The first of Newton's three laws is that when the change in momentum is zero, momentum is conserved. This first law is often stated as an object at rest, tends to remain at rest, an object in motion tends to remain in motion, unless acted on by an outside force. An object at rest, such as a marble, sitting here on the floor with a velocity of zero, will tend to remain at rest, unless acted upon by an external force. The marble will not start moving, unless some outside force, some external force is applied to the marble. Momentum is conserved, the momentum is zero, and the momentum remains zero. For a moving object, the object will tend to remain in motion. The momentum will be conserved, unless there are external forces acting. A ship such as this kioa ship coming into stock has a significant momentum. Even though the velocity is very low, the mass is quite large. Getting this ship to stop will require a large external force. If no force is applied, that force usually being applied by the propellers. If no force is applied, the ship will keep on traveling in the same direction, but potentially in the water for many miles. It will just simply coast in the water very slowly, but it will continue to move forward. Objects in motion do tend to remain in motion. This is a little confusing, because our experiences that objects in motion tend to come to a stop. But that's because of an external force called friction. We experience a lot of friction in our daily lives. In fact, the whole reason we can walk is because of friction between our feet and the floor. If you've ever been on a wet floor or wet tile floor in zorries, you'll realize how important friction is. You tend to slip and fall because you've lost friction, an external force. So, things in motion do tend to remain in motion. And that is the second part of Newton's first law. Unless acted on, as I said, by an external or outside force, they're amusing external and outside interchangeably. This is Newton's first law, then. An object in motion will tend to remain in motion. An object at rest will tend to remain at rest. Unless acted on by an external force. In this situation, momentum is conserved, and the change in the momentum is zero. P is a letter for momentum, so the change in the momentum, the delta P is equal to zero. That change. If the change in momentum is not zero, then a force is acting, and we'll come to that in just a moment. Here, the ball is in motion, at a constant velocity being maintained by the constant speed of the lipstick. For the camera man, the ball is conserving momentum. The momentum is not changing for that ball. It is constant, it is non-zero, and it is not changing. The momentum of the ball is conserved, but what about for the rider, the rider on the lipstick, is momentum conserved for the ball from their point of view. And the answer is yes, the person on the lipstick sees the ball as stationary, has a velocity of zero, is not moving. The person on the lipstick says the momentum is zero, and stays zero. There's no change in the momentum. So both the cameraman and the rider say that momentum is conserved. They just don't agree on what that constant value of momentum is. Newton's second law is that the change in momentum is proportional to the force that has acted, the external force. In this case, the momentum of the rider in the ball comes to a stop when the rider hits the wall. More accurately, the lipstick comes to a stop. Both the rider and the ball continue on because there's no external force acting on them. The external force is actually acting on the lipstick itself. So the change in the momentum is equal to the force acting on it, and external force changes momentum and the two are proportional to each other. Newton's third law is that for every force, there's an equal and opposite counter force. The force of the lipstick and the basalt rack is equal and opposite to the force of the basalt rack and the lipstick. They both hit each other. So Newton's third law is that for every force, there's an equal and opposite counter force. The force of the bucket on the ground is equal and opposite to the force being exerted back on the bucket by the ground as that bucket is dragged along the ground. There are these force pairs always at work. That's Newton's third law.