When I was in Chile, the third step in at least 90% of conversations I held (at least with new people) concerned my major: Where are you from? -> Why are you here? -> Oh, what do you study? I had a strong incentive to derail this conversation train because I knew I was going to mangle the word for engineering irreparably, but I usually wasn't successful. After we finally got through my stumbling through "ingenería", the rest of the conversation proceeded apace (in Spanish):
"Oh, can you fix my car?"
Halfway through the semester, someone explained to me that the word I was using for mechanical (engineer) was really (shop) mechanic. What I really was, is a "civil engineer" - the opposite being a "commercial engineer" in management/business.
But really, even in a language I'm certain about, I get asked to fix a lot of things once I'm identified as an engineer. I love it. Engineering is technical problem-solving; we fix things - processes, machines, tools, paradigms, your great-aunt's computer, whatever you've got.
But especially your great-aunt's computer. Why? Well, because you're an engineer and it's your family, and I just can't resist that combination. So when I go home, I love it when my family suggests things to fix - and this time they had a more out-of-the-ordinary problem: how can a person with minimal muscle strength play with their 70-lb dog?
Keep reading for the answer...
(I will also accept "levers!" because that's a pretty safe answer to any mechE question, and really, pulleys are pretty much just a way of doubling over a flexible lever).
Here's a 1st prototype I rigged up after a quick visit to a hardware store.
Systems of pulleys are awesome. They let you trade distance (how far you pull your end of the rope) for force (how hard you have to pull to exert a desired force on the other end). In the pictures above, the pulley in the right-hand corner is attached to a large post as an anchor (by the black strap). The dog is pulling on a toy attached to the second pulley, and a person is pulling on the line pointing to the left.
Here's a simplified diagram. Basically, the force of the dog pulling is now split between the rope going to the person, and the rope going to the anchor - so to win this game of tug-of-war, the person needs to be pulling just more than 1/2 as hard as the dog.
I think before I came to Olin I would have been much less likely to actually build something like this. Not that it really required any particularly difficult technical skills, but I hadn't quite realized I could just go get stuff and make a rough draft of an idea. But after 3 (and counting) years filled with projects and a "bias to action" (better to do something and fail than not do it at all - within limits!), it just seemed natural to me to pull together a prototype and see if I could actually make it work, instead of just thinking about it. And I think Aston (the dog) agrees: