What is Rest mass?
'''Rest mass''' (physics), the [[mass]] of something that is not moving. All [[matter]] has some rest mass. [[Energy]], such as light or kinetic energy (the energy of a moving object) has no rest mass because it causes no change in [[spacetime]] in a frozen time frame. However, energy affects mass while time passes; therefore, it affects spacetime, so it has mass.<ref>{{cite web |url=http://www.physlink.com/Education/AskExperts/ae161.cfm |title=What is rest mass? How to explain it especially to the high school students? |access-date=2009-10-06 |publisher=PhysLink }}</ref> ==References== {{reflist}} {{physics-stub}} [[Category:Relativity]]