pendulum in spacecraft EK physics in-class exam

[Jwinsler7]

Instead of writing an entire passage, I will paraphrase here.

A spacecraft is orbiting an unknown planet, and a pendulum is in the space craft. A real pendulum on the clock in orbit would:

A. Swing more slowly than it would if it were on the planet below.
B. Swing more swiftly than it would if it were on the planet below.
C. Swing at the same rate as if it would on the planet below.
D. Not swing on the orbiting spacecraft.

My guess was A because I thought the effect of gravity would be slower as you go further away from a planet. But the correct answer is D. EK explanation is "Since the clock is in free fall(??) the entire apparatus is propelled by gravity and pendulum would not fall faster than the apparatus from which it is hanging."

I am having a hard time understanding what the explanation means. Help?
Thanks in advance

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[rickrun]

Well, keep in mind that a pendulum on Earth swings because gravity is acting on it, but also because the apparatus the pendulum is attached to is keeping it from falling to the ground. This is because the apparatus is basically pulling the pendulum upwards against gravity. So, the pendulum swings.

In free fall, the pendulum AND the apparatus are in free fall, which means they are both being pulled down together. There nothing is pulling up on the pendulum, and its no different than if you were to hold a pendulum in your hand while you were in space, and then dropped it. It wouldn't swing, it would just fall towards the Earth.

 

[sciencebooks]

Well, keep in mind that a pendulum on Earth swings because gravity is acting on it, but also because the apparatus the pendulum is attached to is keeping it from falling to the ground. This is because the apparatus is basically pulling the pendulum upwards against gravity. So, the pendulum swings.

In free fall, the pendulum AND the apparatus are in free fall, which means they are both being pulled down together. There nothing is pulling up on the pendulum, and its no different than if you were to hold a pendulum in your hand while you were in space, and then dropped it. It wouldn't swing, it would just fall towards the Earth.

It's such a lame thing to lose points on but I always forget to treat orbit as free fall... Even though it is, .

 

[Jwinsler7]

Thank you guys!

 

[ELTURC0]

Thank you, this helped

 

[Grad_2011]

Could you also look at this question in the sense that, because there is no gravity in orbit, then acceleration would be zero, so F = ma would also be zero? Because that may have been how I thought of it originally... Maybe.