A two-legged robot like Zowi needs to be careful where it puts its feet, otherwise it could fall.


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Did you know?

It’s not just the Earth which is attracting you. It might seem hard to imagine, but all the objects around you right now are attracting you and you are attracting them. However, this attraction is very slight.

Experiment 1 – Gravity

Let’s start by finding out the centre of gravity of a ruler.
The centre of gravity is right in the middle. Do you know why? Because at this point, neither half of the ruler weighs more than the other.


Let’s check it out:

  1. Grab a ruler.
  2. Place the ruler on the edge of a table, with most of the ruler resting on the table. Gradually move it toward the edge and see when it falls.
  3. At what measurement did it fall? You’ll see that when the centre of gravity is not resting on the table, the ruler falls.
regla12 regla13 regla14

Cuando el centro de gravedad se queda sin apoyo, la gravedad tira de ella hacia abajo, haciendo que la regla se caiga.

Did you know?

It is said that gravity was discovered by a scientist named Isaac Newton around 350 years ago. Newton was leaning on an apple tree when he saw an apple fall in front of him. He suddenly realised that all objects attract each other: the Theory of Gravity.

However, we still know little about this mysterious force, and other scientists like Albert Einstein have made great discoveries. The last big discovery was very recent, in February 2016.

Experiment 2 – Zowi’s Gravity

Now let’s do a similar experiment with Zowi. Zowi’s head weighs more than its legs, so its centre of gravity is not in the middle, but between its eyes.
Again, this is the point at which both sides of the object weigh the same. Let’s check it out!



¡Vamos a comprobarlo!

  1. Take Zowi and switch it off.
  2. When Zowi’s centre of gravity is between its legs, it is stable.
  3. APP-ZOWI-1

  4. Gradually push it to one side.
  5. Even when its centre of gravity goes over one leg, Zowi remains balanced.
  6. APP-ZOWI-2

  7. When the centre of Zowi’s head goes below the support area (the foot), Zowi falls over!
  8. APP-ZOWI-3

  9. The same thing happens with you. Try and imitate Zowi! Your centre of gravity is just above your belly button. You’ll see that when this point goes below your support area (your foot), you fall over.
  10. grav-human2

The centre of gravity is a very important factor to take into account when designing a robot, as this affects its movement. If the centre of gravity moves out of the base of support, the robot will fall.

Moment of inspiration !

Find the centre of gravity of other objects you have at home and check if what you’ve learned is true. Can you balance a stick on your palm? When does the stick fall?