An example of friction…(Don’t do this)

I recently found myself walking around in Christmas Tree Shops, a store which is notorious for being one of the most annoying places to shop, and I noticed a trend there that I want to make everybody aware of, because you’re doing it all wrong.

Many markets and shops provide shopping carts for your convenience. You know, the ones that look like this:

These wagons have wheels because application of a force will set the wheel in motion hereby setting the cart in motion. If the carts had no wheels, the initial static friction to get the wagon moving followed by the continual kinetic friction to keep the wagon in motion would be too difficult for a human being to overcome. It would also result in damaged floors and short wagon lifetimes.

So they have manufactured these high tech wagons to help us in our shopping. Luckily, when we go shopping, we are loading a fairly insignificant weight of goods into our wagon, but, as the wagon starts to fill up, we notice it gets harder to push. Not to go into a detailed explanation of vectors, but this is because the gravitational force of the goods is directly downward.

When we push our carts, optimally, we want to push horizontally, exactly 90 degrees opposite the force due to gravity. That’s because, if we don’t, we are wasting the force we exert. Here’s some conceptual, mathematical (trigonometric) proof.

Let’s say we’re pushing a cart to the left, and we exert a force, “c” to the cart. If we push completely parallel to the floor, 100% of the force goes into setting the wheels in motion.

Let’s say we exert the same amount of force of “2” to the cart, but do so with the trajectory depicted in the following diagram (down and left):

Just visualizing the vectors, you can see, that exerting force in that direction significantly decreases the resulting horizontal component of your force and adds a force directly downward, which will impede motion of the wheels. If a 180 lb person does this, this could be very significant!

So I just want you to know, when you’re slouching around the store with your arms draped over the handlebar and it looks like you’re about to fall asleep on top of the handlebar, you’re making it more difficult on yourself to push the wagon.

Stand up straight, arms directly in front of you, and push the damn thing straight ahead. You’ll get out of my way a lot faster, and you’ll save a lot of energy!