# Different between mass and drag

Would love to know the different between mass and drag. My understand for mass is weight of object while drag for air resistance, so the smaller value of of drag the object will fall faster. But, I am confuse as I thought mass (weight) will decide the speed of the falling object, why there’s need of drag.

Thank you

Mass is the resistance an object has to changing its speed. Think of two skaters gliding toward you on an ice rink. One is a tiny little girl. The other is Mike Tyson. They are both going the same speed, but they have different masses. It takes much less force to stop the little girl than it does Mike Tyson. This has nothing to do with friction or air resistance - it is just a property of their different masses.

Now think of them both jumping off a high dive board into a swimming pool. Which one would hit first? If you ignore air resistance for a moment, then it turns out they they hit at the same time. Galileo is credited with discovering this. Why doesn’t Mike fall faster? Its because the force of gravity is proportional to your mass, so the force on Mike is greater by exactly enough to make him accelerate at the same rate as the little girl.

O.K. so that is mass. Now we can speak of drag. Drag is an additional force (unrelated to gravity). You can think of drag as air resistance, friction from being drug through sand, or anything else that slows you down. But in Unity it is a force proportional to -velocity * mass. This means it is also independent of mass (meaning it creates the same acceleration on two different masses), but dependent on velocity. The faster you are going, the more drag. Drag in Unity operates something like friction, but not like air resistance.

Just remember, gravity affects mass not drag. Set gravity to 0 and objects will not fall no matter what the drag value is.

Mass doesn’t actually determine the speed of a falling object, only the force of it. The reason that objects fall at different speeds is the difference in air resistance.