Set the cookie tray on the floor in front of a sturdy chair. Stand on the chair, and hold the golf ball and the tennis ball at the same height. Drop the balls at exactly the same time. If you can, try the experiment again, holding the feather in one hand and a golf ball in the other. The tennis ball and the golf ball hit the ground at the same time.
Gravity pulls objects down to Earth at the same speed, regardless of how heavy they are.
The feather, on the other hand, falls more slowly than a golf ball. But not because the feather weighs less than the ball. The air in the room pushes against the feather, making it float down slowly rather than fall quickly. Interestingly, if you drop a feather and a golf ball on the Moon, they WILL hit at the same time. There's hardly any air on the Moon, and just like Earth, the Moon's gravity pulls objects down at the same speed.