Usually liquids (like oil).
Oil is used to reduce friction.
Oil is mainly used to reduce friction between contacting surface, e.g., metal on metal - not to reduce air friction.
Lubricants.
yes.
heat
To reduce the coefficient of friction.
To reduce unwanted friction.
Yes, Oil forms a coating on the cylinder walls to reduce friction and is also used as a coolant to protect engine parts
OIL == ==
There are two most widely used methods to reduce friction__Using lubricants.Converting Sliding Friction into Rolling Friction
Motor oil is used as a lubricant to reduce sliding friction and create a layer of fluid friction, known as hydrodynamic or fluid film lubrication, between moving parts. This helps to reduce wear and heat generated by friction in the engine.
oil or grease