# Why does the initial bounce distance (from origin of release) for a ball increase with mass of the ball?

I have completed an experiment on the effects of the wetness of a ball on its trajectory when projected. What the data I collected says that the more wet a ball is (determined by the mass of the ball after wetting), the farther away its first splotch/bounce will be from where it was released.

Here is an image of our launching mechanism AKA catapult:

How the mechanism works is that we put the ball into it (it's gripped by the tyres at the bottom) and then we let go of the string shown, from a controlled height. The mechanism then swings and hits a ruler, which causes the ball to jolt out of the tyre grip, launching through the air.

We then measure the distance from where it was released using a tape measure.

BTW distance is in metres. This shows that there is a positive correlation between both.

However, we were expecting quite the opposite:

We know from conservation of energy that all the balls should have the same initial velocity upon release from our catapult mechanism, because $$v= \sqrt(2gh)$$. Since we assume this, we know that all the balls have the same initial velocity upon release. After release, the only force (in an ideal world) acting on the ball is gravity/weight force. Thus the downwards acceleration of all the balls should be around $$9.8 m/s^2$$. This means that all the balls should land at exactly the same spot, and so make identical splotches.

What then is causing this difference in splotch distance? Could someone provide some insight, if not an answer, at least a point in the right direction.

• Which part of your trebuchet is providing the elastic potential energy? – harshit54 Oct 20 '18 at 4:53
• What is the ball made of? – Farcher Oct 20 '18 at 5:51
• @Farcher it's a standard tennis ball – Jainil Shah Oct 20 '18 at 6:49
• @harshit54 it gives the ball gravitational potential energy, which is converted to kinetic as it swings down. – Jainil Shah Oct 20 '18 at 6:50
• Where does the energy come from? You pull the string and then where does the energy get stored? – harshit54 Oct 20 '18 at 7:01