Name of Activity Mountain Rescue STOMP car, climb, incline, gears, gear ratios, NXT NXTs 4, 5, 6, 7, 8, 9+ 1 Hour Total Students will build or modify a car to climb a steep incline using gears. – To learn about gears and gear ratios. – To learn about forces involved with inclines and gears. – One NXT car per group. – An assortment of different sized gears. – Steep incline. Construct a steep incline that is wide enough for an NXT car to climb. Arrange students into groups of two. Photocopy enough worksheets for the class. Distribute necessary materials. Gears can be used to increase or decrease power in a machine; for example, a can opener. Gears are used in many modern inventions and everyday devices. Gears can also be used to change rotational motion. Gears ratios are used to compare gears of different sizes. The size of a gear is measure by the number of teeth or cogs that are on the outside of the gear. The formula for a gear ratio is: (number of teeth on gear #1)/(number of teeth on gear #2). Gear ratios can be used to detrmine how many turns of the second gear their will be for the number of turns of the first gear. The gear that is mechanically turned by a person or a motor is called the drive gear. The gears that turn as a result of the drive gear being turned are called the followers. gears turn in opposite direction of the gears directly next to them. A car driving up an incline has more forces acting against it than a car driving on a flat surface. Gravity has a different affect on a car driving up a ramp and pulls the car down the slope. As a result, a car driving up a ramp requires more power. Friction is also an important factor for a car driving up a ramp. The more friction the better grip a car will have on the surface of the ramp and the less likely the car will be to slide back down the ramp. Vocabulary: gears gear ratios drive gear follower gear gravity friction slope Discuss gears and gear ratios with students. Have students fill out worksheets on gears and gear ratios. Discuss the forces acting on a car driving up a ramp. Discuss the difference between a car that drives on flat ground and a car that drives up a ramp. Have student build an NXT car or provide a pre-built NXT car. These first cars should not have gears attached. Have student program their cars to drive for about 20 seconds (enough time to climb the ramp) at a power of about 75 (a power too great for the car to climb the ramp without falling off). Allow students to try to drive their car up the ramp. Come together as a class and discuss why the cars had difficulty climbing the ramps. Tell students that they are not allowed to reprogram their cars, but must use gears to give their cars enough power to climb the ramp. Have students add gears to their cars and test the design on the slope, let them try different gear ratios and combinations. Students can attach a proximity sensor to their car to prevent the car from falling off the edge of the ramp. http://sites.tufts.edu/stompactivitydatabase/files/formidable/63_image_2.jpg http://sites.tufts.edu/stompactivitydatabase/files/formidable/63_image_3.jpg http://sites.tufts.edu/stompactivitydatabase/files/formidable/Gear_Ratio_Worksheet.pdf http://sites.tufts.edu/stompactivitydatabase/files/formidable/Gears_Worksheet.pdf http://sites.tufts.edu/stompactivitydatabase/files/formidable/mountain_rescue.doc
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