<span>A lubricant such as oil, grease, graphite powder can reduce the friction between two surfaces. Or using metal balls to space them and reduce the contact surface area as used in ball bearings.</span>
Answer:3.51
Explanation:
Given
Coefficient of Friction 
Consider a small element at an angle \theta having an angle of 
Normal Force

Friction 

and 







<span>The unknown substance is silver.
I don't see a list of available substances, but let's see if there's something reasonable available that will match. First, let's calculate the density of the unknown substance. Density is mass per volume, so
273 g / 26 mL = 10.5 g/mL
Looking up a list of elements sorted by density, I see the following:
10.07 Actinium
10.22 Molybdenum
10.5 Silver
11.35 Lead
And silver at 10.5 g/ml is a very nice match for the unknown substances' density of 10.5 g/ml.</span>
Answer:
B
Explanation:
if you sit up straight you will have a proper posture
Number 13 is D the heart has 4 chambers and pumps blood to the arteries and number 14 us C