SLINGSHOTS, CATAPULTS, AND CANNONS:
What’s the fastest you can throw a baseball? How far can you kick a football? With years of practice and training, the best athletes in the world can kick, hurl, and toss objects incredible speeds and distances.
But even the fastest and the strongest athletes can’t throw a boulder the length of a soccer field or fire a pitch at 300 miles per hour. To hurl projectiles farther and faster, people need the help of machines.
ESSENTIAL QUESTION
Why do people keep inventing new and improved ways of sending projectiles through the air?
machine: a device that transmits a force or motion.
work: a force that moves an object a distance.
pulley: a simple machine consisting of a wheel with a grooved rim that a rope or chain is pulled through to help lift a load.
atlatl: a spear-thrower.
energy: the ability or power to do things, to work.
MACHINES
What do hammers, wheels, and bows have in common? All are examples of machines. Machines can be complicated, such as an airplane, or they can be simple, such as a hammer. Machines can come in different sizes and can have many uses.
A machine is anything that helps you do work. In this book, when we talk about work, we’re not talking about your homework or a person’s job. Work is done when a force moves an object. And machines can make this work easier. A system of pulleys does work by helping lift heavy things you could never lift on your own, while a bow can shoot an arrow farther and faster than even the best Olympic athlete could ever throw.
DID YOU KNOW?
Which sports make use of machines to get things moving farther and faster? What would baseball be like without a bat? What about ping-pong without a paddle? Lots of sports use machines to get things moving. Can you think of some others?
One of the earliest examples of a machine is the atlatl. This spear-thrower helps increase the distance and speed a person can throw a spear.
Atlatls help people throw spears farther and faster by acting as an extension of the thrower’s arm. The atlatl’s extra length and mass increase the amount of work a thrower can do by giving the spear more energy. To get bigger projectiles moving farther and faster, you’ll need all the energy you can find!
kinetic energy: energy associated with motion.
potential energy: energy that is stored.
gravitational potential energy: the energy an object possesses because of its position in a gravitational field.
mechanical energy: energy that uses physical parts you can see, such as the parts of a machine. It is related to motion and height.
ENERGY
You probably hear the word “energy” a lot. There’s solar energy from the sun, chemical energy in batteries, electrical energy, and nuclear energy, just to name a few.
Do you have a lot of energy? Sure! When you’re running a race or riding a bicycle, you have kinetic energy. Kinetic energy is the energy of motion. A basketball sailing toward the hoop and a car cruising down the road both have kinetic energy. When you apply a force to something and it moves, you’re increasing its kinetic energy. The amount of kinetic energy something has depends on its mass and velocity. A moving car has more kinetic energy than a bicycle going the same speed, and a hard-struck soccer ball has more kinetic energy than a soft pass.
But things don’t have to be moving to have energy. When you pick up a ball, you’re giving it kinetic energy. But if you stop lifting and just hold the ball, where did its energy go? The kinetic energy is changed into something called potential energy. You can think of potential energy as stored energy, kind of like a battery.
Runners at a starting line have potential energy. When they take off, their potential energy is changed into kinetic energy.
If you drop the ball, the force of gravity accelerates it, turning the potential energy back into kinetic energy. This potential energy is called gravitational potential energy.
Gravitational potential energy depends on an object’s mass and height. The higher something is, the more potential energy it has. A book on a bookshelf has more gravitational potential energy than a book on the floor. And a big dictionary has more potential energy than the small paperback on the shelf because the dictionary has more mass!
DID YOU KNOW?
Have you heard the phrase “the bigger they are, the harder they fall”? How does it relate to potential energy?
There are many kinds of potential energy. Batteries hold electric potential energy. Food has chemical potential energy, which our bodies change into kinetic energy to get us moving. Springs, rubber bands, and even twisted string have elastic potential energy, which becomes kinetic energy when these are released.
Conservation of Energy
Where does energy go? When a ball rolls to a stop, where did its energy go? Energy doesn’t disappear—it can only be turned into another kind of energy. Friction can transform the energy of motion into heat, while placing a book on a shelf transforms its kinetic energy into potential energy. This is called the conservation of energy. It means that energy can’t be created or destroyed—it can only be changed from one form to another. In fact, all the energy in the universe changes only from one kind of energy to another.
Together, kinetic and potential energy make mechanical energy. The ability to do work, or to get moving, is called mechanical energy. While you can’t see kinetic and potential energy, you can see the work that they do.
