Some objects are heavier then others because they have more mass. Exp: A bowling ball has more mass then that of a feather. A person has more mass then that of a bowling ball. And so on…
Here's a quote to help!
"Galileo discovered that objects that are more dense, or have more mass, fall at a faster rate than less dense objects, due to this air resistance. A feather and brick dropped together. Air resistance causes the feather to fall more slowly."