In the 1640s, the flemish chemist jan baptista van helmont performed the classic experiment paraphrased below: i filled a pot with 200 pounds of dirt that had been dried in an oven. then i planted the stem of a willow tree and watered it with rainwater. at the beginning, the willow stem weighed 5 pounds. for 5 years, i watered the tree with either rainwater or distilled water whenever it was needed. the pot was large, and planted in the ground. i covered the pot with an iron plate. this had many holes, which allowed water through but not dust. in this way, i could be assured that possible dust accumulation over these 5 years did not significantly add to the weight of the dirt. after 5 years, the tree weighed 169 pounds, and about 3 ounces. i did not take into account the weight of the leaves that fell each autumn. at length, i again dried the dirt, which weighed only 2 ounces less than the initial 200 pounds. i concluded that the 164 pounds of wood, bark, and roots, arose out of water only. in what way was van helmont's conclusion incorrect?

Comedians like to joke that the reason we haven’t been visited by intelligent life from elsewhere in the universe is that aliens have been monitoring earth’s broadcasts of intellectually embarrassing tv programs, like gilligan’s island, fear factor, the jersey shore, and the jerry springer showand so consider us far too primitive to merit a visit. let’s check the assertion that aliens could have been receiving them. tv programs are broadcast at a frequency of about 100mhz with about 100kw of total power in 30frames per second, which emanatesroughly uniformly in all directions. assume that interstellar space transmits these broadcasts without attenuation. no matter how smart they are, aliens would require at least one photon per frame to interpret our signals. findthe number of photons per unit time per unit area reaching a receiver on a possible planet in the nearest star system, which is about 4 light-years away (a light-year is the distance light travels in a year). if aliens aimed a receiver or detector directly at earth, how big (in diameter) would it have to be to receive a photon per frame

10 newton object is placed 3 meters from the fulcrum. at what distance on the other side would you need to place a 15 newton object to balance the lever? show your work!

The movement of electrons between atoms is called an