Inertia: the Egg Drop
The above version requires Quicktime 7
To play a smaller version of the video, left-click here; to download the video, right-click here (PC) and "save link as" or control-click (Mac) and "save target as"
The Big Idea
An object in motion will stay in motion in a straight line unless acted on by an outside force. An object dropped from a moving vehicle will fall in an arc, continuing to move forward as it falls.
Details
All matter has the tendency to continue doing what it is already doing - moving if it is moving, and staying at rest if it is at rest - unless it is acted on by an outside force. This property is an object's inertia, which comes from the Latin for "laziness." In this demonstration, as the chicken drops the egg, it continues forward even as it falls. You can see that the egg follows directly under the chicken's hand in the following stills:
|
|
|
|
Notice that relative to the car, the egg is falling straight down. Relative to the pan, however, the egg is falling in an arc, since it continues moving forward even as it is acted on by gravity. It only stops moving forward when it is acted on by the force of friction with the ground. Since the above images are framed around the car, it may be hard to imagine the "pan's" perspective. Take a look at the stills framed differently:
 |
 |
 |
 |
This is similar to a child tossing a ball up to himself while riding in a train. Relative to the child and the train, the ball is going straight up and down. Relative to an observer on the train platform, the ball is going up and down in forward arcs. The concept of relative motion allows us to understand how we see things around us as being stationary even as we are all hurtling through space at tremendous speeds; it also help explain why the sun seems to be moving overhead during the day, while in fact, the effect is the result of us spinning on our axis.
Materials and Set-up
This experiment is fun to do with a car, egg and frying pan, as it was done in the video, but it is just as effective in the classroom with a set of keys. Have a student run by an sheet of paper holding a set of keys at their waist. Their goal is to let go of the keys (just let go, not throw) in order to have them hit the paper. They will soon find that they need to let go before they get to the paper. Other students will see that the keys are falling in an arc; to the student running, the keys are falling straight down. The faster the student is running, the sooner he or she must let go in order to hit the target.
Safety Issues
If you choose to do this demonstration from a car, be sure to wear seatbelts and pay attention to other things that may be going on in the parking lot where you are laying your eggs.