Undergraduate
  1. Classical mechanics  1.1. dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. projectile motion  1.1.4. Relative speed  1.1.5. Uniform circular motion  1.1.6. Non-uniform circular motion  1.1.7. Reference frames and transformations  1.2. Newton's Laws of Motion  1.2.1. First law of motion  1.2.2. Second law of motion  1.2.3. Third Law of Motion  1.2.4. Applications of Newton's Laws  1.2.5. Friction and its types  1.2.6. Free Body Diagram  1.2.7. Constraints and pseudo-forces  1.3. Work and Energy  1.3.1. work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy in classical mechanics  1.3.5. Conservative and non-conservative forces  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.4. Speed and collisions  1.4.1. Linear momentum  1.4.2. Conservation of momentum  1.4.3. Impulse and impact force  1.4.4. Elastic and inelastic collision  1.4.5. Center of mass and speed  1.4.6. Rocket Propulsion  1.5. Rotational motion  1.5.1. Torque and Angular Momentum  1.5.2. Moment of inertia  1.5.3. Rotational Kinematics  1.5.4. Rotational Energy  1.5.5. Rolling Motion  1.5.6. Precession and gyroscopic motion  1.6. Gravitational force  1.6.1. Newton's law of universal gravitation  1.6.2. Gravitational potential energy  1.6.3. Orbital mechanics  1.6.4. Kepler's laws of planetary motion  1.6.5. Gravitational field and potential  1.7. Fluid mechanics  1.7.1. Pressure and Pascal's Principle  1.7.2. Buoyancy and Archimedes' principle  1.7.3. Fluid Dynamics and Bernoulli's Principle  1.7.4. Viscosity and Poiseuille's law  1.7.5. Surface tension and capillarity  1.8. Oscillations and waves  1.8.1. Simple Harmonic Motion  1.8.2. Damped and driven oscillations  1.8.3. Coupled oscillations and common modes  1.8.4. Wave properties and types  1.8.5. Sound Waves and the Doppler Effect  1.8.6. Wave interference and superposition
  2. Electromagnetism  2.1. Electrostatics  2.1.1. Electric charge and properties  2.1.2. Coulomb's law  2.1.3. Electric field and electric potential  2.1.4. Gauss's Law  2.1.5. Capacitance and Dielectric  2.1.6. Electric dipole and potential energy  2.2. Electric circuits  2.2.1. Current and Resistance  2.2.2. Ohm's law  2.2.3. Kirchhoff's Laws  2.2.4. RC Circuit  2.2.5. AC Circuits and Reactance  2.2.6. Electric power and energy  2.3. Magnetism  2.3.1. Magnetic Fields and Forces  2.3.2. Ampere's Law  2.3.3. Magnetic dipole moment  2.3.4. Biot-Savart law  2.3.5. Magnetic Materials and Hysteresis  2.4. Electromagnetic induction  2.4.1. Faraday's Law  2.4.2. Lenz's law  2.4.3. Self and mutual induction  2.4.4. Transformers and Inductive Circuits  2.5. Maxwell's equations  2.5.1. Gauss's law for electricity  2.5.2. Gauss's law for magnetism  2.5.3. Faraday's law of induction  2.5.4. Ampere-Maxwell law  2.5.5. Electromagnetic waves
  3. Thermodynamics  3.1. Laws of Thermodynamics  3.1.1. Zeroth law of thermodynamics  3.1.2. First law of thermodynamics  3.1.3. Second Law  3.1.4. Third Law  3.2. Heat and work  3.2.1. Heat transfer (conduction, convection, radiation)  3.2.2. Thermal expansion  3.2.3. Heat engines and refrigerators  3.2.4. Carnot cycle and efficiency  3.3. Statistical mechanics  3.3.1. Maxwell–Boltzmann distribution  3.3.2. Entropy and Probability  3.3.3. Partition function  3.3.4. Fermi–Dirac and Bose–Einstein statistics
  4. Optics  4.1. Geometrical Optics  4.1.1. Reflection and Refraction  4.1.2. Mirrors and lenses  4.1.3. Optical Instruments  4.1.4. Fermat's principle  4.2. Wave optics  4.2.1. Interference in wave optics  4.2.2. Diffraction  4.2.3. Polarization  4.2.4. Coherence and holography
  5. Quantum mechanics  5.1. Wave–particle duality  5.1.1. Blackbody radiation in wave–particle duality in quantum mechanics  5.1.2. Photoelectric effect  5.1.3. Compton scattering  5.1.4. De Broglie wavelength  5.2. Schrödinger Equation  5.2.1. Time-independent Schrödinger equation  5.2.2. Particle in a box  5.2.3. Quantum Tunneling  5.2.4. Potential wells and obstacles  5.3. Quantum States  5.3.1. Wave function  5.3.2. Quantum operators  5.3.3. Heisenberg uncertainty principle  5.3.4. Angular momentum and spin
  6. Relativity  6.1. Special relativity  6.1.1. Lorentz transformations  6.1.2. Time expansion and length contraction  6.1.3. Relativistic energy and momentum  6.2. General relativity  6.2.1. Principle of Equivalence  6.2.2. Schwarzschild metric  6.2.3. Gravitational waves  6.2.4. Black holes and event horizons
  7. Solid state physics  7.1. Crystal structure  7.1.1. Bravais lattices  7.1.2. X-ray diffraction  7.1.3. Band theory  7.1.4. Phonons and lattice vibrations  7.2. Electrical and Magnetic Properties  7.2.1. Conductors, Semiconductors and Insulators  7.2.2. Superconductivity  7.2.3. Hall effect
  8. Nuclear and particle physics  8.1. Atomic Structure  8.1.1. Atomic Model  8.1.2. Nuclear binding energy  8.2. Radioactivity  8.2.1. Alpha, beta, gamma decay  8.2.2. Half life  8.2.3. Nuclear Fission and Fusion  8.3. Particle physics  8.3.1. Standard Model  8.3.2. Quarks and Leptons  8.3.3. antimatter  8.3.4. Fundamental interactions
  9. Astrophysics and cosmology  9.1. Stellar evolution  9.1.1. Star formation  9.1.2. Black holes and neutron stars  9.1.3. White dwarfs and supernovae  9.2. Cosmology  9.2.1. The Big Bang Theory  9.2.2. Dark matter and dark energy  9.2.3. Cosmic microwave background

