The substances which reduce friction are called _______.

The correct answer is Lubricants.

Key Points

• Lubricants:-
  • These are substances that are introduced between two surfaces in contact in order to reduce friction. (Hence option 4 is correct)
  • They do this by forming a thin layer between the surfaces, which prevents them from rubbing directly against each other.
  • This reduces the amount of heat generated and the wear and tear on the surfaces. 
  • There are many different types of lubricants, including:
    • Oils
    • Greases
    • Solids, such as graphite and molybdenum disulfide
    • Liquids, such as water and silicone
    • Gases, such as air and nitrogen

Additional Information

• Fluids:-
  • These are substances that can flow easily and continuously deform under an applied shear stress, or external force.
  • They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear force applied to them.
• Magnet:-
  • It is a material or object that produces a magnetic field.
  • This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets.
• Spring:-
  • It is an elastic object that stores mechanical energy and releases it when the opposing force is removed.
  • Springs can be made from a variety of materials, including metal, plastic, and rubber.
  • They come in all shapes and sizes, and can be used in a wide variety of applications.