QUES: Take a look at this train in Figure 1.11. It looks very futuristic. What do you notice about it? Did you notice that the train has no wheels? How can a train have no wheels? It doesn't need wheels. It actually floats, or levitates, just above the track. Magnets enable the train to do this. This is not a normal train. This is a maglev train. The word maglev stands for magnetic levitation. Because it has no wheels, there is no friction. Some magnets hold the train up. Other magnets are used to move the train forward. This train can go very fast. It can reach speeds up to 480 kilometers (300 miles) per hour! Magnets are pretty cool. What exactly is a magnet? How is it able to exert such force?
Do you have any questions?
MY QUESTION: What holds the train up and moves it forward?

QUES: You might want to know how cold it is. You may need to know how fast the wind is blowing. Maybe it rained last night? Do you know how much? Does it feel humid to you? You have heard all these questions before. To answer these questions, we need data. That data comes from special tools. These tools collect data about the weather. You can see some of the common tools listed below: A thermometer measures temperature. An anemometer measures wind speed. A rain gauge measures the amount of rain. A hygrometer measures humidity. A wind vane shows wind direction. A snow gauge measures the amount of snow.
Do you have any questions?
MY QUESTION: What question does a thermometer answer?

QUES: From Babylon, Alexander went to Susa, one of the Achaemenid capitals, and captured its legendary treasury. He sent the bulk of his army to the Persian ceremonial capital of Persepolis via the Royal Road. Alexander himself took selected troops on the direct route to the city. He had to storm the pass of the Persian Gates (in the modern Zagros Mountains) which had been blocked by a Persian army under Ariobarzanes and then hurried to Persepolis before its garrison could loot the treasury. On entering Persepolis, Alexander allowed his troops to loot the city for several days. Alexander stayed in Persepolis for five months. During his stay a fire broke out in the eastern palace of Xerxes and spread to the rest of the city. Possible causes include a drunken accident or deliberate revenge for the burning of the Acropolis of Athens during the Second Persian War.
Do you have any questions?
MY QUESTION: How did Alexander take Persepolis?

QUES: Surely, you have noticed the tall poles along the roadside. Do you know what is on top of those poles? Thats right, wires that carry electric current. These wires carry electric current to your home. But what is electric current? Electric current is actually the flow of electrons. You may recall, an electron is the outer-most particle in an atom. They have a negative charge. Electricity is the continuous flow of these particles. Electrons are able to move through wires. Their speed can even be measured. The SI unit for electric current (or speed) is the ampere (A). Ampere is often shortened to amp. Electric current may flow in just one direction, or it may keep reversing direction. Direct current (DC) flows in only one direction. Direct current is what is used in devices like flashlights. Alternating current (AC) flows in two directions. This is the type of current that flows into your home through wires.
Do you have any questions?
MY QUESTION:
Do electrons have a positive or negative charge?