In This Issue:

• Amusement Park Rides & Physics
• Centripetal Force Project
• Make a Roller Coaster
• Inventions: Roller Coaster Loops
• Fabulous Facts
• Science Links

Amusement parks are thrilling places to spend the long days of summer, but did you know that these parks are also huge physics classrooms? All of the rides are built with the laws of physics in mind, and it is playing with these laws that makes these rides so fun and scary. We'll take a look at four of the most common types of rides to see how the forces, energy types, and laws of physics are at work in amusement parks.

Bumper Cars: Newton's Three Laws of Motion

Bumper cars are a great place to see Sir Isaac Newton's three laws of motion in action. Here's how:

Newton's First Law: Every object in motion continues in motion and every object at rest continues to be at rest unless an outside force acts upon it. This is because all objects have inertia - the property of matter that resists changes to the object's motion. Newton found that if a ball is sitting on a table, it will stay sitting there because that is what it "wants" to do. If the ball is set in motion, it will keep traveling in a straight path because, again, that is what it "wants" to do. An object in motion will not stop, slow down, or change its direction unless an outside force acts on it (such as gravity, friction, and air resistance). When you are riding in a bumper car and end up in a collision with another bumper car, you feel a jolt. This is because your body's inertia wants it to keep traveling in the direction it was moving with the car even though your bumper car has now suddenly stopped.

Newton's Second Law: The greater the mass of an object, the harder it is to change its speed. (More force is needed to move it.) You already know this law and practice it in your everyday life. Something that is small, such as a pebble, is much easier to pick up and throw than something that is large and heavy, such as a boulder. When riding in the bumper cars, you may have noticed that people who weigh less tend to get pushed around more than people who weigh more. The more mass (weight) an object has, the more force it takes to move it. And since all the bumper cars usually have the same top velocity, the cars carrying more mass will never travel as far as the cars carrying less mass after a collision.

Newton's Third Law: For every action, there is an equal and opposite reaction. If two bumper cars traveling at the same speed and carrying the same amount of weight run into each other, they will bounce off and move an equal distance away from each other. And based on the second law, if there is a difference in the amount of weight being carried in the two cars, the car with less weight will travel farther away from the point of impact than the car carrying more weight.

Click to learn more about Newton's Three Laws of Motion.

Carousel: Centripetal Force

Imagine spinning a ball on a string around you. The ball is traveling in a circular path. But Newton's first law states that an object in motion stays in motion and that motion is in a straight path, not a circular path. Since the ball is traveling in a circular path, an outside force must be acting on the ball - that force is the string. The string is pulling the ball back toward you, acting as the centripetal force.

Centripetal means "center-seeking" and is the force that is acting on the carousel. The platform upon which the horses and people are riding is the centripetal force that keeps them traveling in a circular motion just as the string was the centripetal force for the ball. As long as the ride is moving slowly enough, the centripetal force of the platform can keep everyone and everything on board. In theory, if the carousel starts moving really fast, centrifugal force* ("center-fearing") takes over and breaks the hold the platform (centripetal force) had on the riders and the riders would fly off.

*Centrifugal force is actually not a real force. If the centripetal force that pulls an object into the center stops working (e.g. the string breaks), then it is the object's inertia that takes over and sends the object traveling in a straight path. You can test this outside by spinning a ball around you and letting go of the string. If centrifugal force was a real force, the ball would move straight away from the center at the point where the string was let go. But it doesn't. Instead, the ball follows its path of inertia and moves in a straight path that is tangent to the circular path.

Free Fall: Potential Energy, Kinetic Energy, and Gravity

In free fall rides, motors are used to take the car and the passengers to the top of a tower, building potential energy as they reach the top. Potential energy is stored energy and has the capability to become working energy. When the car is released, the potential energy is turned into kinetic energy (the energy of motion) as gravity pulls the car and passengers back down to the earth. However, no matter what an object weighs, all objects fall at the same rate*. So both you and the car are falling at the same speed, giving you the feeling of weightlessness.

Now you may be "fooled" into thinking that the car is falling faster than it normally would if gravity was the only acting force (i.e. the ride makers are using motors to make the car fall faster). After all, you did see and feel yourself being pressed up against the bars and straps holding you in as soon as the car dropped. But remember that your body has inertia and wants to stay at rest, as does the car you are sitting in. The mechanism suspending the car at the top of the tower is holding the car, not you. The car is holding you. So when the mechanism that is suspending the car lets go, there is a slight delay of your body falling with the car because your body's inertia wants to keep it at rest. If the same mechanism dropped you and the car at the same time, there would be no delay of your body falling in comparison with the car.

*Although all objects do fall at the same rate no matter what their weight or size, some objects are more likely to be affected by air resistance than other objects. Because of their spherical shape, balls allow air to easily move past them, with little air resistance to slow them down. Feathers and parachutes are shaped to capture the air as they fall to the ground, effectively slowing them down. In a vacuum, all objects always fall at the same speed since there is no effect of air resistance.

