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Bumblebees fly, lights turn on, and you can ride a bike without falling over. We all know these things to be true, but what you may not know is the real reason behind why they work. Join Olivia to bust seven myths about motion.

Hosted by: Olivia Gordon
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Centrifugal Force
Olivia: You move everyday, and I’m not just talking about exercise or your daily commute. Every atom in your body is vibrating, and you’re on a planet that’s speeding around the Sun, while the universe is rapidly expanding. And for all the moving we do, we don’t always know how things get from Point A to Point B. So we’re gonna debunk seven common misconceptions about moving things, and explain what’s really physically going on.

[SciShow intro plays]

If you’re on one of those spinny theme park rides where the floor drops out, or you take a really sharp turn in a car, you might feel like you’re being pushed against a wall. Lots of people call this centrifugal force, but the truth is, there is no centrifugal force trying to push you outward.

Like, let’s say you’re riding in a car down a long, straight road, which means both your body and the car are moving forward pretty fast in one direction. And, all of a sudden, the car turns left. Because you’re not a part of the car, your body still tends to go straight even though the car is turning, and this tendency is called inertia.

So when the car turns, you basically end up crashing into the side of the car, so you’re forced to change directions and make the turn with it. It feels like there’s some kinda force trying to push you outwards, but really, you were already travelling in the outwards-direction and the wall is just trying to keep you in.

Even though bikes have been around since the early 1800s, there are still misconceptions going around about how bikes work. We all know if you hold a bike still, and then let go, it just falls over. But if a bike is moving, it can glide along gracefully and accident-free, even if there’s no human on board. That leads people to think that a bike stays upright simply because it’s moving forward fast enough... but it’s a little more complicated than that.

Turns out, there are lots of physical factors that work together to help bikes stay upright. And one important thing is the position and mass of the front wheel and handlebars. The front wheel of a bike is slightly in front of the handlebars, so that the turning axis is at an angle.

Plus, the weight of the front wheel and handlebars is generally towards the front of the bike, concentrated slightly in front of this turning axis. These things mean if the bike starts to fall to the left, for example, the wheel will automatically turn to the left. So the bike can basically correct itself and stay balanced, as long as it has enough speed so that the wheel can roll and move back under the bike’s center of mass.

This is also why people can steer bikes without their hands: you just lean your body in one direction, and the wheel will naturally turn in the same direction. But there’s other factors that help conventional bikes steer, such as the gyroscopic effect, which happens when you have a spinning object, like a wheel. When a force pushes down and left on a spinning wheel, the push will also cause torque, the ability to make something rotate, making the wheel turn left. With all these different features playing small parts, bikes are really just designed to keep their wheels beneath their riders.

For planes to fly, they need to create a lift force which is at least as strong as the force of gravity. And lift force is created when there’s a pressure difference between the bottom and the top of the plane. Now the question is: what makes this pressure difference? There’s a myth going around that’s become so popular, it even got its own name: the equal-transit fallacy.

The idea is that when air is sliced by an airplane wing, some air travels above the wing and some air travels below the wing. Now because the top of the wing of most planes is designed to be longer than the bottom, the air has to travel a farther distance before the air reunites on the other end. Because the air has to travel farther, it goes faster. And something called Bernoulli’s principle shows us that faster moving air means less exerted pressure. So, the top will have a lower air pressure than the bottom, and the plane will fly.

So simple! But... not quite. That explanation doesn’t actually add up. It’s true that the air on top of the wings moves faster than the air underneath, but this normally doesn’t create enough pressure difference to lift a whole plane.

Really, it’s because of the fast-moving air above the airplane wings plus the fact that wings are typically tilted slightly upwards and curved. This causes much more air to hit the bottom of the wing and prevents air from hitting the top of the wing, pushing the plane upwards.

