Why are scientific theories modified and not just thrown out when new evidence is discovered? this is 8th grade science by the way

When a spring is compressed, the energy changes from kinetic to potential. which best describes what is causing this change?

What type of electromagnetic radiation has a shorter wavelength than blue light

Nebulae are enormous clouds in outer space. they are made mostly of hydrogen gas, helium gas, and dust. some nebulae glow brightly, while others do not. the stars that people see are huge, bright balls of glowing gas. they are made mostly of hydrogen and helium. which statement correctly describes other ways in which nebulae and stars are different? a. stars can form inside a nebula but a nebula can never be produced by any star. b. a star always has a higher density than a nebula. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star.