Topic
can the length of the handle on a hammer affect how well it can drive a nail into a piece of wood?
Introduction
Archaeologists tell us that about 35,000 years ago, people discovered that hafting a stone axe head by putting a handle on it gave them a distinctive advantage over simply holding the stone tool in their hands. Today, we take this simple innovation for granted. Without handles, tools such as hammers, hatchets, and cleavers would be much harder to use. A handle acts like a lever. All levers have a point on which they pivot: the fulcrum. in the case of a hammer handle, the fulcrum is the wrist of the person holding the hammer. if the person changes the position of the handle, he or she changes the location of the fulcrum. This affects how easily the tool will work. in this activity, you will test to see why a handle is an important addition to tools that you strike with and how changing its length affects how easily you get work done.
Time Required
30 minutes
Materials
● hammer
● 3 large nails (10d or larger) that are all the same size
● 3 pieces of 2-in. x 4-in. (5-cm x 10-cm) wood, each about 6 in. (15 cm) long
● ruler
● 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.
Procedure
1. Put on the work gloves and goggles. Using the ruler, measure the three nails to make sure they are the same length.
2. Pick up the hammer and hold it so that you are grasping the head directly. The handle should be pointed away from you (see Figure 1). Use your other hand to hold one of the nails steady in the center of one of the wooden blocks. Give the nail fi ve blows with the hammer. Be careful not to hit your fingers. After you have struck the nail fi ve times, use the ruler to measure how much of the nail is sticking out of the wood.
3. Take a second nail and block of wood. This time, hold the hammer by the handle, grasping the handle at the mid point. Give the nail fi ve blows with the hammer. After you have struck the nail fi ve times, use the ruler to measure how much of the nail is sticking out of the wood.
4. Take the last nail and block of wood. hold the hammer by the handle again, but now grasp the handle near its end. Give the nail fi ve blows with the hammer. After you have struck the nail fi ve times, use the ruler to measure how much of the nail is sticking out of the wood.
Analysis
1. Based on your data, how did changing the length of the hammer handle change the effi ciency of the hammer?
2. in which trial did the hammer feel most comfortable in your hand? Why?
3. in which trial did the hammer get the most work done? how do you know?
4. if you were going to chop down a tree, which type of axe handle would you want to use, a long one or a short one? Why?
What’s Going On?
When you use a hammer, the handle acts as a lever. A lever has two arms. The effort arm is the end to which you apply the force.
The resistance arm is the end at which the force is directed. in the case of the hammer handle, your wrist is the fulcrum, and your own arm is the effort arm. The hammer handle acts as an extension of your own arm. The longer the handle, the greater the force directed to the head of the hammer. Yet, the lever is not providing “free energy.” When you swing a hammer with a longer handle, you have to move it a greater distance. That extra distance translates into extra force.
in addition to getting more power out of the hammer, holding a handle toward the end also gives you more control over the tool. This cuts down on wasted motion.
Our Findings
1. In general, a longer handle on a device (such as a hammer) allows the user to gain more power with each stroke. Longer handles make devices more efficient.
2. The comfort when using a tool depends on the user. In general, a tool is most comfortable in a user’s hand when it is balanced. So the hammer might feel most comfortable when you are holding it near the mid point of the handle.
3. The most work should have been accomplished in the third trial, when the length of the handle was the longest. The trial data should have shown that the nail was driven into the wood deeper on this trial, compared with the first two trials.
4. An axe with a long handle has a greater mechanical advantage over an axe with a short handle.
Classes of Levers
Not all levers are created equally. Scientists have separated levers into three classes, based on where the fulcrum is and how the forces are applied. In a first-class lever, the fulcrum is between the load and the effort. In this type of lever, the effort force and the resistance force go in the same direction. Pliers and a balance scale are examples of first-class levers.
In a second-class lever, the fulcrum is at one end and the load is between the fulcrum and the point at which the effort is applied. The resistance force and the effort force go in opposite directions. A wheelbarrow is an example of a second-class lever; the wheel is the fulcrum.
In a third-class lever, the effort is applied between the fulcrum and the resistance. Like a second-class lever, the resistance force and the effort force work in opposite directions but the point at which the effort is applied is located between the fulcrum and the resistance. The user has to apply an effort force that is greater than the resistance force. The hammer that you used in Experiment 5: Testing Hammer Handle Length is an example of a third-class lever. The advantage of this type of lever is in the extra control that you gain. One of the most important examples of a third-class lever is the handle that flushes most toilets.
