What causes a low or high tide?
The high and low tide are caused by gravitational forces between the liquid surface of the earth and the moon. As the moon pulls water towards itself it pulls it away from the opposite side of the earth. This creates high tides at night, and low tides at noon when the moon is on the opposite side of the earth.
Knowing that 1 mole = 6.022x10^23 particles, what information would you need to calculate how many particles/molecules are in a 50 g sample of NaCl?
To calculate how many molecules are in a 50 g sample of NaCl I would need the atomic mass of Na and Cl to determine the molar mass of the molecule.
How does Newton's First law apply to the interaction between my feet and the floor that I am standing on?
According to Newton's First Law of Motion, an object at rest will remain at rest an object in motion will remain in motion unless acted upon by an opposing force. Therefore when I stand on the floor I am applying force to the ground. This is due to my mass and gravity pulling on myself and the atmosphere above me, but I do not sink into the ground due to the opposing force the ground is asserting on my feet.