Science a GoGo's Home Page Forums General Discussion Physics Forum Flatness Problem: To call a spade a spade.

I thought up a simple example.

in space where there is no gravity.

two bullets traveling towards each other.

they each have a mass of 2 kg

if they did not have motion their mass would be 1 kg each.

because they have motion their combined mass is 4 kg

when they collide they stick to each other and all of the
kinetic energy is lost.

the two bullets are now stuck together but are motionless.

they now have a combined mass of 2 kg.

2 kg mass was lost because the kinetic energy was lost.

thats pretty easy to see.