Simple Machines: The Inclined Plane Family (1959)

[Music] Many centuries ago, men were able to construct great buildings using only the simplest of tools. The engineers of the past were able to erect impressive temples and public buildings because they had learned to make use of many simple machines. One of these machines was the inclined plane. [Music] The ancient Egyptians built their colossal pyramids with the help of the inclined plane. They lifted the huge stones into place by dragging them up sloping piles of sand. For the Egyptians had discovered that it was a lot easier to push or drag an object up a slope than it was to lift it straight up. Let's find out just why it is easier. For our experiment, we'll need a half-finished pyramid and someone to take the place of the Egyptians. We'll use Mark, for he wants to know more about inclined planes, too. First of all, he's going to build up the pyramid by himself. He soon discovers that lifting a heavy concrete block is hard work. He'd find it a lot easier if he had a machine to help him. So, let's give him a plank. Yes, an ordinary plank can be a machine if it makes a job easier. If he puts the plank at a slant, Mark will have made an inclined plane. For an inclined plane can be any flat surface that has one end higher than the other. Mark will find the work a lot easier now that he can push the heavy block up a slope. It's easier because it takes less force. We'll prove that it takes less force in our next experiment. We'll need a board for our inclined plane and a brick to take the place of the concrete block. a spring balance to measure force. And of course, Mark, the brick weighs 6 lb. So, if Mark lifts the brick straight up, he has to use a force of 6 lb. Now, we'll see what force it takes to pull the brick up the slope with the brick being supported by the board. We only need to use four lb of force. 2 lb less than when the brick was lifted straight up. But how far do we have to move the brick each time? If we lift it straight up, we move the brick about 14 in, which is the height of the books. Using the inclined plane, however, we have to move the brick well over a yard. In each instance, the brick is raised 14 in above the table. And although we needed less force when we use the board, we had to move the brick a greater distance. What happens if we use a shorter board? This time the slope is naturally much steeper. Now the force needed to move the brick has increased to 5 lb. However, this time the brick has been moved a much shorter distance in order to raise it to the top of the books. Now watch what happens when Mark tilts the board even more. As the board goes up, it supports less and less of the weight of the brick until finally when it's straight up and down, the board doesn't take any weight at all. And the force needed to lift the brick is the full 6 lb. In our simple experiments, we've talked about force and distance. Multiplied together, they make up work. It took six lbs of force to raise our brick straight up to the top of the pile. If we use a plank to make our work easier, we only have to use a force of say 5 lb. But we have to move that force through a longer distance. If we increase the length of the plank, we need even less force, but we have to move the force a still greater distance. As you have seen, we always have to do the same amount of work. For as the force that we use gets smaller, the distance that we have to move it gets bigger. However, although the amount of work is the same, it's still a lot easier for us to do this work if we use an inclined plane. These movers are using an incline plane to move a heavy load. They found from experience that it's easier if they take it up a ramp. A wedge is another type of inclined plane. The thin end will go into the wood quite easily. And as the wedge is driven deeper, the sloping sides gradually force the log apart. Like the wedge, an axe is merely two inclined planes joined together. The point of a needle and the blade of a knife are also wedges that are made up of inclined planes. A common example in nature is a hill. Obviously, the shortest way to the top is straight up. But when the hill is too steep for us to climb, we build a road that goes up more gradually. Of course, you have to travel a longer distance to reach the top, but it takes a lot less force. This wood drill is very like our winding road. Here's the gradual slope of the incline plane winding its way to the top. Our hands aren't strong enough to press the drill through a 1-in piece of wood. But if instead of trying to push it down an inch, we turn the drill round and round many times, then we will have the force that we need to cut through the wood. Like the winding road, we've had to pay for the force that we needed by moving that force through a long distance. All types of screws are inclined planes. Let's do a little experiment that will show this quite clearly. The pencil has a piece of paper wrapped around it just like the spirals of a screw. If we unwind it, we get a perfect example of an inclined plane. With a simple screw, we can hold two pieces of wood together very tightly. With a screw jack like this one, one man without much effort can lift up the end of a heavy truck. The inclined plane, the simplest of all machines, has been in use for centuries and has helped to make our work easier in countless different ways. As a ramp, it helped Mark build his pyramid. And it helped the movers load their truck. It can take the form of a wedge or it can be one of many different types of screws. There's hardly a moment of the day that we're not putting it to use. Even if it's just for fun, Heat. Heat. [Music]