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You probably don’t think a lot about your shoes. If you’re like most people, you worry about whether they look good, whether they’re comfortable, and then you just put them on when you need them. But there are people who think a lot about their shoes: athletes. They need to have specific shoes for specific sports, and shoe manufacturers know that. In fact, shoe companies probably think about shoes more than anyone else, because it’s their job to understand how people move in different situations in order to design the best shoes for those situations. Shoes have to absorb shock and protect your feet, and your feet move and impact the ground differently in, say, sprinting and playing tennis.
Today we’re going to focus on running shoes, and compare them to some other types of footwear in a classic physics experiment: the egg drop.
Materials:
- Eggs
- Ziploc bags
- Shoes
- Running shoes are a must for this. Comparison options include…
- Thin-soled shoes like Converse All-Stars or ballerina flats
- Men’s dress shoes
- Snow boots
- Flip-flops or sandals
- Just a plain old sock
- Tape (optional)
Process:
- Let’s start by ensuring a minimal mess: put each of your eggs into a Ziploc bag and seal them up tight. We’re going to be dropping them, and we don’t want the yolk to get everywhere.
- Make a decision about how high you want to drop from. I recommend as high as you can hold the shoe, but whatever your height is, keep it the same for each trial.
- Put one of your bagged eggs into your running shoe near the heel. Tape it in if it looks like it wants to fall out.
- Drop your running shoe flat onto the ground, with the sole facing down, so the egg is protected inside the shoe.
- Pull out your egg and observe it. How did it do? Is it intact? Cracked a bit? Completely shattered?
- Now repeat that process with your other types of shoes, dropping and observing. Some will protect the shoe better than others. If you want to try a flip-flop, you’ll definitely have to tape the bagged egg down.
- Compare your eggs. Which shoes protected them better? Which ones didn’t do so well, resulting in a bag full of raw egg?
Summary
Have a look at that running shoe. See how thick and chunky the heel is? Other shoes have thick heels, like boots and some men’s dress shoes, but running shoe heels are different. Reach into the heel and press down hard with a couple of fingers. Feel how the heel compresses under pressure? That’s one of the man design features of a running shoe.
Most types of shoes are made of two main parts: the upper (which, as it sounds, is the top part that encases the foot) and the sole (the whole bottom part). Lots of research goes into the soles to determine the best sole structure for different activities. A running shoe sole has four main parts. First, there’s the outsole, the rubber on the bottom. Then there’s the insole, the thin foot-shaped piece inside the shoe that you can sometimes even pull out. Then there’s the midsole, a layer between the two which is usually made of a specially designed foam to help cushion your foot when it hits the ground during a run. Finally, there’s the heel wedge, which is one of the things that makes running shoes different from other kinds of athletic shoes, like tennis shoes or Converse All-Stars.
The heel wedge is a thick, wedge-shaped layer of foam that’s also between the insole and outsole, and its job is to add extra protection to the heel. The foam absorbs some of the energy of your heel hitting the ground when you run. See, when your heel hits the ground, the ground also hits your heel, and all that ground force can cause injuries without enough cushioning. Different organizations and companies have done a lot of study on the physics of running and found that a runner’s foot can hit the ground with up to 3 times their body weight in force!
Tennis shoes have more even cushioning because tennis players don’t just run forward and hit the ground with their heels; they’re moving backward, side to side, and taking small steps and big lunges and everything in between. Their shoes need to reflect that. Work boots need decent cushioning but need a strong upper to protect the foot from other issues. For every need, a shoe, and for every shoe, a purpose.
Now, it's time to lace up your shoes and head out to the Riley Children's Health Sports Legends Experience for some fun! Want more Saturday Science? See all of our at-home activities on the blog or on Pinterest.
