An blank is an object that allows only some electrons to go through it

What evidence supports the theory that there is a black hole at the center of our galaxy?

Why do scientists use Punnettsquares? (Site 1)

A railroad car of mass m is moving at speed v when it collides with a second railroad car of mass m which is at rest. the two cars lock together instantaneously and move along the track. what is the speed of the cars immediately after the collision?

Blood pressure is measured when the blood is pumping (systolic) and when the heart is resting (diastolic). When pressure readings are given, the systolic is given first, and healthy blood pressure is around 120 over 80 mm Hg.

You push a wall with a force of 50 N. If the wall doesn't move, what is the net force on you? p. s. I'm pretty sure it's either 50 or 100 but I'm not quite sure

Design an experiment (Fair Test) to find out what would be a good insulator for a dog house.

Which of these changes does a submarine encounter as it returns from the bottom of the ocean to the surface of the ocean? a. the amount of sunlight increases. b. the water temperature decreases. c. the amount of plants decreases. d.

Why do some elements have symbols that don't use letters in the element's name?

How many (whole number of) 91 kg people can safely occupy an elevator that can hold a maximum mass of exactly 1 metric ton? A metric ton is 1.000 * 103 kg. Answer in units of people.

What are the two types of surface waves? How are they different and which one would cause more damage? Explain.