Archives of Ask A Scientist!
About "Ask A Scientist!"
On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.
Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.
Water droplets are carried from the bottom of the cloud to the top by the strong updrafts. Eventually they pass through the freezing level and the droplets will begin to freeze forming an outer thin shell. The positive charges within the water droplet migrate to this thin ice shell. Turbulence is generated within the cloud and this causes the partially frozen droplets to collide, shattering the outer ice shells. Since ice is less dense than liquid water, the ice particles will be carried higher in the cloud by the updraft, while the heavier liquid droplet, which may or may not freeze, will fall. This creates a charge separation within the cloud, with positive charges at the top and negative charges at the bottom. This thermoelectric effect is still disputed to some degree.
Another process, called induction, may contribute to charge separation. After a thunderstorm develops a positive charge at the top and negative near the bottom, an induced charge will develop on the ice crystals within the cloud. The negative charges will migrate toward the end of the crystal facing the top part of the cloud and positive charges toward the bottom part. As updrafts bring small droplets and other ice crystals upward, they will collide with the larger ice crystals. The particles will "bleed" off the positive charges and carrying them to the top part of the cloud.
Once the charge separation is established, the second phase occurs in a two-step process. The first part consists of a stepped leader. This is a negatively ionized particle channel about 10 cm (4 in) in diameter, which moves towards the surface, and develops many branches extending from a main channel. Each section travels about 50 m (165 ft) in a microsecond. The sections continue until they approach the ground where there is a strong buildup of positive charges at the surface in that region. The positive charges will move upward through various objects such as trees or people in an effort to reach the stepped leader. Once the distance between the stepped leader and the ground is small enough, the attraction force between the positive and negative charges will break down the resistance of the air allowing the positive charges to "jump" across the air to meet the descending stepped leader. Air in the channel heats to about 30,000 K (54,0000oF), which causes the air to emit visible light and expand rapidly. The visible stroke travels upward from the ground to the cloud and the rapidly expanding air creates the thunder. Usually more than one stroke is needed to neutralize all negative ions so another leader, or dart leader, is initiated and a return stroke follows. The process is repeated about four or five times on average to neutralize all ions resulting in a flickering of the lightning flash. Since the positive charges fill the entire channel, some of the branches of the stepped leader which have not come in contact with the ground will be filled-in, thus giving the appearance that lightning is traveling downward. Both phases are constantly renewed during the life cycle of the thunderstorm.
- Apparently Romer measured the speed of light due to a delay in the satellite of Jupiters orbits. But how did he measure it - he must have had a succession of measurements over say 1 year, yet been able to time very accurately the advance or retard. How did he do this since he didn't have an accurate pendulum clock. ie what was his actual experimental method - nowhere can I find a good description.
- What is lightning and what makes thunder rumble?
- What color is Saturn, and are there planets in other galaxies?
- If fire needs air to breathe and the sun is a ball of fire, how does the sun stay lit if there is no air in space?
- Why does the earth revolve around the sun in an oval shaped orbit not in a round orbit?
- How do they measure how far away stars are?
- What is a black hole and why does it suck in objects in space?
- What is a shooting star?
- If icebergs are made of fresh water, why don't they melt in the salt water of the ocean?
- Why don't explorers go to planets other than the moon?