# B Mechanics of a throwing sling

1. Jul 22, 2017

### Riley Werling

Hey, im not sure if this should be posted somewhere else, if so if you could direct me it would be much appreciated. So my question is how would i find the rotational velocity of a sling and how i could use that to calculate the force of a projectile from said sling. Ive tried doing some research online but most of what ive read is way over my head so i was hoping someone here might be able to help me.

Thanks for any and all help you guys provide.

2. Jul 22, 2017

### Nidum

I assume that you are talking about a real sling - that is two thongs and a pouch which are whirled around until one of the thongs is released and the projectile flies free ?

The whirling speed is really determined by choice by the person using the sling . The speed picked up by the projectile is a simple function of the whirling speed and the effective length of the sling .

The effective length of the sling is the length of the thongs plus some additional length from your arms .

So how fast (rpm) can you whirl a sling and what is the effective length of your sling ?

Last edited: Jul 22, 2017
3. Jul 22, 2017

### Nidum

Hint : For simplicity you can assume that the centre of rotation for the whirling is at you shoulder . Remember that your arms will most likely be bent .

4. Jul 22, 2017

### Riley Werling

So how fast (rpm) can you whirl a sling and what is the effective length of your sling ?[/QUOTE]
Sling would be 48in long and idek what rpm would be.. cant find an average anywhere online socichave no clue

5. Jul 22, 2017

### Nidum

How fast can you whirl your arms around ?

6. Jul 22, 2017

### Riley Werling

Pretty fast, if youre asking for a number i couldnt tell you

7. Jul 22, 2017

### Nidum

Whirl you arm as fast as possible and count the number of rotations made in a minute or if you can't manage a complete minute try thirty seconds .

8. Jul 22, 2017

### Riley Werling

100

9. Jul 22, 2017

### Nidum

So 100 turns in 1 minute or 100 rpm . Good .

100/minute is 100/60 = 1.67 revs/second .

The speed of the sling pouch as it goes around in a circle is given by 2 * pi * L * (revs/second) where L is the effective length of the sling .

L= 48 inches but we'll convert that to metres for our calculations . So we'll use L = 1.2 metres .

Do you want to try working out the pouch speed ?

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