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Bellringer • What causes lightning?
Objective • Explain what causes lightning.
Lightning Video • http://video.pbs.org/video/1615154986/ • How do scientists get better information on lightning strikes? • What do scientists believe triggers lightning strikes? • What evidence is there to support this theory?
Where is Lightning? • Lightning is most commonly developed within a thunderstorm • Lightning has also been seen with in volcanic eruptions, heavy snowstorms, and in large hurricanes.
Formation of Thunderstorms • A thunderstorm forms in air that has three components • Moisture • Instability • Something such as a cold front to cause the air to rise • The rising motions within the storm can build a cloud from 6 to 10 miles above sea level.
Formation of Lightning • At this elevation temperatures are much colder; so ice begins to form in the higher parts of the cloud • As the falling ice and sleet collides with the rising moist air, it picks up extra electrons from the ice and sleet. • The ice and sleet then deposits these electrons at the bottom of the thunderstorm cloud.
Formation of Lightning • The separation of charge is crucial for lightning to form. • The separated charges cause the bolts of lightning we see. • The more charge that is separated the bigger the strike.
Bellringer • What do scientists currently believe is the mechanism for triggering lightning strikes?
Objectives • Review the tornado quiz • Investigate how separating electric charges can produce electrical sparks similar to lightning bolts so we can explain the phenomena.
Tornado Quiz • Class average was 85
Separation of charge?? • What does separation of charge mean? • Atoms are normally neutral (meaning they have no charge) • However you can remove electrons from certain atoms and put them somewhere else.
Separating Charge • Some atoms (typically metals) don’t care about all of their electrons so they can be removed or shared with another atom. • How can you remove extra electrons from an atom?
Separating Electrons Demos • Balloon Demo • Opposites Attract Demos • Likes Repel Demo • Sparks Demos
Bellringer • How is static electricity built up in a thunderstorm cloud? • The falling ice collides with the moist rising air to transfer electrons to the bottom of the cloud. Thus leaving the top of the cloud with a positive net charge.
Objectives • Know the differences and similarities of CG, CC, and IC lightning strikes. • Understand the frequency of lightning strikes around the world. • Know what causes thunder and be able to calculate your distance from a lightning strike based on the time delay of thunder.
Lightning • Lightning is approximately 50,000 degrees Fahrenheit • The average lightning bolt is hundreds of millions of volts and typically about 50,000 amps
Types of Lightning There are two types of lightning • Cloud to Ground – 10% • Cloud to Cloud or Intra-Cloud – 90% • CC and IC lightning are far more common than CG lightning, but CG lightning has a greater effect on humans so more research has been done on that.
Cloud to Ground Lightning • As a thundercloud moves over the surface of the Earth it induces a positive charge on the surface. What happens to the taller objects? Can you become the tallest object around?
CG Lightning • These two oppositely charged objects create a strong electric field. • An electric field stores energy that can be released at a later time. Similar to a battery. • Once triggered this energy is released in the form of a lightning bolt.
CG Lightning • Normally air is an insulator and will not let electrons flow through it. • When enough energy is applied a path to Earth becomes “ionized”. • This ionized path is light a highway for the electrons to travel on.
CG Lightning • Once the bottom of the cloud and the Earth’s surface are neutral again, the ionized highway closes down. • While that path of air is ionized, the air acts as a conductor instead of an insulator.
Flash of Lightning? • Lightning seems to happen is one bright bolt but is that really what happens? • Let’s take a look: • https://www.youtube.com/watch?v=JVXy-ZqqZ-g
CG Lightning • Why does the main lightning bolt seem to pulse in slow motion? • It takes the electrons a few moves from cloud to ground and back to cloud until they are evenly distributed.
Cloud to Cloud and Intra Cloud • This is more common than CG lightning, but it doesn’t cause nearly as much destruction because it doesn’t hit anything or anyone. • It also won’t appear as bright or as loud because it is buried in the cloud, and typically further away than CG lightning.
Cloud to Cloud Lightning • CC lightning occurs between two separate clouds. • The lightning process is the same as CG, but it between a negative part of one cloud and a positive part of a different cloud.
Intra-Cloud Lightning • IC lightning is when a lightning bolt strikes within one thunderstorm cloud. • Lightning bolt between the positive top and negative bottom of the thundercloud. • This is even more common than CC lightning because the particles in the thundercloud make it easier to conduct electricity.
Checkpoint • Explain the differences between CG, CC, and IC lightning strikes. • How are CG, CC, and IC lightning strikes similar?
Frequency of Lightning Strikes • On Earth, the frequency of lightning is approximately 40 to 50 times a second! • That’s nearly 1.4 billion flashes per year! • Lightning strikes everywhere on Earth, but is more common on land over the tropics (70%)
Lightning Capital of America • Florida sees more lightning than any other area in the USA • Lightning Alley is from Tampa to Orlando • As many as 50 strikes per square mile a year • The Empire Stat Building is struck on average 23 times each year • Was once struck 8 times in 24 minutes
Lightning In America • This website tracks every lightning strike in America… • http://www.weather.com/maps/activity/golf/uslightningstrikes_large.html
Thunder • Thunder is the sound caused by lightning • It is so loud because it is a sonic boom. • Meaning that it has so much energy that is causes the air particles to move faster than the speed of sound • Thunder IS NOT the collision of clouds. There must be lightning for there to be thunder.
Thunder • The distance of the lightning can be calculated by the listener based on the time interval from when the lightning is seen to when the sound is heard. • The lightning is approximately one mile away for every 5 seconds between sound and flash.
Storm Watch • How far away is the lightning bolt if you see the flash and the 15 seconds later you hear the thunder?
Summary • Why does CG lightning typically hit the tallest object in the area? • What state has the most lightning strikes? • What causes thunder?