Sound waves are mechanical waves. They can travel only through matter. They cannot travel through empty space. This was demonstrated in the 1600s by a scientist named Robert Boyle. Boyle placed a ticking clock in a sealed glass jar. The clock could be heard ticking through the air and glass of the jar. Then Boyle pumped the air out of the jar. The clock was still running, but the ticking could not be heard. Thats because the sound couldnt travel without air particles to transfer the sound energy. Is there any other place where sound cannot be heard? Here is a hint: is there any other place that does not have air molecules? Thats right, in space sound cannot be transferred. So can astronauts hear each other? Yes, they can, because they are in enclosed space stations or pressurized suits.In both cases, they are surrounded by air molecules. If they left their space ship and did not use their electronics, they would not be able to hear each other. Next time you watch a science fiction movie, think about this factoid. When spaceships are destroyed by hostile alien beings, there would be no sound heard. Sound waves can travel through many kinds of matter.

Question: "How do astronauts hear?"

Answer: "Via electronics."

Response: no

Mary loved walking through the woods with her dog, Max. Max and Mary would go on all sorts of adventures together. They really loved looking for blueberries together and then falling asleep next to each other in the tall grass. One day, as Mary was picking the blueberries, she turned around to find that Max was not there. She became worried and ran off to look for her dog. She looked in all of their favorite spots...next to the stream, in their secret hiding place behind the raspberry bushes, and even inside the old cabin that sat in the woods. But poor Max was nowhere to be found. Nonetheless, Mary would not give up. She kept looking and she found him not very far away. He had seen a squirrel and run to chase it. When Mary called Max's name he left the squirrel and happily returned to Mary, wagging his tail as he went.

Question: "Who was Max and with whom did he go with?"

Answer: "Max was Mary's dog and they would go together on adventures"

Response: yes

Magnets are able to place a force on certain materials. This force is called a magnetic force. The force a magnet exerts is a little different from the forces you may normally think about. You exert a force on a book when you lift it. You also exert a force on the pedals of your bicycle. In both those cases, those forces cause a change. The change you see in both these cases is called motion. Magnets, too, can produce change. They can produce motion just like you do. Unlike you, magnets do not have to touch something to exert a force. A magnetic force is exerted over a distance. Thats right, a magnet can push or pull certain items without ever touching them. Thats how the maglev train works. Do you know another type of force that does not require objects to touch? These forces are known as non-contact forces. Another type of non-contact force you may be familiar with is gravity. Gravity too can cause changes in motion. Gravity holds our moon in orbit without touching it.

Question: "How are magnetic forces different from other forces?"

Answer: "Magnetic force can produce motion without actual contact with certain materials"

Response: yes

Flowing water causes sediment to move. Flowing water can erode both rocks and soil. You have already learned that materials can dissolve in water. With enough time, even rocks can be dissolved by water. This process happens really slowly. It may take over a million years to dissolve a rock. It doesnt matter how big the rock is. With enough time, flowing water can dissolve it. Moving water also has the ability to move small pieces of rock and soil. How can water move a rock? Doesnt it need energy? Of course, water gets its energy because it is moving. Moving water has kinetic energy. Things that have more energy can do more work. When water stops moving it will have no energy. It will no longer be able to move the rock and soil. When this happens the rock and soil will settle to the bottom of the calm water. Scientists call this process deposition.

Question: "How long does it take for water to dissolve rocks?"

Answer: "It can take over a million years to dissolve a rock as the process happens very slowly"

Response:
yes