Imagine a marble balanced at the top of a ramp. What kind of energy does it have? If the marble starts to roll down the ramp, what kind of energy does it have now? Imagine there’s a cup at the bottom of the ramp. When the marble hits it, the cup goes flying! What is that energy called?
The kinetic and potential energy of an object can change from one form to the other, depending on how the object is moving and its position. When the marble is at the top of the ramp, it has only potential energy. But when the marble is rolling down the ramp, its potential energy is changed into kinetic energy. When the marble hits the cup, the mechanical energy of the marble does work on the cup—it moves the cup!
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When you increase the mass of the marble or increase its starting height, you increase the mechanical energy of the marble, and it moves the cup farther. But if you decrease the mass of the marble or lower its starting height, the marble has less mechanical energy, and moves the cup a shorter distance.
In ballistics, mechanical energy is very important. The more energy you have, the higher, farther, and faster you can you throw, toss, and fire your projectiles. And for centuries, people have been building machines to do just that. Whether it’s an atlatl, a bow, a catapult, or a gun, they all turn potential energy into kinetic energy to send projectiles on their ballistic trajectories.
A catapult at Castelnaud Castle in France. This site from the Middle Ages has many re-creations of weapons that were used in past centuries.
Have you ever stretched out a rubber band only to have it snap back on your hand? Ouch! The energy in the band to snap your fingers happens when the elastic potential energy of the stretched rubber band is turned into kinetic energy. Slingshots also use elastic potential energy to fire projectiles on ballistic trajectories.
Although they look like an old and simple tool, slingshots have been around only since the 1850s, when rubber was invented.
Simple slingshots can be made from a Y-shaped piece of wood or other sturdy material, with a strong but flexible elastic band stretched between the upper parts of the Y. When someone grips the bottom of the Y as a handle, the elastic band can be pulled back to increase its potential energy and then released to convert it to kinetic energy. Zing!
BOWS AND ARROWS
Slingshots are not the only things that use elastic energy to power projectiles. The bow and arrow, one of the most ancient tools of hunters and soldiers, is still popular today. From the tales of Robin Hood to The Hunger Games, archery has appeared in legends and stories old and new.
The tools of an archer can be different depending on their history and purpose, but the basic parts are the same. All bows consist of two main parts: the bow and the bow string. When the bow string is drawn back, the bow bends, increasing the elastic potential energy of the bow. When the bow string is released, it snaps back. As the potential energy from the bow is converted to kinetic energy, it moves the bow string and the arrow, quickly accelerating the arrow to its target.
The earliest evidence of archery comes from South Africa, where stone arrowheads dating back more than 64,000 years have been found in rock formations.
For ancient people, creating bows and arrows was a difficult process.
A strong but flexible wood was needed for the bow. A tough string, made of plant and animal fiber, needed to be strong enough to bend the bow without breaking. And carving straight arrows that flew well was a challenge of its own. As centuries passed, different cultures made their own sizes and shapes of bows and arrows, each designed to fit the needs of their unique cultures.
The Tale of Robin Hood
Have you heard of Friar Tuck or the Sheriff of Nottingham? The centuries-old stories of Robin Hood and his band of thieves are still told today. Supposedly, they stole from the rich to give to the poor. But was Robin Hood a real person?
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Bows can come in many shapes and sizes, but three types are the most common. The longbow is the simplest kind of bow, used by different cultures and peoples around the world. The longbow was used for hunting, sports, and in battle, especially during the Middle Ages.
DID YOU KNOW?
Smaller versions of the longbow are called short bows. They are mostly used today to teach archery to beginners.
The English were very successful using the longbow, and it’s featured in many English tales and legends, including Robin Hood.
Longbows were usually big, around 4 to 5 feet tall, and made of a strong but flexible yew wood. During battles in the Middle Ages, hundreds of archers would fire with longbows at once, raining deadly arrows down on their enemies from great distances.
Battle of Crécy between the English and French in the Hundred Years’ War Jean Froissart (1337–1410) This painting shows bowmen fighting a battle with longbows. What other devices can you spot that use projectiles?
recurve bow: a bow with limbs that curve away from the archer when unstrung.
compound bow: a bow that uses a levering system, often cables and pulleys, to bend the limbs.
mechanical advantage: the amount a machine multiplies a force to make a task easier.
