If the billiard ball is going at the constant speed and contains its mass then the momentum WONT be changing. But realistically you have external forces like friction and air resistance changing the velocity thus changing the momentum. In this case momentum is not conserved because you're introduction an external force.
Answer:
Friction occurs because no surface is perfectly smooth.
Explanation:
Friction occurs because no surface is perfectly smooth. Rougher surfaces have more friction between them. Heavier objects also have more friction because they press together with greater force. Friction produces heat because it causes the molecules on rubbing surfaces to move faster and have more energy.
Answer:
force is a push or a pull
Answer:
a) 
b) 
Explanation:
From the question we are told that:
Separation distance 
Acceleration 1 
Acceleration 2 
Mass 1 
Generally the equation for Force is mathematically given by

For Particle 1


Also

Where

Therefore


b)
Generally the equation for Force is mathematically given by


