When you’re on a bus, corners can push you sideways. But what does it do to a balloon? Grab a balloon and get on board to learn a thing or two about inertia.
Make sure you keep hold of the string so the balloon doesn’t get in the driver’s way … or in the faces of other passengers!
What happens to the balloon when the bus accelerates?
You’re probably familiar with the feeling of a car, bus, or train speeding up. As the vehicle starts moving, an invisible force seems to push you back into your seat.
But if you have a helium balloon, it reacts in precisely the opposite way. It moves forward instead, against the acceleration!
One way to understand this strange observation involves Einstein’s ‘equivalence principle’. When he was working on his theory of relativity, Einstein concluded that if you closed your eyes there was no way to tell the difference between the tug of gravity and the tug you feel when you’re changing speed.
So when you’re on an accelerating bus, it’s like there is a small planet behind the car pulling you towards it. While it’s pulling you back into the seat, the air is also pulled back. Just as a helium balloon floats up to where the air is thinner in the sky, it floats ‘up’ to the front of the bus, where the air has thinned slightly.
Whenever the bus turns a corner, we can say it’s accelerating in a new direction. Keeping the equivalence principle in mind, this is why you get pushed to the side of your seat, and why the balloon floats in the opposite direction – acceleration is like gravity’s strange twin.
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23 March, 2018 at 8:03 pm
That was a good one!!!
24 March, 2018 at 10:18 am
This is fun to try!
22 April, 2019 at 8:34 am
That was awesome!