Acceleration is the change in velocity over time. Velocity changes when speed, direction, or both changes. Anyone can build a simple accelerometer. The video below shows how to build an accelerometer and how to use it.
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Teaching how the eyeball works usually involves showing diagrams of the eyeball and showing how light passes through the lens. Science teachers can also use Jello to make lenses that will show laser light refraction. I tried that and had disastrous results. I started to play around with mixing baby powder (mostly cornstarch) with red food coloring and water. I was quite pleased with the results. Go ahead and watch the video below to see what happens.
The idea for this demo came from Steve Spangler Science. In his post he states:
Tonic water might not be your first choice for a beverage, but it's the secret ingredient you'll need to make a glowing geyser. It turns out that tonic water will glow under a black light because tonic water contains quinine, a chemical that was originally added to tonic water to help fight off malaria in places like India and Africa. While the tonic water we drink today only contains a small amount of quinine, it's still enough to make your drink glow under black light.
Instead of using mentos to make a glowing gyser, I decided to do a Hero's fountain version. You can get a simple apparatus from teachersource.com that fits into 2 2L bottles. Where in your curriculum can you fit this? In eighth grade science we cover properites of matter such as denisty, phase at room temperature, color, flame color, smell, texture, etc. Some chemicals can be identified from the ability to fluoresce when exposed to uv light. I would maybe do this with a fountain of regular water and one with tonic water and then ask the students if the same chemical is in each founatin.
The alkali metals are highly reactive since they have one valence electron. One of those metals is sodium. It needs to give up one electron to become stable. When a cubic centimeter sized piece of sodium is placed into water, a vigorous chemical reaction occurs in which sodium hydroxide (NaOH) and hydrogen gas is produced. Wikipedia provides an excellent description of what happens during the reaction.
Sodium reacts exothermically with water: small pea-sized pieces will swim around the surface of the water until they are consumed by it, whereas large pieces will explode. While sodium metal reacts with water, you can observe that the sodium piece melts with the heat of the reaction to form a perfect sphere shape if the reacting sodium is small enough. The reaction with water produces very caustic sodium hydroxide and highly flammable hydrogen gas. In any case these are considered an extreme hazard and will cause severe skin and eye injury.
In the video below a small pea sized piece of sodium is placed into water. It does ignite and explode. To avoid an explosion ice water should be used. To avoid ignition a safer method can be used in which a layer of mineral oil is placed on top of the water. The mineral doesn’t react with the sodium and prevents ignition.
For a safer sodium demo, fill a large graduated cylinder with and equal portion of water and mineral oil. The mineral oil will be on top. When sodium metal is dropped into the cylinder it won’t react with the mineral oil and when it touches the surface of the water, it reacts briefly to produce hydrogen gas bubbles, thus causing it to rise back up into the mineral oil.
When chemicals burn, it is really a chemical reaction between the substance and the oxygen in the air. When substances do not get enough oxygen, they don’t burn completely. Below is a video of 30 ml of flour exposed to a flame. Only a small fraction of the flour burns, while the rest does not. The surface area of the flour is quite small and needs to be spread out.
If the flour particles spread farther out from each other, more oxygen will be able to react with them. The following demo does just that.
The three pictures below show the required materials.
Place the pie tin with candles on a chair so that the pie tin sticks out a few feet. The meter stick can be kept in place by placing a few books on it. Measure out about 50 ml of flour and place into the sifter. Stand on a chair and sift the flour so that it falls onto the candles. Caution: Wear goggles, lab coat (or apron), and keep flammable materials away. Have a fire extinguisher close by just in case. Do not use too much flour!