# Units of mass and speed

Hello,
I just need to know in which units mass and speed are. I think mass is in kg, but i’m not sure.
Thanks
Turakar

kg and m/s

1 Like

thanks

In the SI system of measurement (the International System of Units), the fundamental unit of mass is the kilogram. A smaller unit, the gram, is also used widely in many measurements. In the English system, the unit of mass is the slug. A slug is equal to 14.6 kilograms.

Scientists and nonscientists alike commonly convert measurements between kilogram and pounds, not kilograms and slugs. Technically, though, a kilogram/pound conversion is not correct since kilogram is a measure of mass and pound a measure of weight. However, such measurements and such conversions almost always involve observations made on Earth’s surface where there is a constant ratio between mass and weight.

Correct me if I’m wrong - but I think that only place where it is actually observable is default value for gravity (-10)? And that is only for unit of length - is there ANY place where unit of weight matters? I think that you can just assume that 1 = 1 ton and everything will work?

For example if you’d like to calculate outside of Bullet what forces to apply then it might matter. But mostly it is an interpretation in the application.
http://www.bulletphysics.org/mediawiki-1.5.8/index.php?title=Scaling_The_World

It matters also in how it relates to the size of the object. 1 cubic meter at 1 kg is going to behave differently than 1 cubic meter at 1 ton.

…and it matters to more than just gravity in that case because collision restitution will be based off of the relative mass of the objects. I mean, it’s all relative… but I’d be very surprised if behavior was the same for 1 kg versus 1000 kg.