Explain some methods of reducing friction between of matyer

Step-by-step explanation:

1. Use of lubricants

Lubricants like oil and grease helps to decrease friction by forming a thin film in between different parts of the machine. This film covers up the scratches and bumps on the surfaces of different parts. This reduces interlocking between the two surfaces.  Thus reducing the friction.

2. Use ball bearings

Two moving surfaces in a machine are attached by placing small steel balls or steel rollers  in between them. This way, the moving parts avoid direct contact and the force of sliding friction turns into rolling friction. Rolling friction is less than sliding friction, in doing so reducing the friction.

3. Polishing

Polishing reduces the unevenness  of a surface. This will reduce interlocking between the surfaces.  

4. Streamlining

Streamlining is the process where you make a machine in a shape that avoids air and water resistance. This reduces friction because a streamlined object cuts through the water and air molecules.

∠1≅∠2 by the alternate exterior angles theorem.

step-by-step explanation:

given, a ∥ b and ∠1 ≅ ∠3 .we have to prove that e ∥ f

we know that ∠1≅∠3 and that a || b because they are given. we see that by the alternate exterior angles theorem. therefore, ∠2≅∠3 by the transitive property. so, we can conclude that e || f by the converse alternate exterior angles theorem.

we have to fill the missing statement.

transitivity property states that if a = b and b = c, then a = c.

now, given ∠1≅∠3 and by transitivity property ∠2≅∠3 .

hence, to apply transitivity property one angle must be common which is not in result after applying this property which is ∠1.

the only options in which ∠1 is present are ∠1 and ∠2, ∠1 and ∠4

∠1 and ∠4 is not possible ∵ after applying transitivity we didn't get ∠4.

hence, the missing statement is ∠1≅∠2.

so, ∠1≅∠2 by the alternate exterior angles theorem.