THE SLED:   A MATTER OF SOME GRAVITY   

                                Kathy Dullea Hogan, 2013

Once upon a time there was a little girl named Katherine.  Katherine’s father took her to a hill nearby so that she could go sledding down the little hill. 

Now, anyone who has enjoyed riding on a sled knows this:  You have to do some work first before you can coast down a hill.  Katherine had to climb up the hill, pushing down the snow with each step, and pulling her sled behind her.   Well, for the first ride her father pulled it for her.  He showed her how to sit on the little sled with her feet out in front.  He gave her the rope to hold on to.

“Are you ready, Katherine?” he asked. 

“I’m ready, Daddy!”

“Okay, then, off you go!” he said as he gave the sled a little push. 

The sled began to move slowly, then a little faster.  Katherine was excited and shouted, “Whee!” as the little sled went even faster.

 

As she reached the bottom of the hill and the sled came to a stop, she turned her head and found Daddy there, too.  He had run down the hill.   “Do it again,” she shouted, turned around, and started pulling the sled up the hill, by herself this time. 

Well, up and down that hill she went over and over and over.     She did a lot of work each time to climb that hill, but the ride down was so much fun -– no work,  she loved to shout “Whee!” on the way down. 

Finally -- it was time to go home and get ready for supper.  On the way home, Katherine told her Daddy, “That was fun!” 

“It sure was.  Do you know why it was so much fun to go down the hill, Katherine?”

“No, Daddy, why?”

“Because of gravity.  Gravity pulls you downhill.”

“I didn’t see anything pull me.”

“That’s right, you can’t see it.  But it’s there.  It’s like the air, it’s like the wind.”

“Like the wind?” 

“That’s right.  You see the leaves blowing when the wind blows, don’t you?   But you can’t see the wind.”

“Oh.”

“So gravity is something like the wind.  It’s there.  But you can’t see it.  You can feel what it does.”

“Oh.” 

“It pushes down.  It makes it easy to go down the hill -- and harder to go up the hill.”

“I know.  It’s hard to go up.  But on the way down, it’s not, it's easy,” Katherine said.

“That’s right, Katherine, very good.”

By now they had arrived at the corner of their street, Ocean Street.  Katherine’s friend Lois was in front of her house, two doors away from their house.   The two little girls started talking. 

Daddy told Katherine she could talk to Lois but then to come home right away. 

When she heard her mother call her, she said good-night to Lois and ran home. 

She went home and forgot her sled!

At home she had supper and told everyone  about all the fun she had coasting down the hill.  Later on, Mommy read her a story, then she went to bed.

The next morning she woke up and got dressed and asked if she could go coasting again.  As soon as she said it, she remembered that she had left her sled down the street.   

“Mommy, I left my sled outside.  Can I go get it?” she asked.

 

“Where is it?” 

“Oh, it’s near Lois’ house.”

“Oh, dear.  Well, go and take a look.”

Excited about going back to that hill, Katherine confidently walked to Lois’ house to get the sled.  When she got there, she got a big surprise.  

The sled was not there!  How could this be?  She had left it there, so of course it should still be there.  But it wasn’t.  What could have happened, she wondered.

She ran home.  “Mommy, my sled isn’t there!” she cried, her lower lip quivering.

“Oh, Katherine, that’s too bad.    I think someone might have stolen it.”

“What’s ‘stolen’?”

“Stolen is when someone takes something that doesn’t belong to them.”  

“But that’s my sled!”

“I know, but sometimes people take things they shouldn’t.  That’s why we have to take care of our things.  That’s why we have to put things away and not leave them outside.”

“But I want to do the sled again.”

“I know.  We’ll find something else you can use.  But let this be a lesson:  What do we need to do with our things?”

“Take care of them,” she sniffled.

“That’s right, Katherine."  She put out her arms. 

Come here, give Mommy a hug.”

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SCIENCE VOCABULARY

ENERGY        Energy is needed to do any kind of work. The sun gives us energy to grow our food. Then we get our energy from the food we eat.

We can pass this energy to a ball we kick, for example. In The Sled, our energy is used to help us pull the sled up hill. Then when we get to the top, we use our energy to push off and away.

FORCE     There are three kinds of forces:

Pulling

Pushing

Turning

In this story we learn about pulling and pushing forces. We cannot see the force, but we can feel and see what it does.

GRAVITY           Gravity is a pulling force that is in every single thing, no matter how big or how small. Small things have much less gravity; bigger things have much more gravity. Gravity pulls us down -- toward the ground. When we are going up a hill, gravity is pulling against us in the other direction.

This is why it is harder work to climb a hill. On the other hand, when we go down a hill, now gravity helps us go down. In fact, the farther we go down hill, gravity helps us to go faster and faster.

PULL         A pulling force comes straight back and toward you

PUSH       A pushing force goes straight ahead and away from you

WORK     Work is simply using energy and passing it along to something else or someone else.

For example, in The Sled, the work is:

Climbing the hill

Pulling the sled

Pushing off on the sled

ACTIVITY 1

You need: a toy car         a book

Open the book. Place it face down on a table or the floor. You have an uphill ramp and a downhill ramp.*

Place your toy car at the bottom of one side of the book. Will the car go up the book by itself? No, of course not, it needs your energy! Pick it up and roll it up the side of the book until it rests on the back of the book.

Now point it in a downward direction and let go. Did the car need a push from you? Not this time. Why? Gravity did the work and pulled it down for you.

ACTIVITY 2

You need: a wagon          a friend                a very low hill

Ask your friend to sit in the wagon   while you pull them up the hill. Then pull them down the hill. Which way was easier? Which was harder? Why?

Then ask your friend to pull you in the wagon.   Ask the same questions.

ACTIVITY 3

You need:     a bicycle

The next time you come to a hill when riding your bike, think about what you've just learned here!

*  Any ramp or hill is also called an inclined plane:
    -- An inclined plane is one of six simple machines.
    -- The others:  lever; wedge; screw; wheel and axle; rope and pulley
    -- Simple machines make it easier for us to do work.