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The recurve bow is smaller than the longbow, which makes it easier to carry and shoot. Recurve bows were first used in Mongolia, where riders on horseback found that its smaller size made it easier to shoot while on the move. You might think that a smaller bow would be less powerful, but its shape helps make up for its difference in size.
Gwen Sheppard uses a recurve bow during the archery competition of the 2012 Warrior Games. Sheppard is with the Air Force team.
credit: U.S. Air Force/Val Gempis
The word “recurve” comes from the extra curve of the bow, which bends back on itself. This extra curve stops the string earlier and quicker than the longbow, delivering more energy to the arrow. Today, recurve bows are used in many archery competitions, including the Olympic Games.
U.S. Invictus team archer Chasity Kuczer competes with a compound bow at the 2016 Invictus Games.
credit: DoD News photo by EJ Hersom (CC BY 2.0)
Recurve bows and longbows are excellent tools for launching arrows, but they both need a lot of strength and stamina to use—which can quickly tire out archers. The compound bow is designed to lessen the amount of strength an archer needs. Compound bows use pulleys to help increase the energy delivered to the arrow while requiring less strength to draw the string back.
Thanks to this mechanical advantage, compound bows can be smaller than both longbows and recurve bows, while still firing arrows with even greater force and accuracy.
Slingshots and bows are great for hitting targets with precision, but their projectiles are small. What if you want to send something bigger on a ballistic trajectory? What would happen if you tried to launch a bowling ball with a slingshot or put a basketball on the tip of an arrow? The laws of motion say that to accelerate a bigger mass, you need a greater force. So what kind of machine can throw heavy things great distances? Catapults!
engineer: a person who uses math, science, and creativity to solve problems or meet human needs.
fortification: a walled-in area to protect against an enemy.
mangonel: a military device for throwing stones and other projectiles.
biological warfare: the use of toxins or other biological matter as weapons.
payload: the object or load that is being delivered by the catapult.
torsion: a twisting force that turns or twirls a material.
tension: a pulling force that pulls or stretches an object.
SIEGE ENGINES: THE CATAPULTS
In the Middle Ages, stone walls were used to protect kingdoms and castles from invaders. Castles were built with especially thick stone walls and were sometimes surrounded by moats and other traps to keep armies from approaching. Archers often lined the tops of the walls, ready to rain down arrows on anyone who got too close. Attacking forces would lay siege to these well-defended places, often surrounding the towns and castles just outside their walls. But castles were often filled with food and supplies, and the people inside would try to wait out any attack if the walls held.
This gave engineers a difficult problem to solve. If archers and swordsmen couldn’t break through a wall, what could be done? The answer was to build siege engines. Siege engines are machines built to help forces break through walls—or go over them. One effective and deadly siege engine was the catapult.
Catapults are large machines that toss heavy objects such as boulders, spears, and even fireballs on ballistic trajectories at and over enemy fortifications. If an attacking army had catapults, it could possibly break through even the thickest walls. If that failed, it could use the catapults to send crushing stones and fire raining down on people inside the walls. One of the most common catapults is called a mangonel.
DID YOU KNOW?
The catapults you might have seen in pictures or movies were the kinds first used in the Middle Ages, but similar machines were used thousands of years ago by the Chinese, Greeks, Romans, and others. Like archery, catapults were used by many cultures around the world.
Catapults weren’t used only to heave heavy stones or fireballs. Sometimes, they were used to spread disease. In 1346, while laying siege to the city of Caffa, the Mongol army used catapults to hurl plague-infected corpses over the city walls. The bubonic plague, also called the Black Death, spread quickly and killed thousands who had no escape from the surrounding Mongol armies. The survivors fleeing the siege spread the plague into Europe. Catapult-spread plague is one of the earliest examples of biological warfare.
MANGONEL
The mangonel was first used by the Romans around 400 BCE. Mangonels have a long arm with a bowl-shaped platform on one end to hold the payload. The arm is attached to an axle, which is wound with many ropes. To prepare the mangonel to fire, the arm is slowly pulled back, twisting the ropes around the axle, creating torsion. This can produce a lot of potential energy.
When the arm is released, the tension in the ropes causes the arm to snap back with tremendous force until it is stopped by a crossbar, and the projectile is thrown toward the target.
