Hi,


I recently read a book called "Evolution and Beyond, Why We Are More than Evolving Chemicals" on kindle.

One of the arguments that the author makes is that we have the ability to self-move. This I can’t deny this because there is nothing pushing me or pulling me around. I move myself around. The problem is, as he points out, that Newton's laws of motion (the only physics of motion) only allows for movement that is due to the application of an outside force. Meaning that an object can only move if it is pushed or pulled in a certain direction. There is no provision in Newton's laws of motion to allow an object to generate its own forces to cause its own movement. My question is, how is it possible for us to self-move if Newton's laws of motion does not allow for self-movement to occur?


Thanks.

I think there's a misreading/simplification of newton's laws here...  a car would similarly fall into the category of self moving, as would of course pretty much all other animals.

At a basic level, you could consider that your torso is being pulled/pushed by your legs. Your legs are incorporating gravity to pull you. Muscles pull against bone, and the skeleton transmits that force to the ground (or other substrate).

If you were in a gravity-less vacuum (i.e. in space and unsupported) you would be unable to move (beyond fruitlessly waggling your arms and legs).

we "self-move" because every cell in our body has mitochondria which generate energy (effectively a power cell). As Peter says it is no different to any engine.

Also, there really is an outside force pushing you around when you walk; two forces in fact: gravity and friction. Walking just amounts to pushing backwards against the ground with your feet. When you do this, the ground then applies a forward force against your feet in the form of friction. The foward force is equal and opposite to the backward force that you apply. (Newton's 3rd law) so it does not actually move you forward, but it keeps your foot from sliding backwards. This makes your leg pivot forward and then gravity pulls the rest of your body forward. You then place your other foot on the ground to counteract gravity and stop yourself from falling on your face. This is why it is hard to walk on a slippery floor or on ice. The lack of friction means that there is less of a forward force being applied when you try to push backwards with your foot.