If humans could fly, without tools and machines, how fast do you think we would go? As of 2012, the world record for fastest short-distance sprint speed is roughly 27 miles per hour. Running speed depends on how much force is exerted by the runner's legs, and according to Newton's Second Law of Motion, force is the product of mass times acceleration. And Newton's Third Law states that for every action, there is an equal and opposite reaction. So, that means running requires having a ground to push off from, and the ground pushes back against the runner's foot. So, flying would actually be more similar to swimming. Michael Phelps is currently the fastest human in water and the most decorated Olympian of all time. Guess how fast he swims? The answer may surprise you. His fastest recorded speed is less than 5 miles per hour. A child on the ground can easily outrun Michael Phelps in water, but why is that? Well, let's go back to Newton's Third Law of Motion. When we run, we move forward by pushing against the ground with our feet and the ground pushes back, propelling us forward. The ground is solid. By definition, it means the particles are essentially locked into place and must push back instead of getting out of the way, but water is liquid and flows easily. When we move our limbs to push back against the water, a part of the water molecules can just slide past one another instead of pushing back. Now, let's think about flying. Air has a lot more free space for particles to move past one another, so even more of our energy would be wasted. We would need to push a lot of air backwards in order to move forward. Astronauts move around in shuttles in zero gravity when they're in outer space by pulling on handles installed on the ceiling walls and floors of the shuttle. Now, imagine you were given the ability to float. How would you move around in the middle of the street? Well, you wouldn't get very far by swimming in air, would you? Nah, I don't think so! Now, assuming you were granted the ability to float and the speed to move around efficiently, let's discuss the height of your flight. According to the Ideal Gas Law, P-V N-R-T, pressure and temperature has a positive correlation, meaning they increase and decrease together. This is because the air expands in volume with less pressure, so the molecules have more room to wander around without colliding into each other and creating heat. Since the atmospheric pressure is a lot lower in high altitudes, it would be freezing cold if you were flying above the clouds. You'd need to wrap yourself up to keep your core body temperature above 95 degrees Fahrenheit, otherwise you'd start shivering violently, gradually becoming mentally confused and eventually drop out of the sky due to loss of muscle control from hypothermia! Now, the Ideal Gas Law implies that as the pressure decreases, gas volume increases. So, if you were to fly straight up too quickly, the inert gas in your body would rapidly expand the way soda fizzes up when shaken. The phenomenon is called "the bends," decompression sickness, or "divers disease" since deep sea scuba divers experience this when they come up too quickly. This results in pain, paralysis, or death, depending on how foamy your blood becomes. Okay, well, let's say you want to fly just a few meters above the ground where you can still see the road signs and breath oxygen with ease. You'll still need goggles and a helmet to protect you from birds, insects, street signs, electrical wires, and other flying humans, including flying cops ready to hand you a ticket if you don't follow the flying rules, buddy. Now remember, if you have a collision mid-air that knocks you unconscious, you would experience free fall until you hit the ground. Without society or the laws of physics, flying would be a totally awesome ability to have. But, even if we could all just float around a few feet above the ground and only moving at a snail's pace, I'm telling you, it's still a cool ability that I'd want, wouldn't you? Yeah, I thought so. Now, which superpower physics lesson will you explore next? Shifting body size and content, super speed, flight, super strength, immortality, and invisibility.