【阅读选择】On the other hand, on the moon there will be an attraction between the butter and the moon; but the butter will weigh only about one-sixth as much as it does on the earth. This is because the moon is so much smaller than the earth. The amount of gravitational pull that a body produces depends on the amount of material in it. A packet of butter has a gravitational pull of its own; but this is very small in relation to the pull of something as large as the moon, or the earth, or the sun. We do not feel the gravitational pull of a packet of butter because ______.