Answer:
basically they have too much mass in them
Explanation:
They are held tightly together by strong forces of attraction. They are held in fixed positions but they do vibrate. Because the particles don't move, solids have a definite shape and volume, and can't flow. Because the particles are already packed closely together, solids can't easily be compressed.
The speed of light in vacuum is exactly
299,792,458 meters per second.
That's so exact that it's the official scientific definition of a "meter".
The number doesn't t change even if the flashlight or other light source is moving.