can the shape of a wedge affect how well it can split a piece of wood?
Many tools that we use today have a wedge-shaped design. A knife, the blade of a screwdriver, an ax head, and a chisel are all variations on a simple wedge. Some of these tools are made specifi cally for cutting. others are more effective at splitting. The shape of a wedge controls its ability to either cut or split. in this activity, you will test to see how the angle of a wedge controls how effective it is at splitting a piece of wood.
● flat-bladed screwdriver
● thick, steel chisel (the type used for splitting brick)
● 2 pieces of 2-in. x 4-in. (5-cm x 10-cm) wood, each about 6 in. (15 cm) long
● safety goggles
● work gloves
Safety Note This activity requires adult supervision. Make certain that you and anyone near you are wearing goggles and work gloves during this activity. Please review and follow the safety guidelines.
1. Put on the work gloves and goggles. Take the screwdriver and examine itclosely. describe its shape. Predict what will happen when you use the hammer to tap the screwdriver into the wood.
2. Take one piece of wood and lay it on end on a sturdy surface, such as a table or fl oor. if possible, ask another person to assist you by holding the block of wood steady. Make sure that they put on work gloves and goggles too. hold the screwdriver straight up and down so that the blade is in the middle of the wood block (see Figure 1).
3. Using the hammer, gently tap the handle of the screwdriver 10 times so that you drive the blade into the wood. Be careful not to hit anyone’s fi ngers with the hammer. observe what happens to the wood. Write your observations on the data table.
4. Pick up the chisel and examine it closely. compare the shape of the chisel to the shape of the screwdriver. Pay close attention to the angle that the wedge makes. Based on what happened with the screwdriver, predict what will happen if you use the hammer to drive the chisel into the wood.
5. Take the second piece of wood and place it on a sturdy surface, as you did with the fi rst block. Place the chisel on the second piece of wood in the same position as you did the screwdriver in Step 2. Tap the chisel with the hammer 10 times and drive it into the wood. observe what happens to the wood.
1. What happened to the wood when you tapped the screwdriver into it?
2. What happened to the wood when you tapped the chisel into it?
3. Which tool required more force to drive it into the wood? Why?
4. if you were splitting logs for a fi replace, what shaped wedge would be the best to use?
What’s Going On?
Many woodworking tools are wedge-shaped. The angle of the wedge on each of these tools has a different shape, depending on its purpose. Tools that have a thin blade with only a slight taper, such as a screwdriver, can be driven into a piece of wood without causing the wood to split too much. That’s because the angle of the wedge is small and only causes a few wood fi bers to break when it enters the block. Tools that have a thick blade, such as the chisel, have a wedge with a much wider angle. As it enters the wood, the wedge forces apart many more wood fi bers. This puts a great deal of stress on the block. if enough force is used, the piece of wood eventually will split. carpenters use a variety of wedge-shaped tools for working with wood. each tool has its own special shape. A plane has a thin blade that is sharpened on only one side. This makes it ideal for shaving off strips of wood. A maul has a thick blade specifi cally designed to split a piece of wood. in general, the smaller the angle on the wedge of the tool, the thinner the blade, and the less force needed to use it.
1. When the screwdriver was hit with the hammer, the blade should have gone easily into the wood and the wood should not have split too much.
2. When the chisel was hit with the hammer, there should have been much more resistance and the wood block should have shown signs of splitting, if it did not split completely.
3. Because the chisel has a much wider wedge with a larger angle on the blade, it requires much more force to drive it into the block of wood.
4. I f you want to split logs, you would use a very thick wedge with a large angle at the tip.
Wedges in the Modern World
Today, wedges are used for a variety of jobs. Many doorstops are wedges made of wood or rubber. The doorstop fits between the bottom of the door and the floor. The wedge-shaped design forces the door and floor apart, holding the door open. Wedges also are used for keeping doors closed. Take a close look at the edge of a door where the doorknob is. When you turn a doorknob, a wedge-shaped piece of metal moves in and out of the doorframe. This simple design allows the door to slide closed and lock in place. Wedges also are used in zippers. Most zippers have two rows of teeth that get locked together when the slider passes over them. If you examine the inside of the slider closely, you’ll see that there are two wedge-shaped guides. When the slider passes over the teeth, the two wedges line the teeth up and make them mesh together. When you unzip, the wedges pry the teeth apart again.
Wedges don’t have to be flat to be useful. A sewing needle, a pin, and an awl are wedges, each with a round shape. The point of a pencil and the tines of a fork also are wedges. When it comes to building things, one of the most important wedges is a simple nail. When you hammer a nail into a piece of wood, the point of the nail forces the wood fibers apart, creating pressure on the board. It is this pressure that keeps the nail stuck in the wood and helps to hold many buildings together.
Of course, before you can nail two pieces of wood together, you have to be able to cut the wood. Today, almost all of the lumber used for buildings and other construction projects is cut using saws. Compared with the hand axe, the saw is a fairly recent invention. The first true saws didn’t come about until people started making tools out of metal. Though many of the chipped stone tools used in earlier times had serrated blades, they were not saws. People would have had big problems using these tools to try to cut wood. Most stone tools, like the hand axe, had fairly thick blades with wide-angled wedges. This would have made it difficult for the blade to cut very deeply into the wood. If a person tried to use it to cut back and forth, the wide part of the blade would get stuck in the groove that was being cut. Also, as it cut, a stone blade would leave all the wood fibers in the groove. This would plug up the groove with sawdust, making it impossible to cut further.
For a saw to work properly, it needs a different design. Rather than simply chopping at the wood, the teeth of the saw have to cut and remove wood fibers as the saw slides back and forth. It is possible that the idea for saw teeth came from animal teeth. Some scientists believe that hunters had tried to use the jawbones of animals, such as deer, for cutting through small branches. By running the teeth over the wood, they could gradually break through the fibers, making a relatively straight cut. The first metal saw looked a lot like a large kitchen knife with a row of wedge-shaped teeth along the cutting edge. In Experiment 3: How a Saw’s Teeth Impact Cutting, you’ll discover for yourself the unique design that makes a saw so effective for cutting wood.