4.1

Skip to 0 minutes and 10 secondsImagine you're the pilot of this aircraft. As one of your pre-flight checks, you're going to see if the centre of gravity of the loaded plane is within specification. Why? You can see for yourself using those paper gliders. Try the yellow one. Launch it gently.

Skip to 0 minutes and 34 secondsOh dear. Its centre of gravity is too far back. It stalls and crashes. Try the blue one. Good. That one has a ballast mass on the nose, to bring the centre of gravity forward under the wing. You can trim a paper aeroplane by trial and error, but not a real plane-- you have to calculate it. That's what you'll do for the paper glider in this week's design task. But first, we'll do some experiments. We'll use two measurement methods to find the centres of gravity of some basic shapes, and some combinations of shapes. The analysis will show you how to find centres of gravity by calculation. Then you'll be ready to decide on the ballast for the paper aeroplane.

Centre of gravity

Engineers often defy gravity. Think of bridges, aeroplanes, or houses. Even washing lines (seen in Week 3).

To understand their tasks they need to know the magnitude of the gravity force, and where it acts. That is, they need to know weight and centre of gravity.

It’s not only used in Statics. For example, in Dynamics, when dealing with accelerations engineers need to know the related concepts of mass and centre of mass. But that’s another story.

This video sets the scene and explains how to calculate the weight of an object from its mass.

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This video is from the free online course:

Through Engineers' Eyes: Engineering Mechanics by Experiment, Analysis and Design

UNSW Sydney