Okay, so I had a really weird dream last night which I could turn into a pretty neat little horror story.
However, one of the main plot points of this dream involved a bowling ball being thrown down a flight of stairs, and as the ball bounced down the stairs, it shook the ramshackle house enough that a rocking chair in the attic began to rock.
As I took my morning shower, it occurred to me that since a bowling ball is only about 40 pounds in weight, for the force of it bouncing down the stairs to do so much, the general movement of the people in the house would be enough to do so as well, which kind of negates the whole thing.
So could a bowling ball falling down the stairs shake a house more than regular movement by the people in the house? Or do I need to go back to sleep and come up with a better plot device?
Perhaps along the lines of resonance. The only problem I think (trying very hard not to draw pictures of bowling balls and steps), is that the horizontal velocity of the bowling ball would increase as in descends the steps, so the impulse from the vertical drop of the ball would not be periodic, rather the frequency will increase for each step. At some point the horizontal velocity will exceed L/sqrt(2H/g), where L is the tread length, H is the step rise, and g is the gavitational constant(Damn I was close to drawing something there). At that point the ball will glance off the step’s arris and do unpredictable (by me) things.
So if the old rocker as some sort a arrangement where is resonates with the aperiodic thumping of a bowling ball, sure it will work.
What you could have, is a shelf in the attic with a bunch of 8lb* bocce balls on it. The thumping upset then, and they roll off onto some part of the rocking chair, driving it.
I know 8lb bocce balls would also me known as shot puts, but I couldn’t resist.
Well, yeah, a 16 lb bowling ball could make a heck of a thud, provided it was dropped from a height large enough to let it build up some momentum. Remember, most people don’t get up a lot velocity when they walk down stairs. In fact, they use their muscles to decelerate. Even if you jump, unless you keep your limbs locked, you’re going to absorb a lot of the force by bending and distributing the impact over a longer time.
Think about it this way. I could take a six or eight pound sledge hammer and give your staircase a whack that would wake the neighbors.
The real problem is that the vibration generated by the pounding is unlikely to make a rocking chair rock. That would require an impulse against the back of the chair parallel to the floor, or perpendicular to the floor against the seat but at a distance from the chair’s center of gravity. So you’d have to rely on the vibration knocking something onto the chair, have it dislodge a chock from under one of the chair’s runners, or have it startle one of the denizens of the attic (raccoons or squirrels) and have them start the chair rocking.
Way back when I studied such things, I was in a lab class that was studying impact. The idea behind the experiment was to see what difference the surface impacted made to the object falling. To make it more interesting, we considered the accelerations a human head would feel if someone fell and hit is head. The object we used to approximate a human head was a bowling ball. The professor suggested that a bowling ball wasn’t an unusual stand-in.
So, what I’m suggesting is that you are right, a bowling ball isn’t going to make a great deal difference more than people walking around. Maybe if you drop a person down the stairs…
I may be dense today, but aren’t the horizontal and vertical velocities independent? The vertical velocity increases if it were allowed to freefall, but the horizontal velocity should stay at the initial one given to the ball, or even decrease due to friction.
As the ball rolls over the edge of the step, it rolls over and forward, collecting angular momentum as well as horizontal velocity. Even without friction, the ball would slid forward over the edge.
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The crude drawing shows a bowling ball partly rolled off the step. It is intuitively obvious that the ball will move to the right so-as to continue down.
For a plot solution…
My uncle has a beach house (on stilts - pole construction) and whenever his Lab (dog) walks from one end to the other it rocks the rocker.
