Excerpt from
The Jensen Family

Probably he got caught in a steel trap like this one over here," their dad said, pointing to an exhibit in the next case.
"But how could he get free from that?" Julie asked.

Continue Reading...

– posted 12.04.2009

#74: Tides Can Teach

A Character story about dependability.

One summer the Jensen family were able to take a quick trip up to the Bay of Fundy in New Brunswick, Canada.
"When are you going to get there?" Jason asked impatiently. "I can hardly wait."
"Me, too," Joshua agreed.
"Just a few more minutes," Mr. Jensen assured them as the car rounded another bend and climbed another hill.
"A whole day at the beach!" Julie squealed. "I can hardly believe it."
"And we'll be arriving at just the right time," Mrs. Jensen remarked. "The high tide in this part of the Bay of Fundy is about a hour away. There will still be some beach, and if we stay until supper time, we'll be able to see both the high and low tides."
In no time at all, the family was clopping down the stairs toward the water, loaded with the picnic supplies.
"Let's take off our shoes and walk out to the edge of the water," Mr. Jensen suggested. Everyone was glad to oblige, especially Joshua. "Now let's see how high the water rises in one minute. Everyone stand still. Ready, go."
When a minute was up, Julie commented, "That rock there was completely out of the water but now it's half submerged."
"Yah, it sure does rise fast. How high will it get?" Jason asked.
"Look along the shore. You can see the deposits from other high tides. Today it won't reach the highest mark but by next week the tide will rise over 50 feet."
"Fifty feet?" Julie exclaimed. "How much is that a minute?"
"Well, let's see," Mr. Jensen mused, plopping down on a rock and pulling out his pocket calculator. "Fifty feet in 6 and a half hours would be . . . ah . . . 92 inches an hour which would be about an inch and a half every minute."
"Wow! But how can you tell it won't rise the highest today?" Jason wondered.
"Did you see the moon this morning? It was just about at third quarter. The highest tides are at the new moon and full moon."
"Really? Why is that?" Jason wondered.
"Let me show you," Mr. Jensen said, picking us two rocks. "Let this rock be the earth and this one the moon. Jason, you be the sun."
Jason grinned. "I've been the son all my life. That's why I'm so bright."
"I could see that one coming," Julie groaned.
"Regular typecasting," Mr. Jensen quipped. "Anyway, tides are caused by the gravitational pull of the moon upon the earth. The earth's gravity holds the moon in orbit around itself, but the moon also has a pull on us. As the earth rotates each day, like this, the gravitational pull of the moon moves across the earth and whatever is in that line gets a tug."
"So why does the tide rise and fall twice each day then?"
"The line of gravitational pull goes through the earth. So when the moon is closest and farthest from us, the tide is at the highest point. Let's scratch a line on this rock. Now imagine we are standing on that line on earth. Now imagine a line from the moon through the earth and beyond. That is the gravitational pull. As the earth rotates one complete turn, how many times would we pass through that gravitational line?"
"Twice," Julie answered.
"Right. That's why there are two high tides and two low tides in a little over 24 hours. People living a fourth of the way around the world from us are getting the low tide while we are getting the high, and vice versa."
"But why is the high tide a different time every day?" Jason wondered.
"Good question. There are other factors taken into consideration in predicting the tides. For example, since the moon is also going around the earth in the same direction, it takes a little longer than 24 hours for us to be right in front of or behind the moon again. In fact, high tide comes every 12 hours and 25 minutes and it takes an extra 50 minutes to get the high tide by facing the moon again."
"I think I understand that," Julie announced. "The moon kind of like runs ahead a little from where we last saw it a day before."
"Right. It runs ahead 12 degrees of his orbit to be exact. It takes us 50 extra minutes each day to meet it at its new position."
"Aren't you forgetting something?" Jason asked. "What about your favorite sun, S-U-N, of course."
"I'm not forgetting," his dad assured him, "but to answer your first question, you needed to understand all this. You see, though the moon's pull is much stronger, the sun also has a part in causing tides. When the sun and moon are both on the same gravitational line, like this, they work together to increase the pull, and the tides are the highest. These highest tides are called spring tides and come when the moon is on the same side as the sun- that's a new moon- or the opposite side- that's a full moon. When the moon is at its first or third quarter, the sun is at a 90 degree angle with the earth and is working against the moon's pull. These smaller tides are called neap tides."
"But if the sun is so much bigger than the moon, why is the moon's pull stronger?" Julie asked.
"I know that," Jason announced. "Because the moon is so much closer, right Dad?"
"Right. Because of this, the moon exerts more than twice the pull of the sun. Here in the Bay of Fundy, the low tides are about 40 feet, but for the high tides, the sun and moon work together to lift the water over 50 feet twice a day! those are the highest tides in the world."
"How many gallons of water would that be?" Julie asked. "A trillion?"
"I don't know that one," Mr. Jensen answered, "but it would be a lot. I read somewhere that 100 billion tons of water a day are moved about in this bay. If a gallon of water weighs about eight and a third pounds, then you can figure out how many gallons that is."
"No thanks," Julie snickered.
"It takes a lot of energy to move that much water back and forth. In a few places in the world, power plants have been built to harness that energy to produce electricity. In fact, one such plant is on the other side, in Nova Scotia."
"Anyone for lunch?" Mrs. Jensen called.
"Sound's great," they all agreed.
After giving thanks for their food, Mr. Jensen remarked, "Several years ago now, I heard a famous man say that if God didn't let him into heaven, he would hold a protest march before His throne. However, that man refused to believe what God had told him in the Bible. I think of that man when I see something as powerful and predictable as the tide. If he stood at the low tide mark and had a protest march about the tide coming in, what do you think would happen?"
"I think he'd be drownded," Julie answered.
"I agree. Yet some people seem to think they are almost as big as God. If we can do nothing against a small display of His power, what will we do in His presence? I'm sure of one thing: there will be no protest marches before the throne of God. What He has said in His Word will come to pass. Nothing in heaven or earth can stop that."
- - - - - - - - - - - - - - - - - - - - - - -

PUZZLE FOR THE MATH MINDED (See if you can figure this out without using a Tide prediction chart.) If the high tide were at 12 o'clock noon on September 1st, it would be 25 minutes later for the next high tide (September 2nd at 12:25am), 50 minutes later on the next one (12:50pm on the 2nd), etc. On what day and month would the next high tide arrive at 12 o'clock sharp? Would it be at noon or at midnight? (full answer next time)