What tool should a scientist use to measure an object in milligrams

List one type of erosion and describe how it happens?

Avery hard rubber ball (m = 0.5 kg) is falling vertically at 4 m/s just before it bounces on the floor. the ball rebounds back at essentially the same speed. if the collision with the floor lasts 0.05 s, what is the average force exerted by the floor on the ball?

What is the earliest point in the universe that we can observe? why can’t we see back further than this?