Numbers Only on Google Forms

I am currently working on a version of Mean Paper Airplanes that I found on Julie Reulbach's blog and came across her comment to Dan Meyer about Google Form Functionality:

I was excited to find that Google has added this feature in its most significant form overhaul for education: data validation. Forms also now have the ability to post images and video, which is awesome (I am going to make interactive modules with videos and images of tables, graphs and patterns for questions). 

I wanted to show how Google Forms can be set to fix her issue.  

When writing the question, notice the "advanced settings" tab at the bottom:

Click "data validation" and selected the "number" option and specify "is number" so that only numbers can be entered. Then I select an error message to pop up if students type in something else, like the units of measurement. The message I chose was, "only enter the number of inches."

From the student's perspective, they would see this if they typed in units:

There is so much more that can be done with data validation. I can't wait to play around with it more this summer.

Thanks Julie for finding that lesson, it has been really fun so far!  (I will post my extensions to it as it is amazing and fits nicely with the 8th and 9th grade CCSS curriculum as well)