They use a formula and that formula is 
People/Land Area=Population Density
        
                    
             
        
        
        
Explanation:
1.Law of Inertia
<em>Inertia</em><em> </em>: is the ability to resist change in motion.
<em>Example</em><em>;</em><em> </em><em>if you roll a ball it will keep running unless you</em><em> change </em><em>it's</em><em> </em><em>direction with the help of </em><em>friction.</em><em>.</em>
2. second law of motion states that an object will accelerate when an unbalanced force is applied on a mass..
<em>unbalanced force is a type of force</em><em> where total force</em><em>≠</em><em>zero</em><em>,</em><em> </em><em>means the object will move</em><em>.</em><em>.</em>
<em>Example</em><em>;</em><em> if you will try to push a truck</em><em> will be less but if you push a car the acceleration will be more</em><em>.</em><em>.</em><em> because </em><em>c</em><em>ar has less </em><em>mass.</em><em>.</em>
<em>3</em><em>.</em><em> the third law of motion state that foreign every</em><em> action there is a opposite reaction</em><em>.</em><em>.</em>
<em>Example</em><em>;</em><em> can you throw a ball on the floor </em><em>.</em><em>.</em><em>.</em><em>the floor </em><em>pushes</em><em> </em><em>back</em><em> that the ball</em><em>.</em><em>.</em>
hope it helps
 
        
             
        
        
        
Answer:
Biotic: Plants
Abotic: Rocks
Explanation:
A biotic factor is something in an ecosystem or environment that is living. Some examples that could be found in a park are grass, flowers, trees, squirrels, pigeons, fish or people. 
An abiotic factor is the exact opposite of a biotic factor: something in an ecosystem or environment that is not alive. Some examples that may be found in a city park include a park bench, a trash can, rocks, a playground, a pool, basketball court, temperature, and humidity. 
 
        
             
        
        
        
Your answer is D
Gravel sized particals
Enjoy your answer