In the early 20th century, there was a misconception going around that bumblebees shouldn’t be capable of flight. Now obviously we know they are capable of flight because... well... they fly. But based on calculations using aerodynamic theories from the 1930s, it seemed impossible because their wings were too small to create enough lift.

But the missing key was how the bees actually used their wings. Bees don’t actually flap their wings up and down, they’re moving their wings back and forth, while also rotating them. Basically, they’re trying to create a pressure difference so that there’s lift. But instead of working like plane wings to force air downward, they swirl the air and make small vortices, which looks like a mini-hurricane with low pressure in the middle.

The wings move so that a vortex forms and creates a low pressure region above their wings, and the pressure difference creates enough lift for the bee to fly! So bees used to confuse the world’s physicists, but now we have a much better understanding of how fluid dynamics work to keep their chubby bodies in the air.

When you see astronauts up in space, they appear weightless and you might think that they’re just floating around gravity-free. But actually, gravity is everywhere, and it can be pretty strong in space! Gravity is a force that pulls any two objects with mass in the universe towards each other. Even you and your friend standing next to you are being slightly pulled together by gravity. And the more mass you have, the stronger your gravitational field.

So the Earth has plenty of mass, and the force of gravity really does pull astronauts towards the Earth as they orbit it, but they don’t crash into the ground. The key is that astronauts are also moving so fast sideways that they’re falling and missing the ground. The reason they don’t even notice the gravity is because everything else is also falling around them too, like the floor, and their food and their fellow astronaut friends. So if everything is falling, it’s almost as if nothing is. Except for maybe a few people falling for this misconception.

When you turn on a light bulb, you see the light turn on almost instantaneously. And electricity is the flow of electrons in a wire. So you might think that electrons are moving super, super fast, and travel all the way from the battery to the light bulb in a matter of milliseconds, right? Well no. The electrons are actually moving super slow down a wire, like, slower than a minute hand moves on a clock.

See, the wire is already filled with electrons. And because the wire is conductive, some of these electrons are free to travel around When the light switch is off, this electron movement is pretty random, with no particular goal. When the light switch is off, this electron movement is pretty random, with no particular goal. But when you turn the light switch on, you complete a full circuit between the positive and negative terminals of a battery.

Now, we know that opposite charges attract each other, and similar charges repel. And because electrons are negatively charged, they’ll favor moving towards the positive terminal, which will be either towards or away from the light bulb. We call that small movement the electron drift velocity.

However, there’s also something called a signal velocity, which tells us how long it takes for the light bulb to feel the effects of this force, and light up. You can imagine signal velocity kind of like a long line of people kind of squished together. If the person at the back pushes forward a little bit, it’ll cause a domino effect where all the people in the line move slightly forward.

Nobody moved very fast, or very far, but the signal travelled through the line very quickly. In a typical cable, the signal moves at about two-thirds the speed of light. So almost instantaneously, the electrons in the light bulb start moving slightly, causing the filament to glow!

If a penny fell from a really tall skyscraper, like the Burj Khalifa in Dubai, would it fall fast enough seriously hurt someone walking on the street? Luckily, the answer is no. The big misconception comes from thinking that objects keep accelerating when they fall, and they do for a little while, but not forever! As the penny gets faster and faster, it starts to experience more and more drag, basically air molecules hitting the penny and slowing it down.

Pennies don’t have a very aerodynamic shape, so they experience a lot of this air resistance. Also pennies are pretty light, which means it doesn’t take much air resistance to counteract the force of gravity. When the air resistance is as strong as gravity, the penny won’t fall any faster no matter how far it falls, it’ll reach its maximum speed, called its terminal velocity.

In fact, different researchers have experimented with throwing pennies off of skyscrapers, and found that pennies reach their terminal velocity after about 15 meters. So whether it’s a 5-story building, or a 50-story building, the penny will be going at the same speed, which depends on the conditions outside, but can be around 50 kilometers per hour. For the poor person below, a falling penny would just feel kinda like a flick to the forehead.

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