Center of gravity

Looks like Philip didn't hit the brakes in time. Or did he? Half of the car is still on the cliff. So will the car fall off? If more of the car's weight is in this half then the car will fall.

And if more of the car's weight is in this half then the car won't fall. The centre of gravity is a point where we imagine that the total weight of an object is located. The position of the car's centre of gravity depends on how its mass is distributed. The heavier the car is on one side compared to the other, the closer the car's centre of gravity will be to that side. All objects have a centre of gravity.

The centre of gravity helps us figure out how easy it is tip something over. Look at this box. How far do you have to push it to tip it over? Here is its centre of gravity. The area it stands on is called the supporting base.

Look what happens when we try to tip the box over. As long as the centre of gravity is still within the supporting base it doesn't tip over. But when the centre of gravity is outside of the supporting base, the box tips over. And that's the box's tipping point. Now look at this box.

It's heavier at the bottom than the other box. This means that its centre of gravity is lower. It also has a larger base. You have to push it much further before it tips over. Let's flip the box over.

See how the centre of gravity is now much higher than before? And the base is smaller too. It's much easier to tip over! Things like cars are built with a low centre of gravity and a large supporting base, so they don't tip over easily when they turn or brake. Of course, Philip's car is on the edge of a cliff so its supporting base is only half of what it normally is.

The car's centre of gravity is here. Looks like it's going to fall... ... but Kim and Philip think fast and rush to the back of the car. Now the back of the car is heavier so the centre of gravity shifts a little bit to that side. Just enough for them to escape...

out of the back door. But without their weight, the car's centre of gravity is outside its supporting base again. It's past its tipping point. Time to say goodbye to the car. Now it's in the hands of gravity.