Roller Coaster: Putting It All Together

Roller coasters are the perfect place to see all these laws, forces, and energies at work! Roller coasters are not powered by motors the entire way along the ride. In fact, most roller coasters are only pulled up to the top of the first hill - the highest point of the entire ride. Its entire trip relies solely on the potential energy it has gained by its position at the top of this hill. The higher a roller coaster climbs a hill, the greater a distance there is for gravity to pull it down. When the roller coaster comes down the hill, its potential energy is converted into kinetic energy. When the coaster moves down a hill and starts its way up a new hill, the kinetic energy changes back to potential energy until it is released again when the coaster travels down the hill it just climbed. To see how potential and kinetic energy are built up and released, click here.

Gravity and inertia are big players when it comes to how you experience the ride. The force of gravity is measured in g-forces. Most of the time, you are experiencing 1 g, the normal force gravity exerts on you. However, motion can change how you experience the force of gravity. When the cars are traveling up the hills, you feel heavier because your inertia wants you to stay behind and more g-forces are exerted on you. So, if a ride states that it exerts 3 g-forces, then you will feel like you weigh 3 times more than you really do while riding on the ride. Alternatively, when the car travels down the hills, you feel weightless because you are falling with the car and are experiencing 0 g-forces.

When loops and twists are built in the track, the track becomes the centripetal force that keeps the cars and passengers moving in a circular motion. The inertia of the passengers, which wants them to travel in a straight line, makes the passengers feel like they are being "pressed" into their seats while traveling through the loop. When a coaster goes up a loop or hill, it must come down, because for every action, there is an equal and opposite reaction. And if there is not enough force or speed to overcome its mass, a roller coaster cannot make its way through the entire course of its track.

Science Project: Centripetal Force

It's not magic that keeps people in roller coaster cars that travel in looping, spiraling paths - it's physics. Try this experiment to see how centripetal force and inertia keep people inside cars even when traveling upside down.

Materials:

• Small plastic bucket
• Water
• Sturdy string
• Outdoor place that is OK to get wet

What to Do:

1. Tie the string securely around the handle of a plastic bucket. Use a plastic bucket rather than metal so it is not heavy.
2. Pour a glass full of water into the bucket. (Again, don't add too much water so it is not too heavy.)
3. Hold the string so that the bucket is about level with your knees. Adjust length of string as needed.
4. Spin the bucket of water over your head in a vertical (up and down) direction. Make sure you spin the bucket fast enough so it stays in a circular path. Does the water spill out?

What's Happening?

It seems as if the water in the bucket is defying gravity, but is it really? No. Gravity - the force pulling down on everything - is still at work even when the bucket and water are above your head. The water's inertia wants to keep the water traveling in a straight path, but gravity is acting on the water, causing it to fall in a downward path that will eventually hit the earth. However, while the water is falling, the bucket is falling with it, catching the water. What keeps the bucket and water moving in a nice circular path that doesn't get wet or messy is the string. The string acts as the centripetal force that pulls the bucket and water into the center and keeps them from following their paths of inertia, giving the illusion that centrifugal force is pulling the water away from the center. But be careful. In order for the bucket to keep falling with the water, the bucket must travel fast enough to keep up with the water. If you spin the bucket too slowly, the water will fall out and you will get wet.

Science Project: Make a Roller Coaster

Test your knowledge of physics by making your own roller coaster. You can make a roller coaster out of just about anything, but below you'll find a list of materials to use as cars, to make tracks, to support your tracks, and to make hills. You may find some materials work better together than other materials, especially depending on the size of your track and cars.

Materials: This table gives you a list of suggested materials to use as cars, tracks, adhesives, and supports to make your roller coaster. You will not use all of these items, but hopefully this can help you make your roller coaster with items you already have and/or can easily obtain.

CARS	TRACKS	ADHESIVES	SUPPORT
Marbles	Vinyl tubing	Tape	Staircase
Ball bearings	Poster board	Glue	Books
Metal B-Bs	Cereal boxes	Clay	Chairs
	Cups	Staples	Bed
	Foam insulation tubes		Wood blocks
	Cardboard tubes

What to Do:

1. Spherical objects such as marbles and ball bearings tend to make the best "cars" for your roller coaster. The size of the marbles/balls needed depends on the type of material you use for your tracks. For instance, while vinyl tubing works well to make tracks that bend and curve, only small objects like B-Bs and ball bearings can actually fit in most vinyl tubing. However, vinyl tubing is probably the easiest material to make tracks with, so we recommend using it for your first attempt at making a roller coaster. Most hardware stores carry vinyl tubing in a variety of sizes, so test your cars to make sure they can move through it before you purchase it.
2. If you use poster board or cereal boxes, cut out long strips to make your track. You may have to build walls or sides to keep your car from falling off.
3. Whatever material you use, build your track so that the cars can run smoothly on it - no cracks or seams that will trip up the cars.
4. Use the adhesives to connect track pieces together as well as connect the track to your support system.
5. Remember the laws and forces of motion when building your roller coaster track. Your first hill must be the tallest to build up enough potential energy to get your car through the track. Adjust hills and loops so that the car will have enough velocity to make it through the course without having so much speed that it flies off.
6. You may want to try several different cars with different sizes and weights to see which car moves through your track the best.

