DENJIRO: Many of you ride a bicycle. You can see that this part is at an angle. This is called the “caster angle.” Now, why is it at an angle? Here, we have prepared a bicycle with a caster angle and one without a caster angle for an experiment. First, let’s try pushing the bicycle with the caster angle. It moved in a straight line on its own without falling over. Now, let’s try pushing the bicycle without a caster angle in the same way.
GIRL: It fell over!
DENJIRO: In fact, bicycles are able to maintain balance and move on their own because of the caster angle. In order for a bicycle to move without falling over, the front tire needs to turn in the same direction that the frame tilts to. When you tilt a bicycle with a caster angle… you can see the tire and handle turn. In other words, the caster angle allows the handle to naturally turn in the direction that the bicycle tilts to and makes it easier for the bicycle to stay balanced.
The caster angle also serves another purpose. By having the contact point on the front tire behind the bicycle’s rotation axis, the bicycle is able to return to the center even if the front tire slants, and it can easily move in a straight line. A push cart uses this property. In most cases, the back tires of a push cart are fixed while the front tires rotate. The contact point of the front tire is behind the rotation axis, increasing its ability to move in a straight line. This is why the push cart steadily moves in a straight line even after you push and let go.
NARRATOR: When you look at the front tires of the push cart, you can see that they are straight.
DENJIRO: You can easily carry things because the front tires are stable. I hope energy will bring you all happiness. Our magic word is "Happy Energy!”