In F.2 the key idea that I talked about was Newton's Second Law. This concept is brought up again in F.4 in order to help explain Newton's third law. All the units of the chapter build upon each other. The concepts are expanded each unit and become clearer and add more concepts each time. The chapter helps to explain this new concept by bringing up a concept that we have already learned. F.4 started by stating that Newton's third law is when one object exerts a force on a second object, the second object exerts a force on the first object that is the same strength, but in the opposite direction. It then goes on to give an example that was used in the initial ideas of F.4. The example is talking about a small truck and a big truck. The trucks collide with each other. During a collision between a big truck and a little truck, the force pair is the force the big truck exerts on the little truck and the force the little truck exerts on the big truck. Newton’s Third Law says that these forces are equal in magnitude (size), but act on different objects and in opposite directions. To understand how the trucks accelerate differently, it is necessary to think about Newton’s Second Law. Since the two forces are the same (F Big Truck = F Little Truck), we can just compare their masses and accelerations (m⋅a Big Truck = m⋅a Little Truck). Since their masses are different, we know that their accelerations must also be different. The mass (m) is much greater for the big truck and the acceleration is much smaller for the big truck. This is why the little truck slows down so much more quickly in the accident than the big truck. F.4 mentions again how mass affects acceleration like it was explained in F.2. This time it is used to expand the concept of Newton's third law and how two objects will have equal and opposite reactions in different directions. The biggest difference between the two concepts is that newton's second law was talked about using two carts moving in the same direction so we could compare them, while newton's third law was talked about with two carts hitting each other in a collision. The difference is talking about the effects on one object compared to the effects on two objects.One similarity is that we did use two carts in each experiment. We also used weights in order to look at how mass affects acceleration in both cases.