Answers
1. How come a boomerang comes back when you throw it ?
The shape of a boomerang's arm is what brings it back. On one arm (like a wing) it is curved and points up. The other one points down and curves away from the wind. It lifts and turns like and airplane wing
2. Why do you throw a boomerang vertically instead of horizontally like a frisbee ?
To help the boomerang travel in a big circle. The flat side points away from you. It turns because of the way the wind travels over its arms. It lifts on one side and that makes a turn.
Reference from: How Come by Kathy Wollard