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.”

                               ########################

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.

GATEWAY TO SCIENCE: Sports and Games, Episode 1

                                              MY NEW TV SHOW!    

THESE ARE THE TIMES YOU CAN VIEW IT ON QATV, CHANNEL 8:
Fri., Feb. 14, 6:30 p.m.  --  Sat., Feb. 15, 8:30 p.m.  --  
Sun., Feb. 16, 12 noon  --   Mon., Feb. 17, 4:00 p.m.
Fri., Feb. 21, 8:00 p.m.  --  Sun., Feb. 23,  6:00 p.m.

Well, I've just done episode 1 of Gateway to Science:  Sports and Games.  It was done with the help and facilities of Quincy Access TV.  Glad to have finally gotten it started!  Frank was my co-host.  After a conversation about some background of the show, we later showed two videos put on by the National Science Foundation (Science360.gov) and NBC (NBCLearn.com).  

The first video was "Figuring Out Figure Skating."  Before showing it, we reviewed two of its science points.  The first was about how a figure skater speeds up and slows down while spinning.  She gains speed by pulling in her arms, close to her center of axis and reducing drag.  She slows down by extending her arms, away from her center of axis, increasing drag.

 

The second science point concerns angular momentum.  Normally when you think of momentum, it's about motion going in a straight line, also called linear momentum.  However, it is different when something is turning.  When the force you apply to someone or something is a turning force, we call this torque.  Torque generates angular momentum.  Why is it called angular momentum?  Think of a circle.  A circle has 360 degrees, full of angles as you go all around the circle.  This is why we say a rotating or turning object has angular momentum.

Using a swivel chair from the studio, we tried to illustrate how a figure skater speeds up and slows down.  However, the initial spin wasn't too strong.  The extending and pulling in of the arms of the volunteer -- Frank -- did not illustrate this point as dramatically as we hoped it would.  We didn't want to try it again for fear of his getting dizzy!  (I got dizzy doing a practice spin!)

After showing the video, I read off a list of other videos that I recommend watching for different reasons.  They are:

AIR LIFT:  SKI JUMP     About generating lift.  Beautiful to look at.

BLADE RUNNERS:  SHORT TRACK SPEED SKATING   3 laws of motion

DOWNHILL ALPINE SKIING     Focuses on the 2nd law of motion.
                                            Speeding forces and slowing forces.

SAFETY GEAR                        Good explanation of elastic collision.

BOBSLEDS, BANKING ON SPEED   Pulls many physics terms together; 
                                                  brings in some history with Galileo.

SHAUN WHITE AND ENGINEERING THE HALF PIPE     Well illustrated.
Attention skateboarders!  Relates design and engineering.

SCIENCE OF SKIS - SCIENCE OF SKATES - COMPETITION SUITS
These videos get into materials science and engineering.

MATHLETES      Arithmetic, algebra, calculus applications.  Geometry, too:  great illustration of the angle of access at the hockey net.




After this, in preparing to show "Aerial Skiing, Ski Jump," I presented a preview of the video.  Aerial ski jumpers employ three different types of twisting:
1, The WHOLE BODY is involved with contact twisting. When you apply torque to a mass, the rotating mass has angular momentum.
2, The ARMS use tilt twisting, precise arm movements that regulate spin, speed and orientation.
3, The LEGS move in a way similar to that used in hula hooping.

Hula hooping was then nicely demonstrated for us by Mark Crosby of QATV who, happily, did not require too much cajoling to be pulled in as a volunteer.  He did quite well.

After the video was over, we segued from the Winter Olympic sports to the popular winter sport of sledding.  I read the first few pages of a book I wrote, "The Sled:  A Matter of Some Gravity."  I wrote it a year ago when I had a chance to work with some of the children at Head Start, Quincy.  Being there with the children spurred me on to write a story for them in which a little science is added to a child's play.  I only had time to read a few pages, but at the next show I'll read the rest of the story.  I hope anyone with young kids will encourage them to watch.

I showed an assortment of some of the things I've been collecting over the years, including sport science books, games such as jump ropes, toys such as balloons and frisbees, etc.  They'll be used in future shows.