What's Happening?

You may find it very tricky to build the track just right so that the car can make it all the way through without falling off. Ride makers of roller coasters face these same challenges: how to make a fun, thrilling ride that is also safe. But by following the laws of physics, ride creators can make rides both fun and safe without a lot of trial and error, which is a good thing for the riders!

Inventions: Roller Coaster Loop

Throughout most of their history, roller coasters have been very popular. Ride makers have always looked for ways to make the next roller coaster more thrilling and more unique than the ones before it. Steep drops, switchback tracks, and scenic rides with music are just some of the ways ride makers make their roller coasters more fun and appealing to riders. But probably the most exciting aspect of any roller coaster is the vertical loop, even though this was one of the last features of the roller coaster to be successfully achieved.

Roller coasters have a long history, dating back to 1400s Russia when the coaster hills were made of ice. France picked up on this thrilling ride in the 1600s, and in the 1840s the first ever vertical looping coaster was built. Called the Centrifuge Railway, the loop on this ride depended solely on centripetal force and inertia to hold the cart on the track and the riders in the cart. Obviously, this design was not very safe and, after one accident, the government shut the ride down.

In 1895, the vertical looping roller coaster was tried again, this time at Coney Island in America. Known as the Flip Flap Railway, it featured a perfect circle in its track. While this design sounds safe and simple enough, it was actually very dangerous. The descending track of the circular loop caused the passengers to undergo 12 g of force (the most extreme and strenuous rides of today only exert 4 or 5 g on the body). To make matters worse, the car on the Flip Flap Railway was often described as a "box on wheels," meaning it had none of the straps, belts, or cushioned seats of today's cars, making for a very jostling ride. The ride closed after only a few years of operation due to serious whiplash injuries and people being afraid to ride it.

To counter this design flaw, Edward Prescott made the first clothoid loop roller coaster in 1901, known as the Loop-the-Loop. Rather than the vertical loop being built in a perfect circle, it was designed to have a tear-drop or elliptical shape. This is the same loop design that is used in today's roller coasters. This change in design drastically cut down the amount of force exerted on the passengers, making it much safer and more comfortable to ride. Unfortunately, too many people remembered the Flip Flap Railway and the pain it caused and were afraid to ride the Loop-the-Loop. Due to more people wanting to watch the ride than ride it, the Loop-the-Loop shut down in 1910.

It wasn't until 1976 that the vertical looping roller coaster design was tried again. A designer named Anton Schwarzkopf was asked by Magic Mountain (later named Six Flags Magic Mountain) to design a looping roller coaster. By making the loop more elliptical in shape than its predecessors, thereby lessening the force experienced by the riders, Schwarzkopf successfully designed the Great American Revolution, the first modern roller coaster to feature a vertical loop. Of course, it probably also helped that none of the riders in 1976 remembered the Flip Flap Railway.

Fabulous Facts

Safer than you think? The shoulder straps on most loop roller coasters serve no other purpose than to make you feel safe. What really keeps you in the seat of the coaster is the centripetal force acting on you when going around the loop, pushing you into your seat. In fact, you may actually feel like you are in an upright or standing position even though you really are upside down.

Wow, that's big! The first Ferris Wheel was built in 1893 by engineer George W. Ferris. Designed to rival the Eiffel Tower that was unveiled in 1889, the Ferris Wheel was 264 feet tall (as tall as a 26 story building) and each gondola (the cars where the passengers rode) could hold forty people. (That's the size of a bus.) There were 36 gondolas on the ride, meaning that 1,440 passengers could ride the Ferris Wheel at one time!

Science Links

Put what you learned about physics to work! Adjust the shape of the hills, speed, gravity, friction, and mass of the roller coaster to see how these forces and energies can work together to make a fun ride or a crashing mess.

Learn more about the physics of falling, floating, and turning. This site includes animations, science projects, and videos to help demonstrate the concepts and forces being applied at each of these thrilling rides.

This roller coaster simulation shows the forces and energies at work as the car makes its way through the roller coaster loop.

Try your hand at designing a roller coaster and then test it out to see how well your design worked. There are three different angles available to view the test run of your tracks, so see if your design was a success or a flop.