“For the LAST TIME, I told you to stop unbuckling your seatbelt!”

Yes, parents, I know all too well the anxiety of looking in the rearview mirror while careening down the highway only to see that your smiling child has undone their seatbelt yet again.  And you wish you could send your Go-Go-Gadget retractable arm back there to secure them, but you can’t… because 1) that sadly doesn’t exist, and 2) you are in charge of making sure your car doesn’t crash into that truck in front of you.  ARGH! If only your small child could understand the DANGERS of unbuckling their seatbelt!

So let’s put that bin of Hot Wheels cars to some good use and experiment with INERTIA!

**NOTE**   This activity is divided into 2 posts. Part I is the initial set-up of the activity and explanation of INERTIA. If you have toddlers or children who can’t yet write, Part I is probably all you will want to do.  Parents of older children with writing and number skills should also check out Part II – Test a Hypothesis.

LEARN SCIENCE VOCABULARY:

Inertia – the tendency of an object to keep doing what it was already doing. (You may remember this from school as “An object in motion tends to stay in motion, and an object at rest tends to stay at rest, unless acted on by an outside force.”  Also known as Newton’s First Law of Motion if you want to be Smartypants.)

Collision – When 2 or more objects crash into each other.

MATERIALS NEEDED:

• Hot Wheels car (They usually sell for $1 at any grocery store.)
• Play-Doh (It helps if it is relatively fresh, so it will be more sticky.)
• Stack of books (or a box)
• Tape (Masking tape works best)
• Pencil (a pen, marker, or good ole stick will also work)
• Hot Wheels ramp or track (if you don’t have this, just make one out of cardboard!)
• Ruler or measuring tape

HOW TO RUN THE EXPERIMENT:

1. Use your stack of books (or box) to prop up your ramp at whatever height you choose.  Tape the ramp in place.
2. Measure 10 inches from the bottom of the ramp and tape down your pencil.  This is the “brick wall” that makes the COLLISION in the experiment.  (Here is a great opportunity to practice counting with younger toddlers or reading numbers and using a ruler with the older kids!)

   

3. With the Play-Doh build a small “man”, about 1/2 inch tall, to be your crash test dummy.  He does not have to be extravagant or anatomically correct.  I usually build more of a “blob.”  Give him a name.  (We’ll call ours “Mo.”)
4. Stick Mo onto the hood of the Hot Wheels car.  He should be stuck well enough so that he doesn’t just tip off, but not so stuck that he becomes a permanent fixture on the car.

   

5. Ask your child to make a guess as to what will happen to Mo when the car has a COLLISION with the pencil.  (This is their hypothesis. For more on making and testing hypotheses, check out Part II of this activity!)
6. It is time to run the experiment!  Hold the car with Mo on the hood at the top of the ramp and let it go.  You should expect the car to hit the pencil and stop, but Mo continues to move forward off the hood of car and lands some distance in front of the pencil – Mo has INERTIA!  (As with all experiments conducted outside of a highly precise lab environment, it won’t work perfectly every time.  But that’s ok – that’s why we call it “experimentation!”)

   

7. Send Mo down the ramp as many times as your child wants.  Decide if their guess was correct or not. Kids may want to change the experiment by raising or lowering the ramp, making Mo bigger or smaller, putting the pencil further away, etc.  This is great scientific thinking! (See Part II for more info on making and testing each new hypothesis.)
8. Now let’s give Mo a “seatbelt” and see if that changes his destiny! (Have the kids make a guess…will he be safe this time?)  Use the tape to strap Mo down to the hood of the car, and send him down the ramp again.  (This time he should stay put on the hood of the car.  If not, your seatbelt is faulty!)

   

THE SCIENCE BEHIND IT:

Mo, of course, is demonstrating what could happen in a car crash if someone is not wearing their seatbelt.  His body has inertia, meaning that even though the car stopped (or possibly even reversed) when it hit the pencil, there was nothing to stop Mo’s body from continuing to move forward. When we gave Mo a tape seatbelt, the seatbelt provided the force to stop the inertia of Mo’s body.

Inertia can be felt anytime you slam on the brakes in the car and everyone feels like they are jerked forward.  You are actually not being “pushed” forward when this happens… but rather your body, which was moving forward just as quickly as the car you are riding in, continues that forward motion until the seatbelt stops you.

CHECK OUT HOT WHEELS CRASH TEST DUMMY PART II – TEST A HYPOTHESIS TO TAKE THIS EXPERIMENT TO THE NEXT LEVEL!!  (FOR OLDER KIDS WITH WRITING SKILLS)