Topic
can the position of the fulcrum affect the mechanical advantage of a lever?
Introduction
levers are one type of simple machine. A simple machine is a device that gives the user a mechanical advantage. in science, work is accomplished when an object is moved from one place to another. every object, from the lightest feather to the heaviest rock, requires a force to make it move. This is called the resistance force. The effort force, as the name suggests, is the amount of force (or effort) used to get the work done. if the effort force is greater than an object’s resistance force, then the object will move, and work will be accomplished.
All simple machines reduce the amount of effort force needed to get a job done. They do this by increasing the distance over which the force is applied. The degree that a machine reduces the amount of effort needed is called the mechanical advantage. Simple machines create a mechanical advantage by moving the object a greater distance but with less effort. in the end, the amount of work that is accomplished is the same whether you use a machine or not.
A lever has two parts: a bar and a fulcrum. The bar moves, or pivots, on the fulcrum. The fulcrum divides the bar into two parts called arms (see Figure 1). The arm that holds the object being moved (called the load) is the resistance arm. The arm to which you apply the force is called the effort arm. in this activity, you will discover that moving the position of the fulcrum can give you a large mechanical advantage.
Time Required
30 minutes
Materials
● 12-in. (30 cm) ruler
● pencil
● 4 quarters
Safety Note Please review and follow the safety guidelines.
Procedure
1. create a lever by placing a pencil under the 6 in. (15 cm) mark of the ruler. The two ends of the ruler should balance on the pencil. in this setup, the pencil acts as a fulcrum. Place two quarters on the 12-in. (30-cm) end of the ruler and one quarter on the “0” end. The lever should now tip to one side. Record your observations and explain why this happens.
2. Without moving the quarters, change the position of the fulcrum so that the two sides of the lever balance again. Record the number of inches (cm) on the ruler at the point where you get the lever to balance again.
3. Keep the pencil in the new position and predict what will happen if you place a third quarter on top of the two that are already on the 12-in. (30- cm) end of the ruler. Add the third quarter and record your observations.
4. if you wanted to get the two ends of the lever to balance again, predict what you would have to do to the fulcrum. Try to balance the lever again and record your observations.
Analysis
1. Based on your observations, which end of the ruler was the force arm and which was the resistance arm? Why?
2. in which direction did you have to move the fulcrum in order to get the heavier weight to balance with the lighter weight?
3. in order to balance the three quarters, which end of the lever was longer: the resistance arm or the effort arm?
4. Based on your observations, how does moving a fulcrum affect the mechanical advantage of a lever?
What’s Going On?
With a lever, the amount of mechanical advantage is controlled by the position of the fulcrum. When the fulcrum is in the center of the bar, the force arm and resistance arm are equal lengths and the mechanical advantage is one. This means that the amount of force required to lift the load is equal to the resisting force of the load. one way to increase the mechanical advantage of a lever is to move the fulcrum closer to the load. This makes the effort arm longer, compared with the resistance arm. When you lifted two quarters with one quarter, you doubled the mechanical advantage of the lever. You did not gain free work, though. You had to move the lever a greater distance. in this case, the effort arm was twice as long as the resistance arm was. When you lifted three quarters with one quarter, you tripled the mechanical advantage, and the length of the resistance arm was tripled.
Our Findings
1. The arm with the multiple quarters is the resistance arm, because it has the load. The arm with the single quarter is the effort arm.
2. in order to lift a heavy weight with a lighter weight, the fulcrum must be moved closer to the load. This increases the length of the effort arm.
3. When lifting three quarters with one quarter, the effort arm was much longer than the resistance arm.
4. With a lever, moving the fulcrum closer to a load increases the length of the effort arm and increases the mechanical advantage.
Spear Throwers and Siege Engines
Spears were much better for hunting than simple hand axes. But spears still had a fairly limited range. Also, even the best spears had a hard time penetrating some animal hides. By about 15,000 b.c., hunters had discovered that they could use additional leverage to improve on a simple spear by launching it with a spear thrower. Called an atlatl by the ancient Aztec people, a spear thrower was usually made out of wood, antler, or bone. It looked like a long stick with a curved notch at one end.
A spear thrower extends the length of a hunter’s arm, giving him a greater mechanical advantage. The end of the spear is placed in the notch, and the hunter holds the other end of the spear thrower. When the hunter winds up to throw the spear, the longer effort arm (the hunter’s arm, plus the length of the spear thrower) means that the spear is released with a greater amount of force. This gives it more power to penetrate tough animal hides. This same type of device is still used by some Inuit today to throw harpoons, and it was the primary hunting tool of many people until being replaced by the bow and arrow.
