When a person steps on something sharp (like a nail), the leg that is stepping on the nail reflexively pulls away (the flexor muscles contract and the extensor muscles relax), while the other leg reflexively takes the weight of the whole body (the flexor muscles relax and the extensor muscles contract) in preparation for the jerk.
A molecule is the smallest particle of a substance that exists independently. Molecules of most elements are made up of only one of atom of that element. Oxygen, along with nitrogen, hydrogen, and chlorine are made up of two atoms. Look at the model of oxygen above. The two balls represents the two oxygen molecules.
Answers. 1  A quark is a particle found in protons and neutrons. Their mass is unknown, but they are the smallest subatomic particles. 2  Aerogel a.k.a blue smoke is the lightest most expensive thing on earth. 3  The lightest stable gas is Helium gas. Lightest solid is Aerogel, which weighs .0003 g/cm3.