Speed is a relative concept. It depends on a fixed reference. When someone says that a car runs at certain speed we know it assumes that the earth is static. Based on a static earth, that car runs at certain speed. If the speed of any object depends on the fixed point of the observer you can have a lot of fun when you try to imagine what different observers see in terms of time, distance and speed when you focus your attention to what happens to certain objects.

Try to imagine what happens to a ball that drops to the floor inside of a crystal train (so you can see inside the train) that is running at 100 kilometers per hour. The ball falls in straight line from the perspective of a person sitting in front of the table where the ball falls but an observer standing outside of the train, looking at the train going by, he would see that the ball is not falling vertically in a straight line. If the table is 1 meter tall and it takes 1 second to fall, what is the distance- in a straight line- from the initial point in the table to where the ball hits the floor of the train from the perspective of the observer outside of the train? The only formula you need to know is that the speed of an object equals the distance of its trajectory divided by the time it takes such trajectory. The speed of the falling ball is 1 meter per second from the perspective of the person inside of the train.