During the Middle Ages, levers had a major impact on warfare. Before the cannon was invented, the only way that an army could bring down a stone fortress or castle was to bombard it with large stones from a siege engine. One of the most important of these siege engines was the trebuchet. Thought to originate in China in about a.d. 100, the trebuchet is designed to throw large rocks or other projectiles using a giant lever. A large lever is mounted unevenly on a fulcrum. The short end is the effort arm; it has a large weight (usually a box of rocks) hanging from it. The long end of the lever is the resistance arm. It is attached to a large sling that holds a rock or some other type of projectile. Unlike a catapult that gets its power from some type of spring, a trebuchet uses the movement of the weight to fire the projectile.
An aboriginal tribe member in Kimberley, Australia, uses an atlatl. By placing a spear in an atlatl, or spear thrower, a person’s arm length increases and this action provides more force in a throw.
A trebuchet uses the movement of weight to fire heavy objects long distances: The weight on the short end of the beam is released, pulling that side down and sending force to the other end of the beam, thereby firing the object.
Before the trebuchet could be fired, a team of men would pull down on the resistance arm, lifting the effort arm and its weight high above the ground. The weight was then locked into place. When the signal to fire was given, the weight was released. As gravity pulled it toward the ground, the force was translated through the fulcrum to the other end of the beam firing the rock. During the fourteenth century, some trebuchets were so large that they could fire a 220-pound (100-kg) rock a distance of 492 feet (150 m). That’s nearly the length of two football fields.
Levers in the Modern World
Everywhere you turn, you can see tools that are levers in action. Just about any tool with a handle uses a lever to give mechanical advantage. Picks, shovels, rakes, and brooms are examples of devices that gain added leverage by having handles. In Experiment 5: Testing Hammer Handle Length, you can discover how important a handle is for the function of a modern-day tool.
Topic
do the size and shape of a saw’s teeth affect how well it can cut a piece of wood?
Introduction
Based on the archaeological record, the fi rst true saws were used about 4,000 years ago. This is a time when people fi rst began fashioning tools from copper. drawings from ancient egypt dating back to about 1,500 B.C. show workers using a small saw to cut wood. The curved metal blade had a serrated edge and was attached to a wooden handle. These early saws were about the size of a large butcher knife, and they cut by ripping across the surface of the wood. in this activity, you will test to see why a saw blade can effectively cut through a piece of wood and see how the size of the teeth controls the way the blade cuts.
Time Required
45 minutes
Materials
● crosscut hand saw for wood with large teeth
● hack saw or coping saw with small teeth
● metric ruler
● 12 in. (30 cm) piece of 2-in. x 4-in. (5-cm x 10-cm) wood or similar sized wooden board
● 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.
Procedure
1. Put on the work gloves and goggles. Pick up the saw with the small teeth (hack saw) and examine the edge of the blade closely. Use the ruler to measure the length of the teeth. observe the shape of the teeth and record your description.
2. Take one piece of wood and lay it fl at on a sturdy surface (table or workbench). if possible, ask another person to assist you by holding the block of wood. Make sure that they put on work gloves and goggles, too. hold the saw by the handle and begin cutting across the top of the wood. observe in which direction the saw cuts and what happens to the sawdust as you cut. After making fi ve passes with the saw, remove it from the wood and examine the groove cut into the wood. compare the width of the groove with the width of the saw blade. Record your observations.
3. Pick up the saw with the large teeth (crosscut saw) and examine the edge of the blade closely. Use the ruler to measure the length of the teeth. observe the shape of the teeth and record your description.
4. hold the crosscut saw by the handle and place it on the wooden board so that it is about 3 in. (7.5 cm) away from the cut you made with the hacksaw. Begin cutting across the top of the wood with the crosscut saw.observe in which direction the saw cuts and what happens to the sawdust as you cut. After making fi ve passes with the saw, remove it from the wood and examine the groove cut into the wood. compare the width of the groove with the width of the saw blade. Then compare the width of the first groove you cut with the second groove. Record your observations.
Analysis
1. Based on your observations, in which direction did the hack saw cut, when you pushed it or when you pulled it? in which direction did the crosscut saw cut?
2. how did the width of each groove compare with the width of the saw blade that cut it? Why do you think this was so?
3. how did the width of the two grooves compare with each other? Why do you think this is so?
4. how did the depth of the two grooves compare with each other? Why do you think this is so?
5. Which saw required less force to cut width? Why?
What’s Going On?
