Name of Activity Tow Truck
Author STOMP
Keywords steep, ramp, tow, towing, weight, gears, gear up, gear down, building, design, friction, gravity, center of gravity
Subject NXTs
Grade Level 4, 5, 6, 7, 8, 9+
Time 1 Hour Total
Brief Description Build a car that can climb a steep ramp while towing a weight (10 batteries) behind it.
Using gears to gear down is necessary for this challenge. This activity is more challenging
than a regular ramp climb and may require some complex building and design.
Lesson Objectives: – To learn to build and use gears.
– To learn about gravity, center of gravity, and friction.
Materials Needed: NXT kits
batteries for weight
computers running NXT Software
Preparation and Set Up: Build a ramp.

Set up computers running NXT software.

Arrange student in groups of two.
Distribute necessary materials.

Necessary Background It is more difficult for cars to climb steep slopes for different reasons. In this lesson you
can discuss with the class these different forces that affect the ability of the car to
climb the slope:

Friction – friction is the force acting between the surfaces of the car (tires) and
the ramp surface. This is the force that keeps the car from slipping.
Gravity – gravity pulls down directly towards the center of the earth. On a flat
surface gravity does not pull a car in any direction, but just keeps it in place. On
a slope, gravity pulls a car backwards towards the center of the earth down the ramp.
Center of gravity – Center of gravity is the exact spot on an object where there
is the same amount of weight on one side of the spot as there is on the opposite
side. A high center of gravity means a car is more unstable on a steep slope.
A low center of gravity close to a ramp will help the car stay on the ramp.To
overcome these forces there are several things that you can do to your car:
Low center of gravity – design the car to be low to the ground.
Gear down the car – By adding gears to the motors and then gearing to the
wheel you can increase the power of the motors, which will help the car climb
the ramp. There is more information about gears and gear worksheets in the
attached documents.

Gear Ratios
Center of Gravity

  1. Have students design and build a car that will climb a ramp.
    1. Students will need to think about friction and center of gravity to build their car. If students are unfamiliar with these concepts, you should review the concepts with them. A car that is lower to the ground will be less likely to slip. Wheels that have more traction and greater surface area on the ramp will also be less likely to slip.
    2. Students will need to use gears to gain more power. If students are unfamiliar with using gears, you should review gears and gearing down with the students.
  2. Have students program their cars to move forward for 20 seconds.
  3. Allow students to test their cars on the ramp without anything in tow.
  4. Students should redesign the car if it does not climb the ramp.
  5. Students should then test their cars while towing the weight up the ramp and redesign until the car can tow the weight.
  6. If students have trouble tell them to try various gears, wheels and designs.
Extensions: What is the steepest ramp that the car can climb?
What is the heaviest weight that the car can tow?
Calculate the gear ratio.
What is the quickest that the car can travel up the ramp?
Reference 1
Reference 2
Reference 3
Reference 4
Reference 5
Reference 6
Reference 7
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