Remember that the centre of mass means the single point where the mass of a spread out object seems to act.
To do this experiment, I used my protractor to make a big angle measurer. You can make your own if you like. You could choose to print it or just display it on a screen to help you measure an angle.
You need an empty bottle WITH A LID ON. The centre of mass of all of that plastic will actually be in the centre - marked with an X on the photo. Stand the bottle in front of the angle measurer, lined up with the vertical line.
Then lean the bottle over to the side. If the angle is very small, then the bottle won't fall over. It will wobble but then go back vertical. What I want you to write down is roughly the angle at which it won't go back vertical and actually falls over. It won't be very accurate. Try best of 3!
I also tried the water bottle below. It has a wider base which might give better results.
Now fill the bottle roughly to a quarter full with water. PUT THE LID BACK ON SECURELY - don't let it spill water when it tips.
The water is much heavier than the plastic so now the centre of mass moves down to the middle of the water. So if the water goes 1/4 of the way up the bottle, the centre of mass is half that or 1/8 of the way up the bottle. Find out the angle of lean for which it first falls over.
Repeat with the bottle
1. Half full.
2. Three-quarters full of water.
3. Totally full of water.
SCREW THE LID ON TIGHT EACH TIME!
