Timeline for The falling broom handle
Current License: CC BY-SA 4.0
17 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Oct 23, 2019 at 4:54 | comment | added | JiK | This answer is incorrect. There are other vertical forces than gravity acting on the broom. Namely, the support force from the floor on the head of the broom. Therefore, the total acceleration of he centre-of-mass is not $g$. | |
| Oct 23, 2019 at 4:54 | comment | added | xnor | @Conifers I just posted an answer, take a look. | |
| Oct 23, 2019 at 4:52 | comment | added | Conifers | @xnor if the cup could catch ball, then means cup falls faster. If not, that means ball should fall faster, however the rod is under the ball, so it might be they will accelerate commonly when angle is above 35.3(ball falls faster, and give the rod a normal force). Then if begin to below 35.3, they might motion seperately(bacause rod now falls faster than ball.) Anyway, I'm not major in Physics, need someone pro to validate :( | |
| Oct 23, 2019 at 3:32 | comment | added | xnor | @Conifers See my comment above, the 35.3 degrees isn't the right cutoff for this problem. I'm still not sure what they mean about the cup catching the ball, but the equation they solve is definitely just setting their initial accelerations equal at the starting angle. | |
| Oct 23, 2019 at 1:03 | comment | added | Conifers | Typo, not vice versa, should be slower when angle less than 35.3. | |
| Oct 23, 2019 at 0:57 | comment | added | Conifers | @WeatherVane Yes, the linked problem should be maximum, and if the cup could catch ball, means the end of rod will fallen to ground faster then the ball, which seems equal to this puzzle's asking(rod->broom, ball->keys). So the answer is neither all of 3 options and should be the fourth: It depends on the brooms angle, key is faster when angle more than 35.3 and vise versa. | |
| Oct 22, 2019 at 22:56 | comment | added | xnor | I don't see how the linked problem demonstrates the angle at which both hit the floor at the same time. Their formula is finding the starting angle at which the initial angle of the end of the rod has the same downward acceleration as the ball (key). But, we want to know which one hits the ground first, which involves the acceleration over their whole paths. Presumably the equalizing angle is greater than 35.3°, so that the ball accelerates faster for the first part and slower for the rest. | |
| Oct 22, 2019 at 17:40 | comment | added | Weather Vane | @Conifers page 2 of your linked example says the critical angle is 35.3° and although it says minimum angle I think it should say maximum angle as the broom plainly lands last when nearly vertical. | |
| Oct 22, 2019 at 17:28 | comment | added | Jeffrey | This is incorrect. It depends on the broom angle. It is only true for broom close to the ground (low angle). If the broom was up at a angle of 89 degrees, visibly, the key would hit first. | |
| Oct 22, 2019 at 16:44 | comment | added | Conifers | Maybe is it the answer? dev.physicslab.org/… | |
| Oct 22, 2019 at 16:16 | comment | added | Weather Vane | So do you agree that there must be some starting angle when they both hit the ground at the same time? | |
| Oct 22, 2019 at 15:39 | comment | added | AndyT | @WeatherVane - I've now done a quick test with a short (15cm / 6in) ruler and a pen. I agree that when the broom/ruler is nearly vertical it lands a lot later. When the angle is below 45 degrees... it's all too fast for me to judge. Hmmmmm! | |
| Oct 22, 2019 at 15:32 | comment | added | Weather Vane | I have tried it. When the broom is nearly vertical, it hits the ground a long time later. From an angle of about 60° to the horizontal, the broom still lands noticeably later. At lower angles I am unable to determine as they seem to land at the same time. If this answer (broom lands first) is correct, there must be a particular starting angle when they take the same time. | |
| Oct 22, 2019 at 13:57 | comment | added | AndyT | Chalk one up for the Chartered Engineer getting a physics question right. Phew! | |
| Oct 22, 2019 at 13:54 | comment | added | Jaap Scherphuis | You have good instincts, as this is the correct answer. The difference in speed is quite noticeable, and I highly recommend people try it out for real and see for themselves. A small amount of energy is taken up by the rotation of the broom, and if there is friction by the sideways movement of the broom, but at the kind of angle shown in the question those are small enough to make very little difference. | |
| Oct 22, 2019 at 13:53 | vote | accept | Jaap Scherphuis | ||
| Oct 22, 2019 at 10:17 | history | answered | AndyT | CC BY-SA 4.0 |