Sci-Fri: Inertia

Our science lesson today in BFSU was Newton’s First Law of Motion, namely: Inertia!

In physics, Inertia is the law that, simply put, states: “an object in motion tends to stay in motion, while an object at rest tend to stay at rest.” My objective was to expand on our earlier lessons on matter and energy and help relate these concepts to real life.

The Lesson:

We started off with two activities that the kids could have some fun with. The first was the old tablecloth trick, except that I don’t have a tablecloth so we did it with a glass of water and a piece of paper. This trick demonstrates the first part of the law of inertia, “an object at rest will stay at rest unless an outside force acts on it.” When the paper is yanked out from underneath the glass there is not enough force to break the inertia of the glass so it stays put. We also observed that if you move the paper more slowly the glass will move with it, but of course this is due to friction between the paper and the glass. We discussed the idea that every day objects don’t go zooming around unless someone or something has acted on them. If a toy is left on the floor, we can expect it to still be there an hour later unless little brother has moved it. This part of inertia is fairly easy to understand so we moved on quickly.

Our next activity was a game involving a bean bag held at shoulder height and a target bowl placed on the floor. The kids had to run past the target and drop the bean bag at just the right time, without stopping, so that it falls into the bowl. The trick is that the bean bag continues to move forward after it is dropped so that it must be dropped early to hit the target. To better illustrate, I had the boys stand next to the bowl while I did the activity. From that angle they were able to observe that when I dropped the bean bag it moved diagonally rather than straight down.

We discussed how this game illustrates the second part of Newton’s First law “an object in motion will continue moving in the same direction and at the same speed, unless another force acts on it.” Of course on Earth objects do not continue moving indefinitely because we also have gravity and friction to take into account. I like to start by thinking about how objects in space behave to better illustrate what it really means to “keep moving in the same direction at the same speed.” If we could toss a tennis ball in open space we could clearly see this principle. Unless the tennis ball encounters a gravitational field or another object it will move forever through space in the same direction. Astronauts who perform maintenance outside the International Space Station wear a tether line for just this reason. Objects behave differently on Earth primarily because of gravity and friction. We talked about every day ideas such as why we trip forward instead of sometimes tripping backwards and why seat belts are required in the car.

The boys had fun with these ideas, attempting to trip backwards and finding that they could only do so by either walking backwards or changing their center of gravity as they fell forward. Somehow our discussion of cars ended up with us yanking chairs out from under each other.


After finishing up our discussion I thought it would be fun to give EJ some free reign to choose an experiment for him to perform to demonstrate the concept of inertia. I helped him do a search for inertia experiments on YouTube and told him to pick one that he knew we had the materials for, to set it up and call me when it was ready to go. First, he tried to pick a vacuum experiment involving a candle which of course is interesting but has little to do with inertia. Finally he chose the Egg Drop. It worked perfectly as you can see in our video.

As always, thanks for reading!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s