Newton's Laws of Motion and Newton's Law of Gravity explain why? a) the Earth moves around (orbits) the Sun.
b) the Moon moves around Earth
c) an apple from a tree falls down to ground (as opposed to "rising up into the sky")
d) all of the above

Large electric fields in cell membranes cause ions to move through the cell wall. the field strength in a typical membrane is 1.0 x 10 7 n/c. what is the magnitude of the force on a calcium ion with charge +e? what is its acceleration? is it possible for a particle with the same charge as as calcium to have a different acceleration if placed at this location? what would change the acceleration: mass of the particle? diameter of the particle?