bureau44 t1_je80tqt wrote on March 30, 2023 at 1:59 AM

This one is pretty trivial. The result will be the same be it plane, train or a boat.

A little bit trickier puzzle: What would happen if I had a big enough airplane to fly a small helicopter or a drone inside. Will the plane become lighter?

Quietm02 t1_je8rn59 wrote on March 30, 2023 at 6:20 AM

Imma say no.

Helicopter works by pushing air down. That air hits the floor of the plane, giving the same "weight" as the helicopter just sitting there anyway.

A real interesting question is what happens if I have a big train going half the speed of light. Then stick another train on top going half the speed of light. Does the second train go at the speed of light?

bureau44 t1_je9a0l2 wrote on March 30, 2023 at 10:40 AM

Sure it won't.

As with speed of light the answer is also no even if you put a third train on top of the second. But I fear I am not able to eli5 this.

Quietm02 t1_je9e5e7 wrote on March 30, 2023 at 11:27 AM

You're right it won't. The short answer is that adding velocity together is an approximation that only works for low speeds. It doesn't work when you get near the speed of light.

This link explains better than I can https://galileo.phys.virginia.edu/classes/252/adding_vels.html

Animal_Soul_ t1_je8qcge wrote on March 30, 2023 at 6:03 AM

Check out Mythbusters. They did a show with pigeons and a model helicopter in a truck to test whether the truck became lighter when things inside the truck were in flight.

They tested the pigeons and the helicopter separately otherwise things might have got a bit messy.

bureau44 t1_je99ozz wrote on March 30, 2023 at 10:36 AM

I know the answer. I just thought it is a bit more fun question.

But apparently some people here struggle even with the OP's original question from middle school. Newton's first law. Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.