can someone please explain the slingshot effect in regards to a trebuchet (seige weapon)?

Question

How does the slingshot effect change the launch velocity of a projectile being fired from a trebuchet

Answer 1

I can't really explain it in physics terminology but I can explain it by analogy. And the best one I can think of is a cricketers bowling action.

Imagine there is one bowler whose arm is 1m long (a nice standard number to think about). And imagine that his arm rotates at a speed of 100km/h around that 1m radius that the end of his arm (ie the hand holding the ball) travels.

Now imagine a second bowler that has a (slightly less realistic) 2m long arm, and assume he also has an arm that rotates the same speed. That means that half way down his arm (his elbow) travels at 100km/h. Which means his hand needs to travel faster than that, otherwise his arm would bend backwards and snap off. I don't know if the exact maths is right, but his hand would have to travel at 200km/h to keep up with his 100km/h elbow. C = (pi)d, someone else can do the math.

Now imagine if the bowler had a flexible 1m long sling in his 2m long arm, with the ball nestled inside it. That now has to travel faster again to keep up, but the time it needs to travel that distance is even further reduced because the first few milliseconds of the delivery are in a state of relaxation (ie slack). The only way it can make up that time is to speed up just as the vertical momentum changes (ie at the top of the delivery action). Which means you have the ball, in the sling, trying to travel an average of 300km/h, but most of the speed in a short burst at the top of the delivery action (so the top speed would in fact be greater than 300km/h).

Replace the bowlers arm for the arm of the trebuchet, the sling for the bucket and the projectile for the ball, and you have your trebuchet.

Answer 2

Lets start with a ballista (Roman catapault). This works like a giant see-saw. There's a heavy weight at one end and the projectile at the other. The weight drops and the projectile accelerates. The weight hits the ground and stops, the projectile keeps going. The falling weight conveys velocity to the projectile, but the kinetic energy of the projectile is only it's weight times the square of it's launch velocity. Much of the energy of the falling weight is lost when it hits the ground.

A trebuchet is an improved version of the ballista. The projectile is carried in a sling. When the weight stops, a lot of its kinetic energy is transferred to the projectile by the whiplash effect. This means that both the velocity and energy of the projectile is much higher than for a similar sized ballista. It also explains why trebuchet arms tended to break more frequently than ballistas.

Answer 3

Can't give you a technical answer. But I saw a great program on tv about 2 years ago where they built a trebuchet and fired it a few times. Apparently they had wheels and as the sling started forward the wheels jerked forward as a result of the sling's movement. This caused a slingshot effect and added substantial distance and power to the whole process.

Answer 4

I am no expert but I would guess that having a sling makes the projectile travel faster at the point of release.

The sling would effectively act as an extention of the swinging arm meaning the projectile would be travelling faster than if it were attached directly to the arm. I am guessing this is the slingshot effect.

Answer 5

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