Effects of Earth's spin on projectile motion. (1 Viewer)

[fr3d]

I've been eating through my school's past papers, I found this question:

"Explain how the Earth's rotational motion (sic) would influence the aiming of the cannon in order to hit a target which is geographically due north of it"

I answered that it wouldn't affect it at all, because the target and cannon aren't moving, relative to each other (because they are both moving with the spin of the Earth).

The answers say:

"The velocity of the Earth's surface is greater at the equator. Thus as a shell is fired N it also gains this lateral velocity. As it travels N it moves East of its target as the velocity of the Earth's surface is less, further North."

Is this correct? (it must be, but... still, it doesn't seem intuitive)

(BTW, this was part B of a three part question, in part a, we calculated that the horizontal velocity was 199m/s.)

Thanks,

Fred.

 

[someth1ng]

Yeah, it's right but I do agree that it's counter-intuitive - I also thought it had no effect but when I read the answer, it made sense.

Also, this question was designed to catch the rote learners because when Galileo did the tests, he found that a ball dropped was already following the motion of the Earth but it really makes you think when the cannon ball moves North/South.

 

[fr3d]

Thanks,

I guess I'l have to stop and think for a bit when I see questions like these.

F.

 

[SnowFox]

Iirc its call the coriolis effect.

 

[someth1ng]

Iirc its call the coriolis effect.

Yeah, just had a look - you are right.

@OP, it's rare, if ever, do they ask to explain something that is not true.

Keep that in mind.