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Description (overall plan) The goal of this project is to measure the velocity of a
cork shot from a bottle full of combusting ethanol vapors. We
began building this experiment by inserting 2 screws in opposite
sides of a bottle. We poured a little bit of ethanol into the
bottle, corked the bottle, and shook it, to create vapors.
These vapors were then ignited by a spark that jumped across the
screws, which was created by a charcoal grill starter. List of Equipment
Description of Equipment On a table we have a ring stand with a photogate attached to it standing next to a bottle. The photogate is placed to hang above the 250 milliliter bottle and is attached to a sensitivity adjuster. This adjuster is connected to a delay unit, whose delay output is connected to a second delay unit. The second delay unit’s outputs are connected to two Vivitar 283 flash units, which are attached to the ceiling above the experiment. The bottle has two screws, which are connected to wires with alligator clips, and the other ends of the clips are connected to a charcoal grill starter. A meter stick is attached to a different ring stand, which is beside the bottle. A camera is located about 1.2 meters away from the bottle. On the camera we are using a 28 mm lens in order to have both shots of the cork, from the double exposure, in the picture. When we use the MotionScope 800s we remove the flash units, delay units, photogate with sensitivity adjuster, and the ring stand. We also put the MotionScope in the place of the camera and the cart with the viewing screen of the MotionScope is placed to the right of its position relative to the front view of the setup. Also, the lights have to be left on for the MotionScope to be able to capture the video.
This is a front view of our setup.
This is a top view of our setup. Description of Triggering, timing, and imaging methods A photogate is placed directly above the cork and is connected to a photogate detection circuit, which is connected to a delay unit. Another delay unit is plugged into that delay unit's delay output. The second delay has both the flashes plugged into its outputs.
When the photogate is triggered the output of both flashes are delayed. Flash one is delayed by the first delay unit. Flash two is delayed by both units, so after the photogate is triggered there is an extremely short delay then the first flash goes off. Then, there is another extremely short delay, and then the second flash goes off. This way if the camera shutter is open during the entire event a double exposure is obtained and the cork will appear twice in the picture enabling us to calculate its velocity. In order to obtain a picture we open the shutter for two seconds, set off the spark with the grill starter, the spark ignites the ethanol vapor, the cork shoots off, triggers the photogate, the first flash goes off, the second flash goes off, and then the shutter closes. When we used the MotionScope 800s we removed all the time delay units, flashes, and the photogate, along with its components. To obtain video, one of us hits the record button and the other one immediately triggers the explosion. After the explosion is complete and the cork is out of the frame we then hit the stop button to stop recording. We review the clips on the MotionScope viewing screen and, if we like it, we record it onto a standard video camera. These recordings can now be uploaded to a computer and used for analysis. In Depth Description First of all, if you have ceiling tiles, the ceiling tile above the bottle must be replaced with a sheet of Plexiglas to prevent the tile from being damaged. Use a 250 milliliter polyethylene bottle with two nails or screws through the sides. Pour a small amount of ethanol (0.8 milliliters) into the container. The top of the bottle should be sealed with a cork or rubber stopper. Shake it up to ensure that the liquid ethanol has come to equilibrium with its vapor. The nails should be connected to a charcoal grill starter with alligator clips. Press the button on the starter and the resulting spark across the screws ignites the ethanol vapor and blows the stopper off. Make sure to have a meter stick beside the bottle so displacement can measured. |