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The launch angle can be changed by raising or lowering the crossbar. This allows the crew to change the ballistic path of the projectile.
missile: an object or weapon that is propelled toward a target.
counterweight: a weight that balances another weight.
fulcrum: the point on which a lever rests or is supported and on which it pivots.
ballista: a large crossbow for firing a spear. Plural is ballistae.
Mangonels have a few disadvantages. The stretching and twisting of their ropes can cause them to weaken and break over time, making them less accurate. A stronger and more accurate type of catapult is the trebuchet.
The earliest trebuchets are thought to have been made in China around 300 BCE. Like the mangonel, a trebuchet has a long arm used to throw projectiles with great force. But instead of using torsion to power their missiles, trebuchets use gravitational potential energy.
DID YOU KNOW?
Some of the things people used as projectiles with mangonels included burning sand, dead animals, feces, sharp wooden poles, and vats of burning tar.
These trebuchets were reconstructed at Castelnaud Castle.
A trebuchet has a long arm, or lever, attached to a heavy counterweight. The arm moves around a fulcrum, which is closer to one end than the other. The counterweight is attached to the shorter end of the lever, and the payload is held in a pouch and a sling attached to the longer side.
To fire the trebuchet, the long end of the arm is pulled down, lifting the counterweight into the air. This gives the trebuchet a lot of gravitational potential energy. While the arm is held in place, the projectile is loaded into a sling. When the arm is released, the counterweight drops, the arm whips through the air, and the payload is launched with great speed toward its target.
Punkin Chunkin
Catapults, like mangonels and trebuchets, have been around for centuries. But just because they’re old doesn’t mean they aren’t fun! There are competitions around the world to see who can fling objects the greatest distance using these ancient technologies. One of the most popular projectiles is a pumpkin!
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Because gravity pulls on the counterweight with the same amount of force every time, trebuchets are more accurate than the rope-twisting mangonel, and they don’t break as often!
The word trebuchet comes from the French word trebucher, meaning “over throw.”
Trebuchets are very good at lofting heavy stones and other deadly projectiles to great heights, making them especially useful for throwing things over towering defenses. But they weren’t very useful for nearby foes. Instead, many armies used the ballista when opposing forces came too close.
crossbow: a weapon used to shoot arrows.
bullet: the projectile used in guns.
barrel: a hollow tube that holds a projectile.
chemical potential energy: energy that results from a chemical reaction.
controversial: likely to cause the public to disagree and argue over something.
BALLISTAE
One of the deadliest types of catapult was the ballista. Ballistae are like crossbows, but much larger. These lethal weapons were fired almost straight ahead into the charging enemy.
Ballistae use torsion and tension to power projectiles. Two wooden arms are attached to ropes, which are twisted together and drawn back. Once the string is locked into place, large arrows or bolts are loaded into the center track and aimed at the target. With the release of the bow string, the ropes unwind, propelling the deadly projectile at the enemy.
Mangonels, trebuchets, and ballistae are just a few of the many different catapults that were used for centuries. They were often built on wheels so they could be moved into just the right position. They dominated battlefields until a more powerful weapon came along: firearms.
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Compared to modern guns, the first firearms were not very good. The earliest examples, called fire lances, were made in tenth-century China. Fire lances were long tubes made of bamboo filled with an early form of gunpowder. They were dangerous, but not very accurate. They were just as likely to explode as they were to hit their target.
DID YOU KNOW?
Although they might resemble a rifle, BB guns and air rifles aren’t really firearms. Instead of using a chemical reaction, they use compressed air to send a BB or pellet at a target.
Firearms all work in the same basic way. A projectile, called a bullet, sits inside a barrel. But instead of using elastic or gravitational potential energy, firearms use chemical potential energy. When gunpowder is ignited, gases expand very quickly inside the barrel, converting the potential energy into kinetic energy and pushing the projectile out of the barrel at an incredible speed.
As the technology of firearms spread around the world, weapons such as cannons and muskets replaced catapults and archers in battle. Stone walls were no match for the violence and destruction of a heavy cannonball fired at high speed.
Bullets are some of the fastest projectiles around. The quickest can achieve speeds of 1,700 miles per hour, more than twice the speed of sound. It’s this speed that gives dangerous weapons such as cannons, mortars, and guns their range and power. The ability of modern guns and rifles to cause harm and destruction makes them a very controversial topic around the world.
Now that you know how projectiles are launched in the air, we’ll look at some of the things these projectiles can do while they’re up there!
ESSENTIAL QUESTION
Why do people keep inventing new and improved ways of sending projectiles through the air?
