Question

Have you ever noticed that whenever you lift something heavy with one hand and walk, your head(actually your whole body) tilts a little to the side opposite to the hand carrying the weight? I have thought about this for months, and now with the tools of rotational mechanics, I think I can finally analyze this.
First of all why do you think this happens? I have always thought of this occuring to attain balance of the body. But I am seeking an explanation with rotational mechanics.
Next, if we have figured out why this happens, can we physically analyze the situation?

Answer 1

For example, If a lift of weight W with my one hand, can we calculate to what angle will my head(body) tilt to the other side?
This is my personal experience with the world, so if I have been unable to explain my problem to you properly, please say so.

Answer 2

when we lift a weight our centre of gravity shifts towards the hand carrying the weight........... so we move the other hand to bring back the centre of gravity back to its place.............

This is what i know. i will think about the rotational mechanics........

Answer 3

That's a good reason. Thanks.

Answer 4

We want our center of mass (center of gravity, ...), CM, to lie on the vertical axis of our body. To the extent that the CM does not lie on that axis, but is a distance r away in a horizontal plane, it creates a torque of magnitude
\[ | \tau | = r (CM.g) \]
and as \( \tau = I\alpha \), this non-zero torque tries to accelerate our body to rotate and fall.

That's why we adjust our bodies--to try and minimize the torque that the mass is inducing.

Answer 5

To adjust our bodies, we need to create another opposing torque. Where does that come from?

Answer 6

From contracting muscles on the opposite side of the body, contracting them, making the skeleton and the rest of the body move towards them.

Answer 7

From contracting muscles on the opposite side of the body, making the skeleton and the rest of the body move towards them.

Answer 8

An internal force! That's a problem. Just one last question, if I have a weight W, will be it be possible to calculate the angle through which the body tilts?

Answer 9

It depends on how far away the weight is from your body and the height at which it is held, as well as the distribution of mass in your body. You can make simplifying assumptions, such as considering your body to be a uniformly dense cylinder.

Answer 10

Thank you! I will really try this.

Answer 11

there is also the diferance in the forses you apllay to the ground with your feets.

Answer 12

@mos1635, yes probably there is. You press the ground with more force due to one foot than the other. That's what creates the torque, and causes the tilting.