When a saw cuts into a piece of wood, it makes a groove called a kerf. in order to keep the saw blade from “binding,” or getting stuck in the groove as it cuts, the kerf has to be wider then the blade itself. To do this, the teeth of the blade have to be “set” in opposite directions along the length of the blade. if you examine the two blades, you will see that half the teeth are bent to the left, and the other half are bent to the right. As the saw cuts into the wood, it also has to remove the sawdust from the kerf. otherwise the wood fi bers will fi ll up the groove and make the blade stick. To do this, the teeth on most saw blades are curved slightly so that they rake the sawdust out of the groove as they cut.
Most saw blades cut in only one direction. in general, saw blades that are small and thin like hack saws and copping saws cut the wood on the pull stroke. Saws with large thick blades usually cut on the push stroke. This is because a thin blade will bend more than a thick blade. By cutting on a pull stroke, the thin blade will stay straight as it cuts. if a thin blade cut on the push stroke, it would bend, causing the cut to curve. in addition, because more force is used on the cut stroke, pushing on a thin blade could make it snap.
Generally speaking, the larger the teeth on a saw blade, the more force is required to cut with it. Larger teeth also will result in a wider kerf with a more jagged edge. Blades with small teeth are used for fine detailed cutting, while blades with large teeth are used for coarse cutting.
Our Findings
1. Most hacksaws cut on the pull stroke, while most large cross cut saws cut on the push stroke.
2. I n both cases, the width of the groove cut by the saw blade was wider than the blade itself. This is because the teeth of the saw are bent slightly to the right and left along the edge of the blade. This keeps the blade from getting stuck in the groove as the blade cuts down.
3. The groove cut by the saw with the larger teeth was wider because the teeth were longer and more bent.
4. The groove cut by the saw with the larger teeth was deeper because the teeth were longer and removed more fibers as they moved cross the block of wood.
5. The saw with the smaller teeth requires less force to use because the small teeth did not make as large a bite in the wood.
Rock Saws and Cutt ing Concrete
As it turns out, not all saws have wedge-shaped teeth. Saws used to cut rocks (lapidary saws) and concrete use a different approach. Instead of having little wedges cut and chop at the surface, these blades use an abrasive material to grind their way through the rock. To do this, the abrasive on the blade has to be harder than the rock itself. Two of the more common abrasive materials used today are carbide steel and industrial diamonds. Yet, the rock saw is not a modern invention. In ancient Egypt, people were using a type of abrasive saw to cut through stone, too. Archaeologists believe that the rock saws they used had no teeth. Instead, these devices simply slid back and forth over the surface of the rock. The secret to their cutting power was a layer of wet quartz sand that was placed under the saw blade. Quartz is harder than many of the other minerals that the Egyptians were cutting. Examples of these primitive rock saws have yet to be found, but scientists do have several lines of evidence to show that they were used. Ancient drawings show workers cutting stone with sawlike instruments, and many of the stone coffins found in burial sites have saw marks on their lids.
Machines Made Simple
People usually don’t think of something simple, such as a hand axe or a saw, as a machine. In our modern world, the word “machine” is usually reserved for complex mechanical devices driven by engines or motors. It the strictest sense, though, all simple tools are machines: They all help to convert mechanical energy into useful work. To a scientist, the word work means moving an object over a distance. Over the years, scientists have come to recognize six basic machine types, all of which are classified as simple machines. We’ve already discussed one of them: the wedge. The other five are the screw, the inclined plane, the lever, the wheel and axle, and the pulley. As the term simple machine suggests, these devices are basic. They have few or no moving parts. They are important because they are used in many ways and are often components in much larger, compound machines. Simple machines work by trading force for distance. If you recall from Experiment 3: How a Saw’s Teeth Impact Cutting, a saw with small teeth requires less force to push, but you have to move it many more times, compared with a saw with large teeth. In the next two sections we’ll take a look at how all of the simple machines work. First, we’ll examine a second type of device put to work by humans. It’s the simple machine called the lever.
Looking at Levers
Like the wedge, a lever is a device that is used in many places. Levers are at work on a teeter-totter (or seesaw) on a playground, and on the handle that flushes a toilet. Early on, humans discovered that a lever could help them accomplish tasks that could not be done with a wedge alone. Take hunting, for instance. Although a simple hand axe was great for cutting and skinning an animal after it had been killed, it wasn’t useful for actually hunting game. That’s because in order to use a hand axe, you had to be very close to the animal. This didn’t work well for fast animals, such as deer, which could simply run away. A hunter could throw a hand axe at a large animal, but even if his aim was accurate, the blade would just bounce off the animal’s hide.
