Motion is the change in position over time. Students often have a difficult time understanding that concept graphically, which is one of the big 8th grade science standards. Vernier's Go!Motion sensor and software are excellent demonstration tools. The video demonstrates how both of them work together. Usually when I introduce it, I just give a volunteer student a big (1 x 1 yard) whiteboard and tell the student to walk towards and away from the sensor. The students can see the graph on the large video screen. They quickly pick up that the farther away from the sensor the student is, the higher on the graph the line is and vice versa. I have them draw graphs what what they think certain types of motion are and then we see if we can replicate the graph. The software also allows a prediction graph to be drawn and then students can see if they can walk that same motion graph. In later lessons, acceleration graphs are explored. Having a class set would be ideal, but having one sensor with a computer hooked up to a video projector will work just fine.
The densities of different liquids can be easily demonstrated by making a density column. Steve Spangler has a splendid density column demo that I decided to make on a much larger scale. Instead of using a graduated cylinder I decided to use a fluorescent light bulb tube guard. To seal one end of the tube I used duct tape and Goop so that no liquid would leak out. Once the tube is ready, it's just a a simple matter of pouring the liquids into the tube according to their densities. Check out the video for the results and for some additional tips.
A dollar bill is soaked in 2 parts water, 2 part isopropyl alcohol, and then lit. The liquid burns off, but the dollar bill doesn't ignite. Watch the video for an explanation.
I picked up this in a toy shop. Students are fascinated by it and always wonder how it works. Once they learn about density, they figure it out pretty easily.
Eggs have an arch design in which compression forces are diverted from the top and bottom of the egg down to the sides. How much compression force can an egg take before it's smashed? Watch the video!