Answer:
Answer is c. 2
Explanation:
Since friction is present at the contact between 2 materials thus coefficient of friction always involve 2 materials
Explanation:
I am sorry. I don't understand too :/ I haven't learn engineering before- But if I'm not wrong, if something is black, probably it's burnt? Because you have to dip it in the water to cool down.
For example, if a steel is burnt, it will change color like blue.
So the answer is "burnt".