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Will a soccer ball bounce more times on natural soccer field style cut grass or artificial turf? In our experiment, natural grass had more bounces. That surprised us. Why would natural grass be bouncier? I can't find anything explaining why that happened scientifically. There is tons of info on why balls bounce and the physics behind it, but no info on why the bounce is different. We thought artificial grass would bounce more because of the rubber. I am thinking the natural grass surface is harder so that would make the ball bounce more, but not sure how to explain that scientifically.
Question Date: 2016-01-12
Answer 1:

Sounds like an interesting research problem. Like for many problems, there is a lot of information you can draw from, but it's difficult to figure out how to apply it. I still think it's worth trying! Here's my attempt.

A useful way to think about this problem is in terms of elasticity of the collision between the ball and the ground. In a perfectly elastic collision, the ball collides with the ground and bounces off with as much momentum as possible. In this kind of collision, the ball loses no energy, so no sound is made and no heat is generated. If you let the ball continue to bounce in a perfectly elastic way, it will never stop bouncing. (This is not practical: any collision I know how to set up is not perfectly elastic.)

The opposite situation is a perfectly inelastic collision. In this case, the ball collides with the ground and loses all of its momentum and all of its kinetic energy. All of that energy is converted into heat or sound--usually both. Imagine dropping a cannonball on the grass: you end up with zero bounces and a lot of noise.

You found that the collision between the soccer ball and natural grass field is more elastic than the collision between the soccer ball and turf field. Why? The difference must come from the ground surface, so let's think about what factors can affect elasticity. Maybe the dirt below the natural grass plays a role, or the under layer below the turf (often rubble or gravel). We could test how many times a soccer ball bounces on similar dirt or similar gravel and see if that lines up with the grass surfaces. I would also consider the arrangement and texture of the grass. Think about how corrugated cardboard is stronger than flat sheets. The way that the grass weaves together (or doesn't weave together) might affect the elasticity.

Answer 2:

The difference in the bounce is because of the properties of the grass/turf that absorb the kinetic energy of the bounce and turn it into heat. The natural grass is probably less rigid and so absorbs less energy before the ball hits the dirt and bounces. You could do an experiment in which you bounce the ball on dirt with the grass removed and see how much the presence of grass affects it.

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