I suck at math. How many degrees per second should the hour hand on a clock rotate?

Coding Beginning Blender Code and Development
1

I suck at math. How many degrees per second should the hour hand on a clock rotate?

frame rate is 24 frames per second

86,400 frames per hour
1,440 frames per minute
24 frames per second

The seconds hand has to go around 360 degrees to count a minute

360/60 = 6 degrees per second for second hand

6/60 = 0.1 degrees per second for minute hand

… and now I have no idea what to do for the hour hand.

I fudged the numbers with geometry nodes and it looks like 0.008333 degrees per second works for the hour hand but I have no idea what I was supposed to calculate to get that number as the result.

2

you got it, just think of it in terms of how many seconds it takes to make a full rotation:
image

1 Like
3

I was watching a geometry nodes video (paused after the first minute and tried to do it myself before finishing the video) and the guy kept saying “this is 60 time slower than that and then 60 times slower than that and so on”. I took “60 times slower” to mean divide by 60 and it worked for the minute hand but not the hour hand.

So I did not actually “get it”. I was dividing degrees by 60 based on my bad interpretation of what the video said instead of doing something with seconds.

:frowning: and I’m staring at your chart and still not discerning what I was supposed to divide by what to get 0.00833

I’ll get back to this tomorrow. Spent an embarrassingly long amount of time on this. Was supposed to do something else 3 hours ago

4

Well, you find the seconds that it takes each hand to make one full rotation.

for the second hand, that’s easy, it takes 60 seconds to go around once.

the minute hand takes 60 minutes to go around once, so we multiply that by 60 (seconds per minute) to get 3600 seconds for the minute hand to do one full rotation.

The hour hand takes 12 hours to go around once, so multiply that 3600 seconds by 12 to get 43200 seconds to do one full rotation.

one full rotation = 360°

360° / 60 seconds = 6°/second [second hand]
360° / 3600 seconds = 0.1°/second [minute hand]
360° / 43200 seconds = 0.0083°/second [hour hand]

3 Likes
5

In short:
360 degrees (for a full circle).
Divide by 12 (it takes 12 hours for the hour hand to make a full rotation), gives 30 degrees/hour.
Divide by 60 (60 minutes in an hour), gives 0.5 degrees/minute.
Divide by 60 again (60 seconds in a minute), gives 0.0083 degrees/second.

In detail:
You may have been misled by the person in the video - The mistake is in thinking that because there are 60 minutes in an hour, the hour hand must move 60 times slower than the minute hand. In actual fact the hour hand is only 12 times slower.
In the time it takes the hour hand to do a full rotation (12 hours) the minute hand has done 12 full rotations.

By comparison, in the time it takes the minute hand to do 1 full rotation (60 minutes), the second hand has indeed done 60 full rotations. So that is why dividing by 60 worked for the minute hand but not for the hour hand.

Hopefully that makes some sort of sense.

1 Like