ATLATL BATTLE
Different kinds of spear-throwing tools were used by ancient people around the world, but they all worked in the same basic way. It takes a lot of practice to use an atlatl, but you can make your own and try it out at home!
Warning: Never point or fire any weapon at a living creature and always wear eye protection. Ask an adult to help with the knife in this activity.
›Attach one binder clip to one end of the ruler. This is the “spur.” Fold the clip handles back.
›Using a small knife, CAREFULLY carve a notch into the eraser of each pencil. The notch should go about half way into the eraser and be wide enough to fit onto the binder clip handle. The pencils will be your darts.
›Place an eraser cap on the unsharpened end of the pencil. This will help your dart fly and be much safer!
›Place the binder handle into the notch in the eraser and lay the pencil onto the ruler lengthwise.
›Attach binder clips on either side of the pencil. These will help keep the dart from sliding off the sides of the ruler. DO NOT clip the pencil to the ruler. The pencil only needs to rest on the ruler.
›In a safe and open space, hold the ruler at the end opposite the spur. Don’t hold onto the pencil! It should only rest on the ruler.
›Keeping the ruler flat and level so the dart can’t slide out, reach back, and quickly bring the ruler forward like you’re throwing a paper airplane. Turn your wrist down at the end of the motion. Don’t let go of the ruler!
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›What happened? Was the motion what you expected? Using an atlatl takes a lot of patience and practice!
Questions to think about
How is the atlatl a machine?
What forces are acting on the dart as it’s thrown?
What forces are acting on it once it’s released?
What other motions are like the one you use to throw the dart?
Try This!
Try hitting a target! How accurate can you be? What might make your dart more accurate? How far can you throw? Try comparing the atlatl to simply throwing your dart. Which gives you greater range?
Does adding weight to the dart or the atlatl make a difference? Try making a larger atlatl to throw even larger darts. How far can you throw?
Modern slingshots use special elastic materials and different shapes to give shooters even more accuracy and power. But you can make your own!
Warning: Never point or fire a slingshot or any other weapon at a living creature. Always wear eye protection.
›Cut two rubber bands into single strips of the same length.
›Tie the first rubber band to one branch of the Y and the second rubber band to the other branch. Be sure to tie them tightly! If you need to, secure them to branches of the Y using tape.
›Out of leather or sturdy cloth, cut a rectangular pouch to hold your projectiles. Cut or punch two holes on either side of the pouch.
›Tie a rubber band to each hole in the pouch and reinforce them with tape.
›Find a large, open space outdoors to test your slingshot. Place your projectile in the pouch and launch it! Aim at an appropriate target, such as a piece of paper or a tin can.
›Challenge your friends to a contest. Who is the best shot?
Questions to think about
When is the potential energy the greatest?
When is the kinetic energy the greatest?
How does the mass of your projectile affect its flight?
What forces are acting on your projectile before you let go?
What forces are acting on your projectile once it’s fired?
Try This!
Try adding more rubber bands to your slingshot. How do more rubber bands affect the mechanical energy of the slingshot and projectile? What’s the farthest you can fire a projectile with your slingshot?
Consider This!
Using a slingshot can get pretty tiring for your hands, especially the one holding the tool. Some slingshots are designed with a brace that goes around the wrist of the hand holding the slingshot. This adds support and increases the amount of strength you can use to stretch that elastic back. How can you add wrist support to the slingshot you just made? How does this affect your shot?
Mangonels use tension and torsion to fling their projectiles great distances. But you don’t need a medieval army to build one for you—you can make your own at home!
Warning: Never point or fire a mangonel or any other weapon at a living creature. Always wear eye protection.
›Stack at least five craft sticks together. Tightly wrap both ends with rubber bands and set aside.
›Stack two craft sticks together. Tightly wrap one end with rubber bands.
›Carefully separate the stack of two craft sticks. Put the stack of five craft sticks between the two craft sticks.
›Slide the stack of five craft sticks close to the rubber-banded end of the two craft sticks. Wrap at least one rubber band around both stacks of craft sticks to secure them together.
›Glue and tape a plastic spoon to the end of the top craft stick. Place your projectile in the spoon.
›Push down on the top craft stick and release! You might need to hold your mangonel down. When you push down on the stick, you’re loading the mangonel with potential energy. When you let go, that potential energy becomes kinetic energy, sending the projectile on its way! The more potential energy you put into the catapult, the greater the kinetic energy—and the farther it will fly!