Undergraduate → Classical mechanics → Newton's Laws of Motion ↓


Friction and its types


Friction is one of the fundamental concepts in physics and plays a vital role in our daily lives and various scientific applications. It is the force that opposes the relative motion of two surfaces in contact or the tendency towards such motion. Understanding friction is essential in explaining why objects move or remain at rest, and it is deeply rooted in Newton's laws of motion. In this comprehensive exploration, we will take a deep look at the concept of friction, its types, and their implications in classical mechanics.

Nature of friction

Friction arises due to the interactions at the surfaces of two bodies in contact. At the microscopic level, the surfaces are not perfectly smooth, and irregularities or roughness at the contact points cause friction. This force acts parallel to the contact surface and in the opposite direction of the applied force or motion.

Example of friction in action

Consider the simple example of pushing a block on a table. To move the block, you need to apply a force that can overcome the friction between the block and the table. If the table were frictionless, even the smallest force would keep the block in constant motion.

Types of friction

Static friction

Static friction is the force that must be overcome to get an object moving at rest. It acts until the applied force exceeds its limit, causing the motion to stop. The maximum static friction is usually greater than the kinetic friction, which is why it is often easier to keep an object moving once it is in motion.

static friction

The mathematical representation of static friction can be expressed as:

f_s ≤ μ_s * N

Where f_s is the static friction force, μ_s is the static friction coefficient, and N is the normal force.

Dynamic friction

Kinetic friction comes into play when an object is already in motion. It is the force that opposes motion and usually has a smaller coefficient than static friction. This explains why it is easier to keep an object moving than to start it moving.

Kinetic friction

The expression for kinetic friction is given as:

f_k = μ_k * N

Where f_k is the kinetic friction force and μ_k is the coefficient of kinetic friction.

Rolling friction

Rolling friction (or rolling resistance) occurs when an object rolls on a surface. It is usually much smaller than static or kinetic friction, which is why wheels and ball bearings are effective at reducing friction.

Rolling friction

Rolling friction depends on factors such as the nature of the surfaces, the diameter of the wheels and the weight of the object.

Effect of friction in Newton's laws of motion

Newton's laws of motion describe how objects move and interact with forces. Friction plays an important role in these laws because it is often an unobserved force at work.

Newton's first law

Newton's first law states that an object will remain at rest or in uniform motion unless an external force is applied. Friction is the force that acts on an object at rest, and prevents it from moving unless a sufficient force is applied. When an object slides, kinetic friction eventually brings it to rest if no other force is involved.

