Question

Should science teachers keep talking about the law of conservation of energy and the law of conservation of mass? The law of conservation of mass says that there is always the same amount of mass in the universe and the law of conservation of energy says that there is always the same amount of energy in the universe, but Einsteins proven (atom bomb) equation, E=mc2, the says that after fusion, there is less mass in the universe and more energy in the universe. What do you think?

Answer 1

That is why E=mc2 is so profound. Both are conserved and can be transformed into one another.

Answer 2

In everyday experience conservation of energy, and conservation of mass hold.
Only under extreme circumstances, such as nuclear processes fusion in a star or fission in a bomb or power-plant does mass get converted to energy.

If such extreme circumstances are not present it is unnecessary to unite the energy mass conservation laws

Answer 3

You are missing a very curial part of the point. The equation \[E=mc^2\] is only half of the full equation and represents the intial energy given by the object solely by existing. The full equation contains both the Mass and the Momentum. \[E=m^2c^4 + ( pc)^2\] the implication that the total energy of the system is dependent on the mass and momentum of the object is what makes the equation so powerful. if your remove energy from your system it can either come from your momentum or our mass and vice versa. Note that in fussion the mass into the reaction does not equal the mass of the reaction, which is why you have an energy release due to the binding energy of the nucleus.

So yes, both conservations laws are prefectly acceptable to teach at the high school level.

Answer 4

Teachers should say mass is conserved, except in nuclear reactions.

Answer 5

The Law of Conservation of Mass is sort of like a sub-law of the Law of Conservation of Energy. Einstein's equation shows that mass and energy are equivalent. Just like kinetic energy, potential energy; mass is just another form that energy can take. While it's true that mass is not conserved in nuclear reactions, most people won't need to consider this case. In the same way, car manufacturers don't need to take relativistic effects into account in their velocity calculations because they aren't noticeable at car speeds. For that reason, the mass law is definitely worth teaching, not least because reactions in chemistry and biology rely on it being (effectively) true.