Work, Energy and Simple Machines

This man is straining to lift the weights on the exercise equipment. The weights aren't moving. So to a scientist, this man has done no work. Work is only accomplished when an object is moved a distance. A force is needed, and to provide the necessary force, energy is required. Energy is the ability to do work. In our machine oriented world, we have many tools and devices that help to get work done easier or faster. But as complicated as so many of these machines seem, they are all based on just 6 simple machines that were developed a very long time ago. The 6 simple machines are the liver, wheel and axle, pulley, inclined plane, wedge, and the screw. Today, we'll take a close look at three of these simple machines. A lever, wheel and axle and the pulley. The lever was one of the first simple machines. It is made up of two main parts. A bar that rotates or turns around a support point called a fulcrum. However, is used to move a resistance or load. The force necessary to move a load doesn't have to equal the weight of that load. The idea is to try and have the resistance close to the fulcrum, and the effort as far from the fulcrum as possible. The longer the effort arm, the greater the leverage, which means a small effort is required to produce a great force. Notice that the adult is easily lifted with one hand. The effort moves through a great distance. While the resistance only moves a short distance. The advantage is that the effort needed to lift the load is much reduced. There are actually three kinds or classes of levers. This board is being used as a first class lever. The fulcrum is located somewhere between the resistance and the effort. A nutcracker is an example of a second class lever. This time, the resistance is between the fulcrum and the effort. A third class lever is set up with the effort between the resistance and fulcrum. This rake is an example of a third class lever. If a hammer is being used to drive a nail, what kind of lever do you think it represents? The effort is the person's hand. The resistance is the hammerhead. The fulcrum is below the hand. So, the effort is between the resistance and the fulcrum. It is a third class lever. What kind of lever is a hammer, it is being used to pull a nail. It's a first class lever. The person's hand is providing the effort, the nail is the resistance, and the fulcrum, is located somewhere between the effort and resistance. A crowbar is used to pry two boards apart. The crowbar is being used as a lever. Think of where the resistance is. The effort and the fulcrum. It's a first class lever. The fulcrum is between the effort and resistance. The wheel was one of the most important inventions of all time. No one knows where the wheel was invented, but there is evidence that people living 6000 years ago used wheels. The wheel and axle is related to the lever. It is like a lever that has been wound up. The larger wheel represents the effort arm. And the axle represents the resistance arm. The bigger the wheel compared to the axle, the easier it is to use the wheel and axle. A steering wheel makes it easy to steer a car. A truck or a bus has a bigger wheel to help steer the larger vehicle. Skateboards, inline skates, and bicycles all use wheels and axles. A doorknob is another common example of a wheel and axle. It is easy to open a door because the door knob is like a wheel. If we remove the doorknob, we can see the axle that operates the door clasp. A bicycle uses the wheel and axle idea to make pedaling easier. The petals turn in a wide circle. The chain connects the pedal with the rear sprocket, which is smaller, and therefore turns many times each time the pedal goes around once. Another simple machine that is related to the wheel and axle is the pulley. The pulley has a wheel and axle built into it. There are two kinds of pulleys. One is called a fixed pulley, which means the pulley is attached to something. The object being lifted is attached to one end of a rope, the other end of the rope is fed through the pulley, and then a force is used to pull on the rope. The fixed pulley doesn't make lifting easier. It changes the direction of effort. The other kind of fully is the movable pulley. In this case the pulley moves with the object being lifted. Because of the way the rope is used, it takes only half the effort to lift the load. For example, this block of wood weighs 240 grams. But when lifted by a movable pulley, the effort needed is half as much. A combination of pulleys used together is called a block and tackle. A block and tackle can be used to lift heavy objects. When a machine makes work easier because it multiplies the effort being applied, we say the machine is providing a mechanical advantage. To find the mechanical advantage of a lever, you need to measure the length of the effort arm and the length of the resistance arm. Then divide the effort arm length by the resistance arm length. Remember lifting the adult with the first class lever. Let's measure the effort and resistance arms. The adult, who is the load in this case, is one meter from the fulcrum. The effort arm is four meters long. If we divide the effort arm by the resistance arm, we find the mechanical advantage is four. Another way of thinking of the mechanical advantage of four is to take the adults weight, which is 180 pounds, and divide it by four. The answer is 45 pounds of effort to lift the 180 pound adult. The mechanical advantage for a wheel and axle is determined by dividing the diameter of the wheel by the diameter of the axle. Let's calculate the mechanical advantage of this doorknob. The diameter of the wheel part is 5 centimeters. The diameter of the axle is two centimeters. Therefore, the mechanical advantage is 2.5. It's very easy to determine the mechanical advantage of a pulley setup. The mechanical advantage is equal to the number of supporting strands, so a movable pulley has a mechanical advantage of two. While a fixed pulley has a mechanical advantage of one. When more pulleys are added, the mechanical advantage increases dramatically. What this means is that if a block and tackle setup has four supporting strands, its mechanical advantages for. The amount of effort needed to lift an object is one fourth of the object's weight. If the object weighs 40 grams, it will take only ten grams of effort to lift it. The 6 simple machines have been important contributors to our advancement through the ages. However, not every application is succeeded. Take, for instance, this invention. You probably recognize the bike, what you probably didn't notice was the rocket extract to it. This inventor felt a locket recalled bicycle would revolutionize our means of travel. I guess there you got it right. Now, it's time for a video quiz. There will be ten questions. The first 5 will be multiple choice, and the last 5 are fill in the blank, or short answer. Question number one the turning point of a lever is called the blank. A resistance, B, effort, C fulcrum, D arm. Question number two the load or object being moved on a lever is called the blank. A resistance, B, effort, C, fulcrum, D, R. Question number three. The mechanical advantage of a wheel and axle is determined by a dividing the diameter of the wheel by the diameter of the axle. B, dividing the axle radius by the wheel radius. C measuring the length of the effort arm. D dividing the resistance arm by the effort arm. Question number four how do we calculate the mechanical advantage of a movable pulley? A, divide the length of the effort arm by the length of the resistance arm. V divide the wheel radius by the axle radius. C measure the length of the effort arm. D count the number of supporting strands of rope. Question number 5 how do we calculate the mechanical advantage of a lever? A divide the length of the effort arm by the length of the resistance arm. B divide the wheel radius by the axle radius. C divide the length of the resistance arm by the length of the effort arm. D divide the weight of the load by the effort arm. Question number 6 what is energy? Question number 7. How is a fixed bully different from a movable pulley? Question number 8. What is a block and tackle? Question number 9. Name the 6 simple machines. Question number ten. There are three kinds of levers. What makes them different from each other?