# Haunted Pickup?

Hi there! I’m a bartender posting on behalf of my regular, Steve. Steve had a GMC Sierra pick up. When he placed a helium balloon in the passanger seat, the balloon leaned forward when accelerating, backwards when breaking. That’s backwards, what’s up with that? Steve said he would turn the air off completely and the windows rolled up. Can anyone explain these backwards physics?

Newton and Einstein have weekends off, but you might get some interesting ideas in the mean time.

We’re definitely interested in what everyone has to say! Thank you for letting us know they have weekends off.

It’s the same reason a helium balloon goes up when you release it, rather than like most stuff, which goes down. It’s lighter than air, so like anything lighter than something else, it moves toward the top; i.e. upward. A helium balloon moves backward – counterintuitively – when stopping b/c when braking the air mass inside the passenger compartment gets thrown & squished toward the front of the car, making the air near the front of the car more dense, which forces the balloon (being less dense) to the rear. The helium balloon always moves away from areas of more dense air. This is an experiment which is hard to do, but if you could measure the upward force on the same balloon, it would be more at sea level than in Denver, b/c the air is more dense at sea level.

I’m thinking this is something a person could make a little extra cash on in a bar bet … hmmm …

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And when you accelerate the balloon goes forward, and when you stop it goes backwards. I am not sure but always figured it was air acting like water. You accelerate the air moves to the back creating higher pressure so the balon moves to the front. Ready for more theories.

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I think we found our Einstein wasn’t out for the weekend after all, he just changed his name to @George_San_Jose1

This was a question in my freshman physics exercise book. @George_San_Jose1 has it right.

If you can be more specific regarding exactly what broke, we might be able to provide a good response. Was he in the act of braking when something was broken?

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It’s a common question when interviewing potential new hires for silicon valley high tech engineering jobs.

Then you can answer why are manhole covers round instead of square!

That used to be a common interview question too. But it isn’t used so much anymore for some reason.

One question that’s still used I think is : say you woke up one day and found you were the size of an ant. everything, all body parts, in proportion otherwise. other than being smaller, would you notice anything else unusual?

Think about what would happen if the balloon were outside the car.