All physical actions requiring touch are physical karma. Physical karma leaves behind physical residue. Let us say you have an apple. You peel and deseed it to enjoy better taste. You eat the apple leaving the skin and seeds behind. Your action of eating the fruit has resulted in the residue of apple skin and seeds. You dispose of the uneaten parts. A cow comes and gladly accepts that as its food. The residue you left behind has now impacted someone else you may not even know. That apple you consumed is now in your body. It is processed by your digestive system. Two sets of residue are formed. The one that gets absorbed in your body is now travelling in your veins by way of blood and the unabsorbed portion is let out of the your physical system by the way of urine and faeces. Further, bacteria and other microorganisms may feed on such excreta.
Your physical karma of eating an apple has left an imprint on you and other lifeforms. The residue from the apple that is in your blood directly affects your physical health. The residue eaten by the cow has a bearing on its health and on the quality of milk it produces. The excrements from your body have an impact on micro organic life forms as well as the environment.
Now imagine seven billion humans on the planet doing that. Further envision billions of other living creatures in the equation. The physical world is a residue of the collective karma. It is the residue that matters. Your physical karma has a telling impact on your and your immediate environment. Plus, it has an impact on the whole world. It is for this reason that the path of meditation requires a degree of self discipline and restraint. No matter how minuscule an action, eventually it will impact everyone in the world.
Reference : A Million Thoughts. Om Swami.