What kind of catapult is this?
What kind of potential energy does your catapult use?
What affects how far and how high you can catapult your projectile?
How accurate is your catapult?
What’s the highest your catapult can launch a projectile?
How would you measure it?
What’s the farthest your catapult can fire?
Consider This!
How can you change the launch angle of your catapult? What happens if you change the length of the throwing arm? Can you design a different or better catapult using the same materials?
Brutal Battle
During the Siege of Lisbon in the twelfth century, English crusaders attacked the Muslim city of Lisbon in the country of Portugal. The siege lasted four months and was successful at least partly because of the use of mangonels. It’s said that the English worked in teams of 100 men who used two mangonels to throw 5,000 rocks in 10 hours! Once the Muslims had surrendered, the terms dictated that the Crusaders would allow the people to keep their lives and possessions, but these terms were broken as the Crusaders entered the city and killed the inhabitants or drove them away.
Trebuchets use gravity to send their cargo flying. If you’ve got a castle to invade, it might be the siege weapon for you!
Warning: Never point or fire a trebuchet or any other weapon at a living creature. Always wear eye protection.
›First, build two A-shaped braces.
Cut one craft stick in half. Use two long sticks and one half-stick to make each A shape.
At the top of the A, the two long sticks should cross each other and make a small v. This is where the pencil will sit. Glue the craft sticks where they meet.
Repeat for the other brace.
Stand up one brace on the cardboard and mark where the legs are.
Cut slots into the cardboard to fit the legs of the brace. Use other craft sticks, glue, or tape to reinforce the brace on the cardboard.
Do the same for the other brace. The braces should be a few inches apart, wide enough that a pencil can rest across both of them.
›Then, build the arm.
Cut two small notches across from each other at one end of one craft stick. These should be wide enough to fit a piece of string.
Make a loop of string about 1 to 1½ inches long. Tape one end of the loop to a battery.
Hang the other end of the loop through the notches on the craft stick. Tape or glue the string to the notches.
Open one end of a paper clip to make a hook, leaving the rest of the paper clip flat.
Tape the flat part of the paper clip to the craft stick opposite the battery. The hook should point up and away from the battery.
Cut off a 1-inch piece of plastic straw. Using tape or rubber bands, attach the straw to the arm, perpendicular to it. The straw should be closer to the battery than the paper clip.
Slide the pencil through the straw and lay the pencil across the braces so it rests in the small v at the top.
Attach the pencil to the braces using tape or rubber bands. The arm should pivot around the straw.
›Finally, prepare the sling and payload.
Make a loop of string about 1 to 1½ inches long.
Use tape to attach your small projectile to the string.
Hang the loop on the paperclip hook.
›Fire your trebuchet! Pull down on your payload and release!
Questions to think about
What kind of potential energy is used by the trebuchet?
How is the potential energy turned into kinetic energy?
How does the sling affect the flight of the projectile?
What affects the launch angle of your payload?
What’s the farthest you can fling a projectile?
Try This!
Try counterweights other than the battery. How does the weight affect the flight of the projectile? What happens if you change the arm? Try moving the pivot point. What happens? What about making the arm longer or shorter?
Potential energy and kinetic energy are closely related. You can see the effects of both in this experiment.
›Turn a plastic or paper cup upside down and cut an opening at the lip big enough for your marbles to fit through.
›Place a cardboard tube at an angle, taping one end to the floor and one end to a sturdy object such as a table leg or a wall. Be sure that your marble can easily roll through the tube!
›Place the cup upside down at the bottom of the tube with the opening facing the tube so that the cup will catch the marble. Don’t tape the cup to floor.
›Place one marble at the top of the tube, and let it roll! How far does it move the cup? Measure and record the data in your engineering notebook. Do this several times with the same marble. Can you average the distance?
›Repeat the experiment with marbles or balls of different weights. Record how far each ball moves the cup.
Questions to think about
When is the marble’s potential energy the greatest?
When is the marble’s kinetic energy the greatest?
Which marble has the greatest potential energy?
Which marble has the greatest kinetic energy?
Where are the kinetic and potential energy equal?
How does the marble’s mass affect the movement of the cup?
Try This!
Change the height of the tube and repeat the experiment. How does it change the mechanical energy of the marble? How does it affect the motion of the cup?
energy skate park basics 1.1
