Inertia

Peter Insley                   Retired
                           

Objective:

The idea is if enough demonstrations of inertia are done, the definition or 
meaning of inertia will become clear.

Here is a list of the things I did, what I used, and how I did them.

1.  Tablecloth and Dishes

Get heavy dishes from garage sales or resale stores.  Fill glasses 3/4 with 
water.  Use red dye to make "wine".

Use a cloth that has no hem on the side you are pulling under the dishes.  
Pull down, not back, on the cloth.  Try to have all dishes within 12 inches of 
the far edge of the table, and no dishes near your end.

2.  Eggs and Water Glasses

I used 3 eggs, 3 pieces of mailing tube (or paper towel tubes) cut down, a 
metal pie plate, 3 glasses of water, and a broom.

The trick is to hit the metal plate with the broom squarely (not up or down), 
and snap the plate out so that the eggs fall into the glasses of water.  The 
eggs need to be EXACTLY above the water.  Wide glasses help.

3.  Glasses and Blocks (Samuri Scientists)

Get 5 SMOOTH blocks stacked on top of each other, and put a glass of water on 
top.  Get something heavy to knock the bottom block out.

4.  Coin on Pool Balls

Lay a pool ball on a round filter paper, or somehow outline a circle around the 
ball.  Balance a quarter on the pool ball.  Hit the pool ball with another cue 
ball, and try to knock the quarter outside the circle.  You can cheat by making 
the target ball a little heavier that the cue ball.

5.  Ken and Barbie

Strap Barbie into a skate or small car, and leave Ken balanced on top.  Run 
them into a wall and watch Ken fly out.

6.  $20.00 Bill and Two Wine Bottles

Fill two wine bottles with water.  With one bottle standing upright, lay the 
bill across the neck opening, and then balance the other bottle upside down on 
top of the first bottle.  The idea is to pull the bill out without spilling any 
water.  Holding the bill tautly with one hand, use your other hand to hit the 
bill in a quick downward motion in order to pull it out.

7.  Hoop and Ring

Balance a hoop in the opening of a bottle, and then balance a piece of chalk on 
top of the hoop.  Get the chalk right over the neck of the bottle.  Then whip 
out the hoop and the chalk will drop into the bottle.

These activities have a lot of excitement and a pretty high failure rate.  It's 
a good idea to let a student try to do the activity after you do it, to show 
them how it is done.  A failure is almost as much fun as a success.

The general conclusion from our class was:

All heavy objects seem to have a "lag time" before they get moving (or in the 
case of Ken, before they stop).  The heavier the object is, the greater the lag 
time.  This is inertia.

Then John said:

"An object at rest will stay at rest, and an object in motion will stay in 
motion in a straight line unless an unbalanced force acts on it."

We decided John was unbalanced and we went back to our original conclusion.