Engineering 100-980

Lab 8: Terminal Velocity and Drop Tests

Contents

Resources

Although you have been given teams, this lab is done in partners and submitted individually. Break into groups of two (your partner may be in your assigned team, but this is not required) and gather data together. You should both submit separate PDFs.

Introduction

Galileo Galilei, a 16th century astronomer, philosopher, mathematician, and central figure in the Scientific Revolution of the 17th Century, once wrote that, in the absence of resistance caused by air, a hammer and a feather would fall at the same rate. His claim was verified centuries later on the moon by the crew of Apollo 15, which is also known as the all-UMich Apollo astronaut crew. You can watch the demonstration in the video Hammer vs Feather - Physics on the moon.

This phenomena is not random, and is instead due to drag forces. While we know that the acceleration due to gravity is constant for all objects, we also know that not all objects fall at the same rate, even if it seems they should. This is because of drag force, which is related to properties of the object as well as the cross-sectional area of the object. Terminal velocity is the maximum speed an object can reach while in free-fall. Historically, we have used this to our advantage with the use of parachutes to lead to safe fall speeds for things like payloads, or even humans.

The Drag Equation

Reference Area

In the case of an object attached to a parachute, we can consider the object as a projectile with no thrust and starts from a y-position of greater than 0. We also need to incorporate drag force into our standard projectile equations to help us determine when the object will reach its terminal velocity. We have provided a starter spreadsheet that integrates these concepts of drag and terminal velocity.

Terminal velocity is when the drag force is equal to the weight of the object, as noted below:

Terminal Velocity

Procedure

Setup

  1. Measure your parachute’s diameter and calculate its area. Store this value in the spreadsheet.

  2. Record your parachute’s mass (with the army guy) and record this value in the spreadsheet.

  3. Measure ONE binder clip and record this mass in your spreadsheet.

  4. Measure the mass of your 45” roll of streamer tape and record this value in the spreadsheet.

For consistency, measure the mass of one binder clip and for each iteration with a different total mass, make sure to use the same kind and size of binder clip. Then you can simply multiply the number of clips and add the mass of the parachute for each iteration to find the total mass rather than re-weighing the entire system for every trial.

Parachute Trials

To start, we are going to measure the terminal velocity of your parachute setup with two separate mass configurations, and create a similar plot to your sensor calibration curves. We have created a spreadsheet for you to record your values in.

Robotics Dimensions

Streamer Trials

Next, we are going to perform similar trials using streamers. The concept of streamers is similar… but different… from parachutes. The object of streamers is to make a strip of material (often mylar in model rocketry) flap around in the wind and expose as much of its surface area to the air it’s travelling through. Parachutes have a property of “catching” the air and allowing it to spill over its edges creating drag while also maintaining a steady attitude. Streamers, on the other hand, create enough drag to keep the object falling in a constant orientation, but don’t provide nearly as much drag. We will observe this in the following procedure.

Computations

Submission

Although you have been given teams, this lab is done in partners and submitted individually. You and your partner should both submit separate PDFs.

On Canvas, you will submit ONE PDF that will include all of the following:

To put said content into a PDF, it is suggested you create a new Google Doc (docs.new) and paste your images and write any text in the document. Export/Download this document as a PDF and upload it. DO NOT SUBMIT A GOOGLE DOC FILE OR SPREADSHEET FILES.

Submitting anything other than a single PDF may result in your work not being graded or your scores being heavily delayed.

Separately: