| How a Pendulum Works: A pendulum is made up of a string or solid rod with a weight attached to the end. Pendulums are designed in such a way that once they are moved, they will continue to swing for a long period of time. Gravity is the force that keeps the pendulum moving. Pendulums are often used in clocks because it takes the same amount of time for it to swing in one direction as it does for it to swing in the other direction. The amount of time it takes for a pendulum to swing from one side to the other and back again is called a “period.” A pendulum whose period is 4 seconds takes 2 seconds to swing to the left and 2 seconds to swing back to the right. |
| How a Mechanical Clock Works: Mechanical clocks tell time using gears. They have two important parts: a mainspring and a pendulum. Mechanical clocks are wound with a key, and this tightens the mainspring. As the mainspring unwinds, its energy turns gears which cause the hands to move. The pendulum keeps time and ensures that the gears move at the right pace: second by second. Instead of a mainspring, some mechanical clocks have weights that pull the gears at the right pace. Mechanical clocks do not need electricity to operate. They can run off of the energy generated by their springs and weights. |
| How an Incense Clock Works: The incense clock was invented in China between the years of 960-1279 and was very popular in Eastern cultures. All incense clocks used burning incense to measure time, but there were many types. For example, some used color. The smoke from the incense would be one color for a period of time, and then it would change, showing that a certain amount of time had passed. Some incense clocks used smell to show the passing of time. They would be divided sections of different smells, and when the observer noticed a different smell, they could determine what time it was. Some incense clocks would burn underneath of threads with weights attached. After a certain amount of time had passed, the fire from the incense would burn the thread, causing the weight to drop onto a gong below. This was an “alarm” for someone who wanted to know what time it was. |
| How a Candle Clock Works: Candle clocks used tall candles to show the passing of time. The candles had evenly spaced lines on them that were usually marked with numbers for each hour. When the candle burned down to one of the numbers, it showed what time it was. Sometimes the candle just had the lines and no numbers. In this case, the observer would have to know how long it took for the candle to burn from one line to the next. For example, if they knew it took exactly 15 minutes for the candle to burn from one line to the next line beneath it, then after 2 lines, they would know that 30 minutes had passed. |
| How a Water Clock Works: A water clock, also known as a clepsydra uses a flow of water to measure time. There are two types of water clocks: inflow and outflow. In an outflow water clock, a container is filled with water, and the water is drained slowly and evenly out of the container. This container has markings that are used to show the passage of time. As the water leaves the container, an observer can see where the water is level with the lines and tell how much time has passed. An inflow water clock works in basically the same way, except instead of flowing out of the container, the water is filling up the marked container. As the container fills, the observer can see where the water meets the lines and tell how much time has passed. |
| How an Atomic Clock Works: Atomic clocks operate by measuring energy particles. Although their name might sound dangerous, atomic clocks are not radioactive. Atoms, the smallest unit of matter, are always changing their energy state from positive to negative. An atomic clock measures the amount of time it takes for an atom to switch its energy state. It counts how many times the atom switches from positive to negative and vice versa and then uses that number to measure the passing of time. |
| How a Quartz Clock Works: Quartz clocks operate using the mineral quartz inside of a clock to keep time. Like mechanical clocks, quartz clocks still use gears to count time, but they are electrical. The mineral quartz is piezoelectric. This means that when a quartz crystal is squeezed, it generates a very small current of electricity. This also means that when electricity is passed through the quartz crystal, it vibrates. Quartz crystals all vibrate at the same frequency, meaning they shake the same number of times each second. Quartz crystals vibrate exactly 32,768 times each second! All quartz clocks contain a battery to vibrate the quartz crystal and a circuit to count how many times the crystal has shaken. The circuit then uses this information to create regular pulses of electricity. It generates one pulse every second. These pulses then make the gears of the clock move (if it is a mechanical clock) or power a digital display (if it is a digital clock). The quartz crystal in a quartz clock helps keep the clock accurate. |
