Skip to 0 minutes and 10 secondsGravity can be a help or a hindrance. Either way, it must be incorporated into our free-body diagrams. If we are talking particles, we need only know the magnitude of the force that gravity produces. When we are talking rigid bodies, we need to know where a gravity force acts, because where it acts determines the twisting effect - as seen in our free-body diagrams - and these determine the distribution of forces. For shapes like squares or spheres or cubes, we can see that the centre of gravity is in the geometric centre. But what of more complicated shapes? Splitting up a composite shape into simple elements gives us a way of finding its centre of gravity. A table can be a big help.
Skip to 1 minute and 5 secondsWe saw the importance of load distribution - and hence, location of centre of gravity - in aircraft, not that it bothered conceptual artist, Panamarenko, beside his flying wing in SMAK, the Municipal Museum of Contemporary Art in Ghent, in Belgium. The description read, "Panamarenko started building Utopian aircraft in the 1960s. His quest for air-worthy constructions never resulted in functional machines." The possibility of failure is an inseparable part of his work, and gives it its poetic eloquence - so different from engineers' eyes. Gravity is the most basic of loads. The next load we'll consider is friction.
Through Engineers' Eyes
This quick video highlights your progress towards Engineers Eyes. The concept wheel shows how it all fits together.
Week 1 concept wheel (Click to expand)
This week you found where gravity forces act so you could show them properly on FBDs.
It was an example of equivalent force systems. Gravity acts on all the particles of a body, but we generally need to represent this by a single force (weight) at a special point (the centre of gravity).
You saw two ways of finding centres of gravity by experiment (or perhaps you did the experiments yourself), but how can we find them by calculation? The answer is to use the method of composite bodies (preferably with a table or spreadsheet).
Oh yes. You also learnt about two-force objects: a neat trick that can simplify many an analysis.
These are to get you started. Share any other thoughts you’ve had.
- From the video, according to S.M.A.K. (the Municipal Museum of Contemporary Art in Ghent, in Belgium), the conceptual artist Panamarenko “… started building utopian aircraft in the 1960s…His quest for air-worthy constructions never resulted in functional machines. The possibility of failure is an inseparable part of his work, and gives it its poetic eloquence”. Does this have anything to say about engineers’ eyes?
Share your experiments
Don’t forget to share your experiments on the Through Engineers’ Eyes Padlet wall for this week.