# Study Kinetic Energy with a Rube Goldberg Machine

## Summary

## Overview

Rube Goldberg machines—machines that complete a simple task in a convoluted way—are intriguing, artistic, and fun! In this lesson, students will design and build such a machine themselves and use the concept of kinetic energy in the process. Before students start designing, they will do an experiment that explores how kinetic energy depends on the mass and the speed of the moving object. With a clear understanding of this concept, students then tackle the engineering design process. Watch how students channel their creative energy into constructing a fun and exciting machine!

## Learning Objectives

- Understand that the kinetic energy of a moving object is proportional to its mass, or, that kinetic energy of the object doubles when its mass doubles.
- Understand that the kinetic energy of a moving object is proportional to the square of the speed of the moving object, or, that the kinetic energy of the object quadruples when its speed doubles.
- Apply the concept of kinetic energy to moving parts of a Rube Goldberg machine.
- Experience the importance of planning in the engineering design process.
- Explain how knowledge of scientific principles can help shorten the engineering design process.

## NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:- MS-PS3-1. Construct and interpret graphical displays of data to describe the relationships of kinetic energy to the mass of an object and to the speed of an object.
- MS-ETS1-1. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

Science & Engineering Practices | Disciplinary Core Ideas | Crosscutting Concepts | |||

Science & Engineering Practices | Asking Questions and Defining Problems.
Define a design problem that can be solved through the development of an object, tool, process or system and includes multiple criteria and constraints, including scientific knowledge that may limit possible solutions.
Analyzing and Interpreting Data. Construct and interpret graphical displays of data to identify linear and nonlinear relationships. |
Disciplinary Core Ideas | PS3.A: Definitions of Energy.
Motion energy is properly called kinetic energy; it is proportional to the mass of the moving object and grows with the square of its speed.
ETS1.A: Defining and Delimiting Engineering Problems. The more precisely a design task's criteria and constraints can be defined, the more likely it is that the designed solution will be successful. Specification of constraints includes consideration of scientific principles and other relevant knowledge that are likely to limit possible solutions. ETS1.B:: Developing Possible Solutions. A solution needs to be tested, and then modified on the basis of the test results, in order to improve it. |
Crosscutting Concepts | Scale, Proportion, and Quantity.
Proportional relationships (e.g. speed as the ratio of distance traveled to time taken) among different types of quantities provide information about the magnitude of properties and processes. |

## Materials

**Part 1: Experimental Exploration of Kinetic Energy**

Per group of 3–4 students:

- Meterstick
- Marbles (3)
- Small disposable cup
- Pennies (2)
- Scissors
- Painter's tape
- Insulation tape
- Small box or stack of books to prop up the ramp

** Part 2: Building a Rube Goldberg Machine**

This is an engineering design project, so there is not a specific list of required materials. You can make different materials available to your students or allow them to bring materials from home. In general, recycled items, craft supplies, and office supplies work well.

Options for materials to construct parts:

- Cardboard (cereal box, shoe box, cardboard panels, etc.)
- Tubes (cardboard, plastic, insulation tubes, etc.)
- Paper, plastic, aluminum foil
- Disposable cups, any size
- Soda or water bottles or cans
- Funnels
- Wooden dowels, craft sticks, chopsticks, skewers, plastic cutlery
- Building blocks
- Ruler
- Balloons
- Bells
- Dominoes
- Fan
- Ice cubes

Options for materials that connect parts:

- Painter's tape
- Glue (a hot glue gun works well)
- Rubber bands
- Thread

Options for materials that roll:

- A variety of balls of different masses, like marbles, ball bearings, ping pong balls, tennis balls, pool balls, etc.
- Toy cars
- Roller skates
- Thread

Options for adding chemistry:

- Vinegar and baking soda
- Effervescent tablets (avoid medication!) and water

## Background Information for Teachers

*This section contains a quick review for teachers of the science and concepts covered in this lesson.*

**Kinetic energy**, also called the energy of movement, is the amount of energy an object has due to its mass and its speed. In science, energy refers to the ability to create change (e.g. lift an object, deform an object, warm up a material, etc). The change a moving object can create is a measure of its kinetic energy. In this lesson, students will roll marbles down a ramp and use the distance over which a cup placed in the marble's path can be pushed as a measure of the marble's kinetic energy. Increasing the number of marbles allows students to study the impact of mass. Students will see that kinetic energy is proportional to mass. Students know this from experience, as they know that a heavy brick falling onto a foot can create more damage compared to a light plastic brick falling onto a foot from the same height.

Letting the marble(s) roll from different heights along the ramp, together with a graph showing the correlation between starting position and speed, allows students to explore how kinetic energy correlates with the speed of an object. A detailed analysis of the data will reveal that kinetic energy is proportional to the square of the speed of the moving object, or, for less mathematically inclined classes, that that kinetic energy quadruples when the speed doubles. Students also know this from experience, as they know that objects that move faster can create a lot more damage and thus, have a lot more kinetic energy. A shopping cart crashing at a slightly higher speed into a car can do a lot more damage than a shopping car that slowly rolls into a car. Or, a small increase in a car's speed quickly creates a much more severe car crash.

Once students have explored the concept of kinetic energy, they will use it to design a **Rube Goldberg machine**. Rube Goldberg machines are named after the American cartoonist, author, engineer, and inventor Rube Goldberg (1883-1979). According to Webster's New World Dictionary, a Rube Goldberg machine is "a comically involved, complicated invention, laboriously contrived to perform a simple operation." Rube Goldberg drew many of these machines. Usually, they are a series of simple contraptions, each of which triggers the initiation of the next, achieving the completion of a simple task in a convoluted and complicated way.

Many concepts studied in physics can be explored using Rube Goldberg machines; this lesson highlights kinetic energy. Several of the simple contraptions will have moving parts, and kinetic energy is often an accessible way to understand why they can trigger the next contraption, and if needed, how to make adjustments. For example, a sickle will need to swing fast enough, or be heavy enough, to have the energy it takes to cut a rope. A marble will need to roll fast enough or be heavy enough to have enough energy to knock over a domino. Students will use the concept of kinetic energy in the planning phase, the iterative improvement phase, and while communicating their results.