Answer:
d. changing refractive index of gases in the atmosphere
Explanation:
light from a star passes through the atmosphere to reach our eyes. however, the layers of gases in the atmosphere are in constant motion, so the light gets bent and appears to be flickering.
i hope this helps! :D
 
        
             
        
        
        
The force of friction that is acting on the suitcase is the force that opposes the motion of the suitcase.
<h3>What is friction?</h3>
The force that resists the motion between two bodies in contact. There are some materials that reduces friction such as oil in a car engine reduces friction. In this example, friction creates between the motion of suitcase and with the ground.
So we can conclude that the force of friction that is acting on the suitcase is the force that opposes the motion of the suitcase.
Learn more about force here: brainly.com/question/12970081
#SPJ1
 
        
             
        
        
        
Refraction of light is the process we take advantage of when we use eyeglasses.
        
             
        
        
        
Answer:
The three laws of motion were first compiled by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687.
Explanation:
 
        
             
        
        
        
Answer:
30 N
Explanation:
there are two forces act on the bar:
- weight of 1.5 kg mass, w = mg = 15 N
- weight of the bar, wb 
for balance,
w * Lw = wb * Lwb
Lw = length of bar from the mass to the pivot
Lwb = lenght of bar from the center of the bar to the pivot
15 * 20 = wb * (50-20) 
300 = wb * 30
wb = 300/30 = 30 N