Imagine you are standing in a farm field in central Illinois. The land is so flat you can see for miles and miles. On a clear day, you might see a grain silo 20 miles away. You might think to yourself, it sure is flat around here. If you drive one hundred miles to the south, the landscape changes. In southern Illinois, there are rolling hills. Why do you think this is? What could have caused these features? There are no big rivers that may have eroded and deposited this material. The ground is capable of supporting grass and trees, so wind erosion would not explain it. To answer the question, you need to go back 12,000 years. Around 12,000 years ago, a giant ice sheet covered much of the Midwest United States. Springfield, Illinois, was covered by over a mile of ice. Its hard to imagine a mile thick sheet of ice. The massive ice sheet, called a glacier, caused the features on the land you see today. Where did glaciers go? Where can you see them today? Glaciers are masses of flowing ice.

Why does Springfield have its features?

Rolfe put down the little dog he had been holding, and went out into the hall. The dog accompanied him, frisking about him in friendly fashion. Rolfe first examined the bedroom that he had seen Inspector Chippenfield enter. It was a small room, containing a double bed. It was prettily furnished in white, with white curtains, and toilet-table articles in ivory to match. A glance round the room convinced Rolfe that it was impossible for a man to secrete himself in it. The door of the wardrobe had been flung open by the inspector, and the dresses and other articles of feminine apparel it contained flung out on the floor. There was no other hiding-place possible, except beneath the bed, and the ruthless hand of the inspector had torn off the white muslin bed hangings, revealing emptiness underneath. Rolfe went out into the hall again, and entered the room next the bedroom. This apartment was apparently used as a dining-room, for it contained a large table, a few chairs, a small sideboard, a spirit-stand, a case of books and ornaments, and two small oak presses. Plainly, there was no place in it where a man could hide himself. The next room was the bathroom, which was also empty. Opposite the bathroom was a small bedroom, very barely furnished, offering no possibility of concealment. Then the passage opened into a large roomy kitchen, the full width of the rooms on both sides of the hall, and the kitchen completed the flat.

In what room did Rolfe find a double bed?

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.
What are two types of electric current?