Example of Newton's first law with friction

Imagine a hockey puck sliding across ice. There is very little friction on ice, allowing the puck to slide a long way before it stops. In contrast, a puck sliding across a rough surface such as carpet has to overcome a lot of friction, causing it to stop quickly.

Newton's second law

According to Newton's second law, the acceleration of an object is proportional to the total force acting on it and inversely proportional to its mass. Friction is often the opposing force in these scenarios, affecting the total force and thus the acceleration.

F_net = m * a

Where F_net is the net force, m is the mass, and a is the acceleration of the object.

Example of Newton's second law with friction

If you push a balloon on a table, acceleration occurs easily due to low friction. However, more force is required to push a book because the friction between the book and the table is more.

Newton's third law

Newton's third law states that for every action there is an equal and opposite reaction. When you walk, your foot pushes back on the ground, and the ground pushes you forward. The friction between your foot and the ground is the force that allows you to push yourself forward.

Example of Newton's third law with friction

Consider trying to walk on ice. The low friction doesn't allow your foot to push hard enough across the surface, increasing the chance of slipping or falling. Walking on a rough surface such as concrete shows how friction provides the resistance needed for walking.

Applications and examples of friction in real life

Friction is fundamental in engineering, transportation, and everyday activities. Here are some applications:

  • Braking system: Vehicles rely on the friction between the brake pads and the wheels to slow down or stop.
  • Grip: Friction helps athletes maintain their grip on sports equipment such as bats and rackets.
  • Tires: The tread of a tire increases friction with the road surface, improving traction and safety.
  • Machinery: In mechanical systems, unwanted friction is minimized through lubrication to prevent wear and overheating.
  • Everyday activities: Things like writing with a pen rely on the friction between the pen tip and the paper to transfer the ink.

Factors affecting friction

The magnitude of friction depends on several factors:

  • Surface roughness: Rough surfaces have greater friction due to greater surface irregularities.
  • Normal force: Friction increases as the normal force increases. Heavier objects usually have more friction.
  • Material properties: Different material combinations result in different coefficients of friction.
  • Temperature: Temperature can change the properties of a substance, which affects friction. For example, ice becomes more slippery when it melts a little.
  • Surface area: Contrary to intuition, contact area does not significantly affect friction. It is the nature of the surfaces in contact that matters more.

Friction coefficient

Coefficients of friction are numerical values that describe the ratio of the frictional force between two bodies to the force pressing them together. These are usually empirical values obtained from experiments.

Static and kinetic coefficients

As mentioned earlier, the static friction coefficient μ_s is usually greater than the kinetic friction coefficient μ_k. This difference explains the higher force required to move an object than to keep it in motion.

Example values

Some typical values of the coefficient of friction are:

  • Steel on steel: Static: 0.6, Dynamic: 0.5
  • Rubber on concrete: Static: 1.0, Kinetic: 0.8
  • Wood on wood: Static: 0.5, Kinetic: 0.3
  • Snow on snow: Static: 0.1, Kinetic: 0.03

Role of friction in energy and work

Friction affects not only motion but also the energy aspects of mechanical systems. Work and energy are important concepts in understanding the full effect of friction.

Work done by friction

When friction acts on a moving object, it does work on the object, converting kinetic energy into thermal energy. This is one reason why a constant force is needed to maintain motion in the presence of friction.

W = f_k * d

Where W is the work done by friction, f_k is the kinetic friction force, and d is the distance over which the force acts.

Energy dissipation

Energy lost due to friction is often converted into heat. This dissipation can be a gain or a loss depending on the situation. For example, brakes rely on friction to convert motion energy into heat to stop vehicles, while in engines, the excess heat may require additional cooling measures.

Conclusion

Friction is a multifaceted force that varies greatly depending on the specifics of the systems in contact. From simple actions like walking to complex industrial machines, friction significantly affects systems. It plays a key role in Newton's laws of motion and interacts with other physical forces in complex and sometimes surprising ways. A thorough understanding of friction provides insight into designing efficient systems, improving safety, and advancing technology in areas ranging from basic transportation to complex space explorations.


Undergraduate → 1.2.5


U
username
0%
completed in Undergraduate

← Prev (1.2.4)
Applications of Newton's Laws
Next (1.2.6) →
Free Body Diagram

Comments 



Friction and its types

https://www.physicsflow.com/ug/1.2.5?pfal=en