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pneumoped
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Struck in head by rock!
This past Sunday I was rock climbing in Eldorado Canyon, Colorado. Another climber was on a route just left of me and well above me. When he climbed up onto the belay ledge he accidentally knocked loose several rocks. One rock hit me in the head. Fortunately, I was wearing my helmet and I was fine. The rock fell about 25 feet, it was about the size of a golf ball, and it was made of granite.
I want to express the impact that the falling rock had on my head. As a civil engineer in a field where I do not use much of my physics I had to spend some time refreshing myself with the basic equations.
Using the specific gravity of granite at about 2.6, I calculated its density at 162.24 lb/ft3 and then estimating the diameter of the rock at 1.25 inches, I calculated the mass of the rock to be about 44 grams.
I know that Force = mass * acceleration. And I know that acceleration due to gravity is 9.81 meters per second squared. So I calculated the force acting on the rock to be about 0.43 Newtons.
Based on anecdotal evidence and experience, I know that a 44 gram rock dropped on my head from a height of 1 inch is going to hurt a lot less than the same rock that fell 25 feet and hit me in the head. However, the force exerted on the rock is the same – 0.43 Newtons. And certainly the force exerted upon my head is different depending on how far the rock falls.
How do I express the force exerted upon my head? Certainly the velocity, mass, and distance are the key components in how hard the rock hits me.
Thank you in advance,
Chris
This past Sunday I was rock climbing in Eldorado Canyon, Colorado. Another climber was on a route just left of me and well above me. When he climbed up onto the belay ledge he accidentally knocked loose several rocks. One rock hit me in the head. Fortunately, I was wearing my helmet and I was fine. The rock fell about 25 feet, it was about the size of a golf ball, and it was made of granite.
I want to express the impact that the falling rock had on my head. As a civil engineer in a field where I do not use much of my physics I had to spend some time refreshing myself with the basic equations.
Using the specific gravity of granite at about 2.6, I calculated its density at 162.24 lb/ft3 and then estimating the diameter of the rock at 1.25 inches, I calculated the mass of the rock to be about 44 grams.
I know that Force = mass * acceleration. And I know that acceleration due to gravity is 9.81 meters per second squared. So I calculated the force acting on the rock to be about 0.43 Newtons.
Based on anecdotal evidence and experience, I know that a 44 gram rock dropped on my head from a height of 1 inch is going to hurt a lot less than the same rock that fell 25 feet and hit me in the head. However, the force exerted on the rock is the same – 0.43 Newtons. And certainly the force exerted upon my head is different depending on how far the rock falls.
How do I express the force exerted upon my head? Certainly the velocity, mass, and distance are the key components in how hard the rock hits me.
Thank you in advance,
Chris