Modeling Projectile Motion Lab
This straight-forward physics lab activity has students constructing an accurate model of an object’s flight path as it is pulled down by gravity. This is a relatively simple lab to construct and the students can get a hands-on understanding of the physics behind falling objects. This lab also allows the students to predict and model how far an object will fall 7 seconds into the future! A rubric and short answer questions follow the model construction.
This lab activity will have students measuring out various lengths of string, which represents the distance a falling object will travel in a given amount of time. They will then attach this string to a popsicle stick shaft, which represents the straight-line path a projectile would take if there were no gravity. I typically have the students make the straight-line stick out of multiple popsicle sticks hot-glued together. To keep the lengths of the strings hanging downward, the students tie nuts or washers to them. After the students complete 7 of the string lengths, they will then have to use the distance formula (D = .5 gt2) to figure out the appropriate distances. There is a rubric followed by 4 short answer questions.
The total time for this lab activity is one full class, roughly about 50-55 minutes. The lab is three pages in length.
Materials needed for the lab:
• Popsicle sticks. I buy these off Amazon. The best I have found is by Pepperell Crafts, “Natural Wood Craft Sticks.” These come in a pack of 1,000 for about $13. They are slightly more expensive, by a few dollars, than some of the competitors, but they are much straighter and less warped than anything else I have come across.
• Mini hot glue guns. I have picked these up over the years at various craft stores. I have found that quality is fairly consistent, so shop where you can get the best price.
• Mini hot glue sticks. I also buy these in bulk off Amazon. Quality is similar among different brands, so just buy according to price.
• Nuts or washers. Buy these at any local hardware or big-box store. I prefer nuts—they have more mass and hang better.
• String. The string that hangs the best would be the Natural Cooking Twine, available from Amazon. This is the kind of string you use for trying up chickens or turkeys. The only problem with this twine is that it tends to fray along the edges, frustrating students. But it is great for trying knots. The only better string is available through science supply stores, like Flinn. The kind of string they sell does not fray as bad. Synthetic string from big-box hardware stores looks cool, but it does not hang well. I would avoid this type.
• Meter sticks. Use these to make off the lengths for hanging the strings on the popsicle sticks. Also use to measure the length of the individual strings.
• Scissors. To cut the string.
Calculators: To compute distance.
• Wire cutters (optional). These are used to trim the popsicle sticks, if needed. These can be purchased at your local hardware or big-box store.
1. Have the students glue the popsicle strings together so that the total length is 45 centimeters long. Pick off the extra hot glue as needed to improve appearance.
2. Every 5 centimeters, place a small mark on the popsicle stick rod you just created. These will be where you hang the strings from. Start making at the 5 cm mark, 10, 15, and so on until you get up to 45 centimeters (which should be at the end of the popsicle sticks.)
3. Now cut the strings to the appropriate lengths. When cutting the strings, make sure the students give themselves a few extra inches so that they can tie the knot easier. The students will have to calculate the lengths for the strings. There is a place on the worksheet for them to do this. Note: To make the numbers more workable, use 2 m/s2 for the acceleration due to gravity. Earth’s gravity of 9.81 gives us numbers that are too big to effectively use for this demo.
4. Attach the strings to the marks on the popsicle stick rod. At the other end of the rod, the longest piece of string should hang.
Remind the students to be accurate in their measurements!
5. Trim off any loose pieces of string. Make sure their names are on their final products.
Tips and Hints for the Lab:
• The biggest issue with this lab is safety. You can simply tie the string to the washers and sticks if you want. But hot glue gives a more polished look to the lab. If you are using hot glue for the lab, make sure the students have been informed on proper safety steps to use while working with hot glue. For some, this is the first time they will be working with hot glue. For others, they will be seasoned pros. The most common accidents I have while working with hot glue is that students will put down the hot glue gun and accidently rest their hand on it. To try and prevent this, I constantly remind them to place hot glue guns in the center of the lab table while not in use. Burns are typically not severe, but they can cause blistering, if the exposure is long enough. Have some ice on stand-by just in case. BURNS WILL EVENTUALLY HAPPEN. Be prepared. Conceptual Science Lessons cannot be held liable for student injuries. Proceed at your own risk.
• Needless to say, use safety glasses/goggles.
• When collecting the final products, it may be helpful to have them put it into a plastic baggie, otherwise the strings from different projects tend to get all tied together.
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