The solution turned out to be a simple one. By attaching the blade to the end of a long stick, the spear was born! Scientists aren’t sure exactly how long humans have been making and using spears, but based on the evidence, it’s believed to be about 100,000 years. Before people started using spears for hunting, they were probably using pointed sticks for digging up roots. A spear is such an effective weapon because it gives a person a type of mechanical advantage called leverage. In Experiment 4: Lifting with Levers, we’ll dissect how a lever works, so you can see for yourself where leverage comes from.
Topic
can the shape of a wedge affect how well it can split a piece of wood?
Introduction
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.
Time Required
45 minutes
Materials
● hammer
● 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.
Procedure
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.
Analysis
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.
Our Findings
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.
Topic
can a simple stone chopper be an effective cutting tool?
Introduction
These days, humans have many tools for cutting. Knives, scissors, saws, and axes can all be used to cut, chop, and slice through fabric, rope, wood, and even steel. each of these tools is an example of a device called a wedge. Wedges are implements that are wide at one end and gradually taper to a thin edge on the opposite end.
Before people had tools made of metal, they made simple cutting tools from stone, wood, and bone. Archaeologists tell us that the fi rst tools were stone choppers, used for cutting everything from animal hides to vines. in this activity, you will test to see how effective a simple stone chopper is at cutting a piece of rope.
● round rock about the size of a fi st
● rock about the size of a fi st, with a broken sharp edge
● 12-in.-long (30-cm) piece of 2-in. x 4-in. (5-cm x 10-cm) wood or similar
wooden block
● 2 identical pieces of nylon or cotton rope, each about 24 in. (60 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.
Procedure
1. Put on the work gloves. Take one piece of rope and grasp it in two hands. Try to rip the rope apart. Record your results.
2. Place the wooden block on a sturdy surface (table or fl oor). drape the piece of rope across the middle of the block (see Figure 1). Grasp the round rock in one hand and carefully strike the rope where it crosses the middle of the block. do this 20 times. Make certain that when you hit the rope with the rock, you are hitting it in the same place each time. Be careful not to hit your fi ngers with the rock.
3. Pick up the piece of rope that you just hit with the rock and observe it carefully. What happened to the fi bers of the rope? Record your observations. Try to rip the rope apart again and record your results.
4. Take the second piece of rope and grasp it in two hands. Try to rip the rope apart and record your results. Place the second piece of rope on the wooden block like you did with the rope in Step 2. Pick up the rock with the sharp edge and strike the sharp edge against the rope 20 times, the same way that you did with the round rock in Step 2.
5. Pick up the piece of rope that you just hit with the sharp rock and observe it carefully. What happened to the fi bers of the rope? Record your observations and then try ripping the rope apart. Record your results.
Analysis
1. What was the effect of hitting the rope with the round rock? Why?
2. What was the effect of hitting the rope with the sharp rock? Why?
3. Based on the results of the experiment, how might you improve the cutting ability of the second rock?
What’s Going On?
in order for an object to be an effective cutting tool, at least one edge has to be wedge-shaped. The sharper the edge, the easier it will cut. Modern cutting tools have extremely sharp edges, which allow them to easily split and separate the fi bers of the material being cut. early humans discovered that rocks with natural wedge shapes were better than rounded rocks at cutting and splitting materials. Rounded rocks could break fi bers by smashing them. Wedge-shaped rocks would split the fi bers apart, making it easier to separate them.
Our Findings
1. hitting the rope with a round rock will cause some of the fi bers to break, but it will probably not break enough of them to allow you to tear the rope apart.
2. hitting the rope with the sharp edge will cause the fi bers to split and tear. This is because the wedge-shaped edge cuts through the fi bers of the rope.
3. if you wanted to improve on the cutting ability of the sharp stone, you could use another rock to chip away at the edge so that it is smoother and more tapered. The more gentle the taper, the sharper the cutting tool.
Working with Wedges
Although simple stone choppers helped early humans carry out many tasks, their cutting ability was still limited. Through trial and error, people eventually discovered that they could make a better tool by sharpening both sides of the cutting face. They did this by using another rock called a “hammer stone” to gradually chip away at the edge of the chopper. This led to the development of a more sophisticated tool known as a hand axe. Unlike a simple chopper, the hand axe had a much narrower blade that was better for cutting.
