Okay so I was going through my calculus textbook and I am stumbled on the WORK section. Here it says work=force*distance, and force=mass*acceleration. In a problem they use gravity for acceleration which I guess you can do. So they have: F=mass*gravity So to calculate the WORK they use that Force and multiply it by the distance. The mass they have was in kilograms. Then, in a similar problem they have weight which is in pounds. They say F=the pounds, because weight is a force and not the mass of the object. Then they just multiply the pounds by the distance to get the WORK. So they don't multiply the pounds by gravity. So my question is: how do you tell the difference between mass and weight by looking at the units? Up until now, I always thought weight=mass. That's the reason why I thought we can change the units of pounds into kilograms. If kilograms=mass and pounds=weight (where weight is a force and mass is matter in an object), why can we change the units by multiplying/dividing either kilograms/pounds by some constant (I don't know the constant but I know that it can easily be found by using Google :D)? Also, why is weight a force and mass just mass? Note: I have not taken physics yet; I am taking chemistry in school. So I knew that F=mass*acceleration from middle school, but I am not thoroughly well known that work=force*distance so that stuff is pretty new to me. So please try to explain this stuff as simple as possible XD. Thanks and have a great day!