Brief Description:

Students will use gear ratios to design cars that can complete a flat course and an inclined course.

Time: 1 hour

Keywords: gears, gear ratios, NXT robotics, cars, torque, speed

Lesson Objectives

• Students will use their knowledge of gears to determine whether “gearing up” or “gearing down” is better for each course

Materials

• NXT robotics kits or Simple Machines kits
• Cardboard inclined plane

Procedure

1. Review gear ratios. Define gearing up and gearing down.
1. Gearing up means that for every revolution of the drive gear the follower gear turns more than one revolution. This is useful when you want to make something move faster and give less power to whatever is attached to the follower gear.
2. Gearing down means that for every revolution of the drive gear, the follower gear turns less than one revolution. This is useful for when you want to give more power to whatever is attached to the follower gear but it moves slower.
3. If the drive gear is bigger than the driven gear, the car will be geared for speed. If the other way around, it will be geared for torque.
2. Introduce the challenge.  Students will have to design two different cars, each one specialized to move as fast as possible in a race course.
1. Course 1 is a just a flat course.
2. Course 2, however, is an incline.
3. A car geared for torque will be slower, but will climb better. A car geared for speed will be quick, but might not be able to climb the ramp.
3. Allow students to design their cars, discussing which gear ratio is best for each course.
4. Allow students to build, test, and redesign.
5. After testing, discuss which gear ratios worked best for each course. When does in benefit to have more torque? When was it beneficial to have more speed?

Extensions and Modifications:

• Create a third course. This course could be:
• Half flat and half inclined
• A downhill course
• How steep can the ramp be?
• How fast can the car go up the incline? Can you make it faster?
• What gear ratio would be best for this course?
• For context/a story, tell the students that there is an injured hiker trapped on a mountain. The students need to design a car that will be able to drive up the side of the mountain to rescue the hiker! What gear ratios would be best for going up a mountain?
• Build a car that can make it up the ramp and tow a weight along with it.

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