A bear scratches his claws on a big pine tree. Does the bear do work on the tree? why or why not? (btw it has to do with physics) ITS NOT A GENERAL QUESTION.

Which describe reflection? check all that apply. light bounces off a boundary.

In which situation has the independent variable for the experiment been changed? check all that apply. changed from counting the number of duckweed at day 0 and day 14 to counting them every day changed from testing duckweed growth in beakers to testing duckweed growth in large outdoor tanks changed from testing the effect of ph on duckweed growth to testing the effect of light levels on duckweed growth changed from testing the effect of acid ph on duckweed growth to testing the effect of basic ph on duckweed growth

Mixing salt in water is an example of physical change