 Vernier Software & Technology

# Mechanical Power

## Introduction

You have been introduced to energy as something that is involved in making things happen. Energy can be transferred or transformed between objects, materials, and ways of accounting for energy. For example, the act of stretching a rubber band transfers energy into the rubber band, which we call elastic potential energy. Elastic because it is related to the stretchiness of the rubber band and potential energy because as long as the rubber band remains stretched, the energy is stored but available for use. Releasing the rubber band in a certain way so as to project the rubber band through the air allows the elastic potential energy to transform into kinetic energy (the energy associated with motion).

To stretch the rubber band, a force is applied to part of the rubber band, which causes part of the rubber band to move a certain distance. Whenever a force moves an object some distance, we say that mechanical work is done. Mechanical work, like energy, is measured in joules (J). Work is one way to transfer or transform energy.

Just as you can do work to stretch a rubber band, you can also do work to lift a weight. In order to lift an object from a lower position to a higher position, a vertical force must be applied. In this case, the work done gives the object moved upward gravitational potential energy, because instead of being pulled against a stretchy material, the object is moved against the direction of the force of gravity. In this experiment, you will use a wind turbine to lift an object (a bucket of washers) from a lower position to a higher position.

Power is defined as the rate at which energy is used, applied, or transformed. It is also the rate at which work is done. If an amount of energy is analogous to a specific distance, power is analogous to speed, which is the rate at which an object travels a distance. The faster an object is lifted, the more power is being used. The unit of power is the watt (W), which is equivalent to one joule per second (J/s).

In this experiment, you will calculate power using the equation $\text{power} = \frac{\text{amount of work done}}{\text{how long it took}}$

You will use a wind turbine to do the work of lifting a mass. You will vary the pitch (angle) of the blades of the wind turbine and measure the time it takes to lift a mass a given distance. Based on these measurements, you will calculate the mechanical power generated by the turbine as it lifts the weights.

## Objectives

• Identify the units that are used to measure power.
• Measure the power generated by a wind turbine.
• Determine the relationship between wind turbine blade pitch and power generated.

## Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

You may also need an interface and software for data collection. What do I need for data collection?

## Renewable Energy with Vernier

See other experiments from the lab book.

 1 Renewable Energy: Why is it So Important? 2 What is Energy? 3 Project: Energy Audit 4 Voltage and Circuits 5 Current and Resistors 6 Mechanical Power 7 Generators 8 Exploring Wind Turbines 9 Effect of Load on Wind Turbine Output 10 Blade Variables and Power Output 11 Solidity 12 Turbine Efficiency 13 Power Curves 14 Power and Energy 15 Project: Maximum Energy Output 16 Project: Build a Wind Farm 17 Exploring Solar Panels 18A Effect of Load on Solar Panel Output 18B Fill Factor and IV Curve of a Solar Panel 19 Variables Affecting Solar Panel Output 20 Effect of Temperature on Solar Panel Output 21 Project: Build a Solar Charger 22 Exploring Passive Solar Heating 23 Variables Affecting Passive Solar Heating 24 Exploring Solar Collectors 25 Variables Affecting Solar Collectors 26 Project: Solar Cooker

### Experiment 6 from Renewable Energy with Vernier Lab Book #### Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.