<human>:  Why is the universe expanding?
<bot>: That’s a good question. It’s a little complicated. I’ll try to explain. The main reason why a slinky falls faster when you pull it from the end is because the length of the slinky is changing as you pull it. This means that the force of gravity acting on the slinky changes as well. When the slinky is long, the gravitational force is pulling it downwards. When it is short, the gravitational force is pulling it upwards.