Why cant you stand with one leg lifted and the other with ankle and shoulder touching the wall?
Can you stand with one leg lifted and the other with ankle and shoulder touching the wall?
Just do this activity. Go against a flat wall and stand along the wall so that one side of your body is touching the wall. Make sure that your ankle and shoulder are touching the wall. Now try to lift the foot that is on the opposite side of the wall. Can you lift your leg? No, you can't. Even if you can, you will fall to the floor and break some of your body parts.
If you want to know why you can stand like this, firstly, you have to understand the center of mass. In simple words, the center of mass is where all the mass of the body is concentrated. In other words, it's a place of a particle, where the sum of that particle's mass seems to appear. For balancing a system, the body must be balanced by the center of mass. For instance, if you want to balance a 30 centimetres uniform scale, you need to place your finger just at 15 centimetres' place: pretty much the center. Because that's where the center of mass exists for a uniform scale.
However, the center of mass does not always seem to appear at the center. When the mass is not uniform in all the places, the center of mass will tend to be concentrated on the most weighed side of that element. For example, the center of mass of a broom is placed near the bristles.
So, where is the center of mass of a human body placed? In a standing posture, it is pretty much around the navel. Therefore, when we stand flat-footed, we need to keep the naval point above the center of our feet. If we lean forward or backward, or sidewards, we need to balance our feet according to the posture.
Well! So when we are standing in a normal posture, our navel is aligned with the center of two feet. As a result, we can stand. However, when we lift one of our legs up then we need to put our other leg just below the center of mass point: navel to balance the total mass of our body. But when we try to stand by one leg with the ankle touching the wall, the center of mass is not aligned with the feet. It is slightly left or right (depend on which leg you have lifted). That's why we will fall to the other side because our body mass is not bolstered by anything.
Sometimes, we can observe that when a human lifts a suitcase or any heavy thing with the left hand that time he/she tend to lean to the right side slightly and vice-versa. This is because the man is trying to keep the center of mass just above the center of two feet. Otherwise, he will fall to the ground. This is the same reason why you can't do Michael Jackson's impossible, spine-defying dance move.
Physics is the only real science. The rest are just stamp collecting.-Ernest Rutherford
