Final answer:
The shape of the ripples formed when a pebble is dropped into a calm pond is circular. Multiple ripples occur due to the initial disturbance and reflections, and as they move outward, their amplitude decreases due to the energy spreading over a larger area.
Step-by-step explanation:
When a pebble is dropped into a calm pond, the shape of the ripples formed is circular. This is because the disturbance caused by the pebble spreads out uniformly from the point of impact. The concentric circles represent each wave front that is moving away from the source of the disturbance.
There are multiple ripples because the initial impact of the pebble creates a disturbance that spreads out and reflects off of the edges of the pond or other obstacles, thus creating additional circular waves. These waves move out, increasing in circumference as the radius of the circle increases. Due to the conservation of energy, the energy spreads over a larger area as they travel outward, resulting in a decrease in wave amplitude.