Jearl Walker www.flyingcircusofphysics.com
August 2014 One of the common myths (I guess it would be a rural myth instead of an urban myth) is that you can tip over a cow while it is standing and sleeping. I have no idea why anyone would even entertain hurting such a valuable and lovable animal like that, but let’s consider the physics alone. Is it possible for a person to push sideways on a cow’s rib cage so that the cow tips over and onto the ground?
Here is Sheldon arguing that physics will not allow such a thing (the link to the video clip is at the bottom of this story).
First of all, if the cow is standing, it is awake, not sleeping. As explained in this video link here, a cow cannot stand while sleeping like a horse because its knees do not lock in place like those of a horse. A cow might be standing quietly but it is contemplating its existence, not sleeping.
Given that the cow is awake, if you push on cow, it will merely step away from you, either forward or to the side. However, suppose that the cow is arrogant and chooses to ignore you, figuring that you are pushing on it because you have nothing better to do after spending the day in a pub. Even if the cow does not move out of the way, your force is too weak. You are trying to rotate the body around a ground-level axis through the hooves on the opposite side of the cow. Here is a sketch in which a force attempts such a rotation in the counterclockwise direction. In physics jargon, you are applying a positive torque to get a positive rotation.
However, opposing your torque is a negative torque (clockwise) around the rotation axis due to the gravitational force on the cow. That force is said to act at the center of mass of the cow. Because the cow’s weight is very large, that opposing torque would be much greater than your torque, and thus the cow will just turn its head and smirk, with a look that suggests you should return to the pub.
To see a calculation with fairly realistic numbers use this link:
How about if several people attempt to tip over cow? The combined force then might indeed produce a torque to overcome the gravitational torque. However, you still have to convince the cow remain stationary instead of just stepping aside and watching everyone fall facedown onto the ground (and whatever the cow has already left there).
I think the only way a cow could possibly be tipped is if several people run at the cow with arms outstretched and hit the cow simultaneously. But I think the cow would then be injured (broken ribs, perhaps on both sides of the body). However, only very fast runners could pull this off. Not only would they need to run fast at the cow, but then they would need to run fast away from the shotgun blasts from the rancher.
https://www.youtube.com/watch?v=3RVmHYboT8o The Big Bang Theory: Sheldon claims that Penny’s tale of cow tipping is fictitious
https://www.youtube.com/watch?v=-VAkjXUBmZU morning show
http://www.npr.org/templates/story/story.php?storyId=219963377 National Public Radio interview
If you would a list of the links to all the pub tricks I have posted, go here and then scroll down to "Pub physics".