Both the chopper and hand axe are examples of wedges. Many common woodworking tools used today are simply variations on a basic wedge design. Depending on the shape of the wedge, tools can be used for cutting, splitting, or shaving wood. In Experiment 1: The Wedge Design of a Stone Chopper, we saw how a wedge could be used for cutting. In Experiment 2: How a Tool’s Wedge Shape Affects Wood Split, we’ll examine which type of wedge is best at splitting a piece of wood.
A hatchet, like an axe, is an example of a wedge, a tool that is wide at one end and narrows to a point or edge at the opposite end. It is used for things such as cutting, chopping, and slicing.
The ability to intentionally create a tool for a specific purpose seems to be one of those traits that set humans apart from the rest of the animal kingdom. One of the first human species that made tools is Homo habilis. H. habilis lived about 2 million years ago. In 1960, Mary and Louis Leakey discovered the first H. habilis fossils at Olduvai Gorge in Tanzania. The Leakeys had been working at Olduvai Gorge for several years. They had found many simple tools that had been chipped out of stone. When they finally found fossil bones to go with the tools, Louis was convinced that he had found the remains of one of the earliest toolmaking humans. At the suggestion of another scientist named Raymond Dart, he gave the species the name Homo habilis, which in Latin means “handy man.” Many scientists question whether Homo habilis was truly the first toolmaker or even a direct ancestor of modern humans. In any case, there is evidence that humans have been making tools for a very long time.
Homo habilis was one of the earliest toolmakers. This species made simple tools out of stone. In fact, H. habilis’s remains in Tanzania and Kenya are often found buried near primitive stone tools these primates crafted.
Based on the archaeological record, it appears that the first manufactured tools were simple choppers created from rounded, fist-sized stones. Making a chopper is a fairly easy process. Hitting one edge of a stone with another stone of equal or greater hardness creates a jagged edge that could be used for cutting animal hides, sinews, small tree branches, and vines. Experiment 1: The Wedge Design of a Stone Chopper shows how effective a stone chopper is at cutting natural materials.
Humans are truly amazing creatures. Compared with many other animals on the planet, it might seem as if we are at a serious disadvantage. Ostriches can outrun us, elephants can out-pull us, and lions can rip us to pieces. Bats have better hearing, eagles have better eyesight, and even mosquitoes and wasps pack more of a sting. Despite all these limitations, we’ve done pretty well as a species. Th at’s because unlike most other animals, humans can make tools. Using tools, humans have molded and shaped the world. Tools also have allowed us to adapt to just about every environment on the planet. Th e truth of the matter is that without tools, humans probably would have become extinct a very long time ago.
When people hear the word tool, they usually think of objects such as hammers, screwdrivers, or even chain saws. Tools aren’t just for building, though. In fact, most of us can’t go more than a few minutes without using some type of tool. When you brush your teeth, you use a tool. When you eat your cereal or butter a bagel, you are using tools. Even pencils and pens are specialized tools. In the most general sense, a tool can be any device used to get a job done or make a task easier. Some tools, such as a sewing needle or a wrench, are simple. Th ey require only the force of a human hand to make them work. Other tools, such as a table saw or a drill press, are complex. Th ey have many moving parts, and motors or engines power them.
These days, people have an incredible variety of tools at their disposal to do all sorts of diff erent jobs. If you take a trip to a local hardware store or home improvement store, you can find hundreds of different devices for doing all sorts of tasks. Some tools, such as a pair of pliers, are versatile: They can be used for many different jobs. Others, such as a torque wrench, are designed for only one specific task. Regardless of a tool’s size, use, or complexity, our ability to make and use tools has been the driving force behind human evolution. Tools have taken us from being simple nomadic scavengers to space explorers and movers of mountains.
No one knows for certain how long humans have been making and using tools, but many scientists believe that we’ve been at it for at least 2.5 million years. We don’t have an exact date because we’re not sure what the first tools looked like. In addition, the historical record from this time is very spotty, so just finding true artifacts is very difficult.
Some of the earliest tools were made out of stone. They look similar to rocks that you might find lying around on the ground. In fact, unless you were trained in identifying tools, you would probably walk right over these rocks without even noticing them. Many scientists believe that before making tools, early humans began using stones for different tasks. Small rounded rocks were used to crack open nuts or break animal bones to get the marrow out. Rocks with sharp edges were used to cut through animal skins and tough plant material, such as vines.
Over time, humans discovered that they didn’t have to waste time looking for stones with the right shapes. Instead, they found that they could use one stone to chip away at another stone and shape it to fit the job. They learned that they could make tools to help them in their everyday lives.
