Lightning and Thunder Time Differential Can Determine Distance: Flash-to-Bang Method

Posted on September 12th, 2015 by kramer

Twice this summer, I experienced severe lightning storms on the water. Understanding this natural phenomenon can make this experience fascinating and safe instead of scary. Since the sound travels at 1,088 feet per second, it takes five seconds for bang of thunder to travel one mile. So counting from the flash to the bang and dividing by five will tell you the number of miles that lightning is from your location. The major math objective of this lesson was to teach children special strategies for dividing by five. 

 

Here are the scientific objectives of this lesson:

 

  1. Static electricity is the cause of lightning.
  2. Lightning forms because of an accumulation of electrical charges inside a cloud due to friction from dust, ice, and water droplets. 
  3. The bottom of a cloud becomes negatively charged and discharges a lightning strike when enough charge has built up. 
  4. Lightning causes thunder by heating the air to 50,000 degrees Fahrenheit (about 5 times hotter than the surface of the sun).
  5. This extreme heating causes the air to expand at an explosive rate; this expansion creates a shock wave that turns into a booming sound wave called “thunder.”
  6. Lightning and thunder happens at roughly the same time although you see the flash of lightning before you hear the thunder.
  7. Light travels at 186,291 miles per second.
  8. Speed of sound is 1088 feet per second.
  9. Light is almost 1 million times faster than sound (actually, 904,059 times faster).
  10. One mile is equal to 5,280 feet. So, in five seconds, sound travels 5,440 feet or a little more than one mile.
  11. In order to determine the distance from a lightning strike to your location, after the flash, count the number of seconds until you hear the thunder. Divide this number of seconds by 5 to get the number of miles.
  12. To accurately count seconds, recite in a rapid pace, “1 One Thousand, 2 One Thousand, 3 One Thousand, 4 One Thousand” and so on. Use a stopwatch or second hand on your clock to practice the timing of your counting.
  13. SAFETY RULE OF THUMB IS “WHEN THUNDER ROARS, GO INDOORS.”
  • when you hear thunder within 30 seconds of the flash, the lightning is 6 miles away; go indoors until the difference is greater than 30 seconds
  • avoid open fields or the top of a hill
  • stay away from tall isolated trees or other tall objects; stay near low trees.
  • stay away from water and metal objects (fences and poles); they do not attract lightning but they are great conductors of electricity
  • if you are on a boat without a cabin, get to land and a shelter
  • if you are on a boat with a cabin, stay inside and away from metal surfaces
  • if you are scuba diving, you are safe if you stay deep in the water through the storm

For example, if the thunder is heard 30 seconds after the lightning flash, you need to divide 30 by 5 to determine how many miles away the flash is from your location.

Multiples of 5 Method (K-2nd Grade): You can always just count by five until you reach your number. 5, 10, 15, 20, 25, 30. Using your fingers, you now have 6 so 30/5 = 6. The lightning is 6 miles from your location — go inside.

 

Double the Tens Method (3rd-7th Grade): Circle the digits to the left of the units digit. Since “0” is the units digit, you will circle the “3” in 30. Now double that number: 3 + 3 = 6. Why does this work? There are two 5s in 10 and there are 3 tens in 30; so 3 X 2 = 6.

 

1. What if you are dividing 120 by 5, you will circle the 12 and double which is 24; so 120/5 = 24.

 

2. What if you are dividing 125 by 5? Again, circle 12 and double which is 24; but you have a remainder of 5 (how many 5s? one five); so add one more 5 to the solution; so instead of 24, the solution is 25; 125/5 = 25.

 

3. What if you are dividing 123 by 5? Again, circle 12 and double which is 24; but you have a remainder of 3 (that is not quite one 5). In fact, it is 3/5ths of one; so the solution is 24 and 3/5; 123/5 = 24 3/5.

 

4. What if you are dividing 127 by 5? Again, circle 12 and double which is 24; but you have a remainder of 7 (that is one more 5 plus 2/5); so the solution is 25 and 2/5; 127/5 = 25 2/5.

 

5. Let’s try to divide a four digit number by 5. We will try 1,010 divided by 5. Circle all of the digits to the left of the units digit “0” which is “101” and double it to get 202; so, 1,010/5 = 202. 1,015/5 = 203 1,014/5 = 202 4/5 1,016/5 = 203 1/5

 

The scientific objectives and dividing by five methods are summarized in the Flash-to-bang pdf below. There is a pdf which will give children from K-2nd grade practice counting by multiples of 5 to 570. 3rd graders may also want to try this challenge. 1st and 2nd graders have a pdf for using the Doubling the Tens Method for Dividing by five. There is another pdf with the Doubling the Tens Method for Dividing by Five, the last two pages of which are rather difficult but manageble by 5-7th graders. Have fun.

AttachmentSize
Lightning_and_Thunder_Flash-to-Bang_Method.pdf56.07 KB
Multiples_of_Five_to_570.pdf159.41 KB
Dividing_by_Five_1st-2nd_grade.pdf58.63 KB
Dividing_by_Five--3-7th_Grade.pdf288.93 KB