Activity No. The Physics of Hula-Hoops

Transcription

1 Activity No. The Physics of Hula-Hoops Objective: In this activity you'll get to create your own Hula-Hoops and investigate how their weights affect how they spin. Which do you think will spin better, a heavy hoop or a lighter one? Background: What makes a Hula-Hoop spin around a person's waist? It comes down to a combination of several forces at work. When the person inside of the hoop moves their body to propel the hoop around them, they're exerting an upward force (from their hips) and a turning force known as torque. Torque is a twisting, outward force that is needed to cause the hoop to spin. (More technically, torque is required to keep the hoop spinning because it's needed to keep the centripetal force going.) Another force involved in the Hula-Hooping process is friction. For example, if a ball is rolling along a flat surface, it eventually stops due to the friction created by its contact with the surface. Friction between the hoop and the hula-hooper's clothes and the air will slow the hoop's spin down. Friction, however, also helps to keep the Hula-Hoop up on the hooper's body while the force of the Hula-Hoop's weight pulls it down. (This downward force is due to gravity.) How do you think the hoop's weight affects how it spins? Hypothesis: Materials: Hula-Hoop of various sizes and weights, sand, duct tape, cutter, cup, triple beam balance Procedure: Part A:

2 Now you will do some hula-hooping with your homemade Hula-Hoops. If you need directions or tips on how to hula-hoop, you can watch an instructional video online, such as this one. Pick up the lighter two Hula-Hoops to try first. Have one person (yourself or a helper) hula-hoop with it around their waist while a helper starts timing the hula-hooper as soon as they reach a steady pace. Have the helper time the person for one minute and count how many full turns the hoop makes during that time. If the hooper cannot hoop through the full minute with the Hula- Hoop, try starting over again or try collecting data for only 0 seconds. How many times could the hula-hooper spin the lighter hoop in a minute? How well could the hooper spin it around? Does it seem awkward or does it spin well? Repeat this process with the heavier Hula-Hoop, again timing how many spins the hula-hooper can do in one minute. (Make sure the hooper doesn't change clothes while collecting data.) Did the hula-hooper spin the heavier hoop faster or slower than the lighter one? Why do you think this is? Did this hoop feel more or less awkward to spin, or about the same as the other hoop? Which Hula-Hoop spun faster, the lighter or heavier one? Was the faster Hula-Hoop also the one that was the easiest to spin, once it got going? If you want, you can repeat this process a few more times for each Hula-Hoop. Are your results consistent? For even more data, the hula-hooper and helper can switch roles and repeat this process for both Hula-Hoops. Did the other person get similar results? Part B: In this activity you compared Hula-Hoops that were the same size but had different weights. How does the size of the Hula-Hoop affect how it spins? Part C: You could make a broader range of Hula-Hoops, such as by adding different amounts of sand and/or making several different sizes. Is there a relationship between speed, the weight and/or size of the Hula-Hoop? If so, what is it? Part D: Try hula-hooping in different types of clothes. Do different garments affect the speed at which the Hula-Hoop rotates? Can you correlate your results to the force of friction?

3 Observations and Results: Part A: Using Different Sizes of Hula-Hoop Table A: Bigger Hula-Hoop (student A) Table A: Bigger Hula-Hoop (student B) Table A: Smaller Hula-Hoop (student A) Table A: Smaller Hula-Hoop (student B) Part B: Using the Same Diameter Hula-Hoops

4 Table B: Same diameter Hula-Hoops lighter (student A) Table B: Same diameter Hula-Hoops lighter (student B) Table B: Same diameter Hula-Hoops heavier (student A) Table B: Same diameter Hula-Hoops heavier (student B) Part D: Using Heavier Hula-Hoops with Bulky Clothes On Table D: Heavier Hula-Hoop with Bulky Clothes On (student A)

5 Table D: Heavier Hula-Hoop with Bulky Clothes On (student B) Table D: Lighter Hula-Hoop with Bulky Clothes On (student A) Table D: Lighter Hula-Hoop with Bulky Clothes On (student B) Analysis: Did the heavier Hula-Hoop spin slower than the lighter one? Was it harder to spin the heavier Hula-Hoop for a long time than it was to spin the lighter one?

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