Characteristics of kinetic friction

  • Kinetic friction acts on moving objects.
  • It is usually weaker than static friction.
  • The kinetic friction is given by the formula: 
    f_k = μ_k N
    where f_k is the kinetic friction, μ_k is the coefficient of kinetic friction, and N is the normal force.

Example of kinetic friction

If the box you pushed earlier starts to slide, the friction acting on it is now kinetic friction. Unless there is a significant change in the weight of the box or the surface, it will remain constant as the box continues to move.

Comparison between static and kinetic friction

static friction Kinetic friction

In the above illustration:

  • The blue curve indicates increasing static friction up to the maximum point.
  • The red line represents the static kinetic friction after the initial speed.

Implications of friction in real life

Friction has a tremendous impact on everyday life and technology. Here are some of the applications and implications of friction:

Applications of friction

  • Walking: Walking would be impossible without friction between our shoes and the ground.
  • Driving: Cars move and stop effectively due to the friction between the car's tires and the road surface.
  • Climbing: Friction enables climbers to grip surfaces and climb up them.

Challenges posed by friction

  • Wear and tear: Constant friction causes wear and tear on mechanical parts, requiring maintenance and repairs.
  • Energy losses: Friction converts kinetic energy into heat, causing energy inefficiency in engines and machines.

Factors affecting friction

Various factors determine the magnitude of friction between two surfaces:

Surface texture

  • Rough surfaces have greater friction, since they have more irregularities that cling to one another.
  • Smooth surfaces have less friction because there is less contact at the microscopic level.

Normal force

The force with which the surfaces are pressed against each other affects the friction. An increase in the normal force generally results in an increase in friction.

Type of material

Different materials have different inherent resistance to sliding against each other, described by the coefficient of friction.

How to reduce friction

Sometimes, it is desirable to reduce friction. Here are ways to achieve this:

Lubrication

Applying a substance such as oil or grease between the surfaces reduces the direct contact, thus reducing friction.

Smoothing the surfaces

Polishing or coating the surfaces can reduce irregularities, thereby reducing friction.

Using rollers or ball bearings

The friction is reduced considerably by replacing sliding motion with rolling motion. For this reason, roller bearings are extensively used in machinery.

Conclusion

Understanding static and kinetic friction is vital to mastering dynamics in physics. It helps us understand how objects interact with surfaces and what are the forces involved in preventing or enabling motion. Mastering these concepts helps one control and optimize friction in practical scenarios, from designing efficient machines to ensuring safety in transportation. Through exploring the intricacies of friction, one gains a deeper understanding of the forces that govern motion in the physical world, leading to advances in technology and improvements in daily life.


Grade 11 → 1.2.4


U
username
0%
completed in Grade 11

← Prev (1.2.3)
Force and types of force
Next (1.2.5) →
Circular motion and centripetal acceleration

Comments 



Static and kinetic friction

https://www.physicsflow.com/g11/1.2.4?pfal=en