如图甲所示，放在水平地面上的物体，受到方向不变的水平拉力F的作用，其F﹣t和V﹣t图象分别如乙、丙所示，由图象可知，当t=1s时，物体受到的摩擦力是____N，当t=3s时，物体受到的摩擦力是____N。

    This is Jim. He is thirteen. He is from the USA. He is a student. He has a good friend. His name is Jack. Jack is fifteen. He is from Canada. Jack is tall but Jim is short. They are in the same class, but they are in different grades. Jim is in Class Two. Jack is in Class Two, too. They go to school(上学) at seven in the morning and go home(回家) at six in the afternoon.

本特利在《新全球史》评论道：近代某科学家将天体、地球联系在一起，并放到整个宇宙体系中进行研究；开创性地提出整个宇宙中的物体都遵守的一个定律，并运用数学推理予以证明。该科学家（    ）