A football player runs 30 m east and then runs 40 m west. What is the distance that the football player ran?

What are similarities and differences between refraction, reflection, diffraction and absorption?

At very high pressures, gases become and will eventually a) more dense; become hotter b) more dense; change to a liquid or solid c) less dense; combust d) less dense; turn into a liquid

The softest and hardest minerals are: softest hardest