Inertia: The Non-Rolling Marble

To prepare:

Glue a thin washer onto a piece of paper.

Set a marble in the washer.  Quickly pull the paper out. 

If you move quickly enough, the marble will remain where it was.

Inertia: Catch a Quarter

Place your hand by your ear and raise your elbow so your forearm is parallel with the floor.

Place a quarter on your elbow.

Quickly move your elbow down and attempt to catch the quarter in the same movement. 

Due to inertia, the quarter wants to remain in the same place, rather than move with your arm.  If you move quickly enough, you can catch the quarter before gravity pulls it out of your reach.

Inertia: Penny Passengers

Place a penny on top of a small toy car.

Roll the car so it runs into a thin book or piece of corrugated cardboard.

Observe the car and the penny.  What can you learn from this activity about the importance of seat belts?

What difference does a seat belt make?  Try again, using a small piece of tape to hold the penny on the car.   

Do different coins respond differently?  Dimes are lighter than pennies, quarters are heavier.

Note:
You need to push the car very gently, or you'll observe a different form of inertia - the car will move out from underneath the penny and the penny will drop to the table. 

Inertia: Penny In a Cup

If you found getting a penny to balance on your finger to be a bit too challenging, this might be more your speed. 

Place an index card on top of an empty cup.  Set a penny in the middle of the index card.

Flick the card out....

...and the penny falls into the cup (the cup is a much larger target than your finger!)

Inertia: : A Penny for Your Finger

Hold out the index finger on your non-dominant hand.  Balance an index card on your finger and then place a penny on top of the card (so that the penny is essentially sitting on your finger - there's just an index card between them).

Use your dominant hand to flick the index card out of the way.  If things are balanced properly and you flick the card quickly enough so that inertia overcomes friction, you'll be left with a penny balanced on your finger. 



Inertia: The Tale of Two Cups

Here's the set-up:
You have two identical-looking cups, each sitting on an identical pieces of paper. 

You apply Newton's first law or motion (an object at rest will stay at rest, an object in motion will stay in motion, unless acted on by an outside force) to remove the pieces of paper, leaving the cups in the same location.

But...

...when you go to do it, one stays nicely in place while the paper is pulled out from under it.  The other cup doesn't cooperate so nicely.  It slides around with the paper.  In fact, it almost seems impossible to remove the paper from under the cup without lifting up the cup.

Why?  What happened to Sir Isaac Newton's law?

Inside one of the cups, you've placed a weight (anything massive will do - marbles, pennies, etc.).  Objects with more mass have more inertia - they're more resistant to changes in motion.  So, the cup with the weight in it has more mass, therefore it has more inertia and is more resistant to moving with the paper (i.e. it has an easier time staying where it is when the paper is removed). 

The styrofoam cup with nothing inside of it has very little mass and therefore very little inertia.  As a result, it is very difficult to remove the paper from underneath the cup. 

Inertia: Sugar Cubes in a Flask

This is a fun inertia activity for your students to try. 

The set-up:

A flask (or bottle) set on the table.

The inner ring from an embroidery hoop* balanced on the opening of the flask.

Sugar cubes, in a stack, on the hoop, so they are directly over the opening of the flask. 

The objective:

Knock the ring out of the way, so the sugar cubes fall directly into the flask. 

Some of your students will really get the hang of this and be able to get a sizable stack of sugar cubes to fall into the flask. 

You can also stand a dry erase marker on top of the hoop and try to get it to fall in. 

*Embroidery hoops can be found in craft stores (AC Moore, Michael's, JoAnn Fabrics, etc.).  They consist of an inner ring, which is a perfect circle, and an outer ring, which has a screw closure to tighten it.  Most of them are made of wood.  You can sometimes find plastic ones or if you're at a thrift store/yard sale you might find some metal ones.  For this activity, you can only use the inner ring.  I haven't found anything that requires only the outer ring yet - still looking! 

Inertia: Knock the Penny Out

Make a stack of 5 or 6 pennies. Use another penny to try to knock the bottom penny out, while keeping the rest of the stack in tact.

Go a step farther and make your stack of pennies on a piece of paper. Trace a circle around the pennies. Now, try to keep the stack of pennies in the circle after you knock the bottome one out.