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. If you’re on one of those spinny theme park
rides where the floor drops out, or take a really sharp turn in a car, it 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, basically, we want more
air molecules hitting the bottom of the plane than the top. 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, 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 lightbulb, 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 lightbulb 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 lightbulb. 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 lightbulb 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. Thanks for watching this episode of SciShow,
brought to you by our patrons on Patreon. If you want to help support this show, just
go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow and subscribe!
I don't like this "Centrifugal Force is not a real force", simply because it is a result of acceleration. It can be measured, it can be calculated. And gravity is just a result of the curvature of spacetime. Does that mean that gravity isn't a real force too?