What would be an ideal experiment to test how different types of surfaces affect friction?
A) Two objects of equal weight placed on two glass surfaces of equal lengths.
B) Two objects of equal weight placed on two glass surfaces of unequal lengths.
C) Two objects of equal weights placed on a glass surface and a wooden surface.
D) Two objects of different weights placed on two wooden surfaces of unequal lengths.

Question

What would be an ideal experiment to test how different types of surfaces affect friction?
A)	Two objects of equal weight placed on two glass surfaces of equal lengths.	
B)	Two objects of equal weight placed on two glass surfaces of unequal lengths.	
C)	Two objects of equal weights placed on a glass surface and a wooden surface.	
D)	Two objects of different weights placed on two wooden surfaces of unequal lengths.

burrella · Answer

The answer is C. Let's talk about why that is. The question is asking about SURFACE TYPE that's the "manipulated variable" the thing you change to test. A doesn't test anything because there are to identical conditions. B The manipulated variable here is length, not surface type. D the manipulated variable in D is also length. C is the correct answer because the manipulated variable is surface type (wood vs glass).