BIKES: Science on Two Wheels

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Educational Resources

Science Concepts & Content

Forces & Motion
Cycling is all about motion, preferably forward and not downward. All bicycles must overcome the force of gravity, which can make the rider fall and causes friction with the road surface. The main physics concept in cycling is momentum, which is mass x velocity. The more momentum an object has, the more energy is required to change its motion. When a rider is moving slowly, it is quite easy for unbalanced forces to tip the bicycle over. At faster speeds the rider has more momentum, which makes balancing easier. In addition to momentum, understanding the center of mass is critical in knowing how a bicycle works. The center of mass must remain over the bicycle’s frame to continue in a straight line. To turn a bicycle, countersteering and leaning are employed to displace the center of mass. While traveling at speed, turning the handlebars slightly to the left will displace the center of mass to the right. The rider controls this displacement by leaning into the turn and turning the handlebars back to the right. Once you learn how to ride a bicycle, these movements become reflexive and you don’t even realize you’re doing it.

In physics, energy is the ability to do work. Energy can come in many forms. It can be stored as potential energy, such as the energy locked away in chemical bonds, or kinetic energy, like wind. Energy can be neither created nor destroyed, but it can be converted from one form to another. In cycling, the work being done is moving the rider from one point to another. In order to do this work, the cyclist rotates the pedals (kinetic energy) which drives the chain, which rotates the sprocket attached to the rear wheel, which causes the wheel to spin. The spinning of the rear wheel pushes backward against the ground, and the bike is propelled forward as an equal (but opposite!) reaction to this backward push. When it is time to stop the brake pads rub against the wheel rim; this friction converts the kinetic energy of the wheel to heat, which decreases the speed of the bike until it comes to a complete stop.

Technology & Engineering Systems
Modern high-tech bikes still share their basic design with the “safety” bicycle of the 1890’s. Carbon fiber frames, disc brakes, Shimano shifters, Kevlar mountain bike tires, aerodynamic helmets, rust-proof powder coats, and everything else on a bicycle has been improved over the years. What advances will happen in the next 20-50 years? We can’t say for sure, but those machines will still be instantly recognizable as bicycles.

Effects of humans
Bicycles have positive impacts on human health and environmental health. Exercise, such as cycling, has positive physical and psychological benefits. The most notable environmental effect of cycling is the absence of pollution; no greenhouse gasses or carcinogens are produced by riding a bicycle, and the environmental cost in materials and pollution of building a bicycle are far lower than for automobiles.

History of Technology
Invented in the last half of the 19th century, the bicycle has been seen its share of technological advances. The earliest models lacked pedals altogether; the rider strode to gain speed then coasted. Pedals were first used to turn the front wheel, and the front wheels were made larger to provide more speed until bicycles morphed into the penny-farthing variety. When the inherent danger of these contraptions was realized, bicycles were again made with two equally-sized wheels. Adding a sprocket and chain assembly to the rear wheel and pedals allowed for greater speeds with smaller wheels, and the development of derailleurs in the 1920’s allowed bicycles to change gears for greater efficiency. Modern materials, like aluminum, titanium, and carbon, have all seen use in bicycles. Mountain bikes employ sophisticated suspension systems to provide a smoother ride.

Being a worldwide icon, bicycles have long been an outlet for creative design. Bike builders have experimented with materials such as bamboo, wood, and steel to create unique designs that are as striking as they are functional. Some types of bicycles, like fixed-gear bikes (or “fixies”), are identified with subsets of riders – in this case bike messengers and hip urban youth. The west coast “bling” bikes express the individuality and creativity of their riders. Even bicycle accessories like fenders and saddle bags marry form with function to provide riders with the exact style they are looking for.

Science Content for Each Interactive

Gyroscope Seat
Inertia is the property of matter which causes an object to resist changes in its movement (Newton’s First Law): an object at rest stays at rest, an object in motion stays in motion, unless acted upon by an outside force. We usually think of this linearly, but the same is true of objects that are spinning. Rotational inertia is the property of spinning objects that makes it difficult to change the axis of rotation; the faster a wheel is spinning, the harder it is to tip over. When you tilt the bike wheel while sitting on the rotating seat, you are spun around by the equal (and opposite!) reaction of the wheel pushing back to resist the tilt.

Gear Table
Gears transfer energy from one point to another to do work. Using a large gear to spin a smaller gear allows you to do more work with the same effort as using equally-sized gears. Bicycles use gears to help build speed and climb hills.

Helmet Aerodynamics (Drag Race Exhibit)
While bicycle racers ultimately rely on the conditioning of their legs and lungs to win races, it is important to reduce the amount of air resistance they encounter. Racers lean forward, use special handlebars, and wear tight-fitting clothing all in an effort to reduce air resistance. Another helpful tool in the fight against air resistance is the teardrop-shaped helmet. The shape of these helmets is engineered to improve aerodynamics, much like jet planes and race cars, to give speedsters the greatest efficiency possible.

Roller Ramps
Imagine rolling a wheel from a higher point to a lower point. A straight line is the shortest path between the two points, but what is the fastest path between the two points? This question was first posed in 1696 by Johann Bernoulli, who discovered that the solution to this question was a cycloid curve. A cycloid is the curve made by tracing the path made by a point on a circle as it is rolled across a surface.

Coatings/Color Match
Many people think that eyewitness accounts are the strongest evidence available to a court of law, but the truth is that we don’t remember very well everything we see. Compare the different shades of red; which one is the shade of red used on stop signs? Our inability to correctly remember such a detail can be astounding.

Tire Treads
Bicycle tires come in many different styles, from slick racing tires to knobby mountain bike tires. The tire tread, along with the width of the tire, affects the way a bicycle handles different terrain. Visitors make a rubbing of different tire treads to see the surface area of the tire that actually touches the ground.

Bike Body Xylophone
Bicycle frames have been made of many materials over the years. Wood, cast iron, steel, aluminum, and composite materials have all seen use in bicycles. Technology has also allowed us to use thinner and thinner metal tubes, and tubes of different shapes, to make bicycle frames. When you strike each material you will hear a different sound.

Bike Seat Bench
Which is more comfortable – a soft, squishy seat or a firm, hard one? In cycling parlance, standard bicycles have a saddle rather than a seat. A seat (like on a recumbent bicycle) is designed to bear the full weight of a sitting person, but a bike saddle only needs to support part of the rider’s weight (the rest is supported by the legs and arms). On short rides a squishy gel saddle can be markedly more comfortable than a hard one, but over long distances they can actually cause chafing of the thighs. That is why most distance riders will opt for a hard plastic or leather saddle.

Color Mixing Bike
For many people, bicycles are more than efficient transportation - they are an extension of the individual’s style. Bicycles are available in a wide array of color schemes, from sleek one-color racers to wild multi-colored mountain bikes. Shine red, green, and blue lights on a bicycle to make it any color you want. By varying the intensity of the three lights you can make almost any color imaginable.

Bicycle brakes work by using friction to convert the kinetic energy of the wheels into heat. The most common types of brakes are rim brakes, disc brakes, and drum brakes. Different materials have been used in the brake pads over the years, including rubber, wood, cork, and brass.

Carbon/Steel Scales
Bicycles have embraced technological advances ever since the first bike was produced. For most of the twentieth century bicycles were made from steel tubes, but advances in material science provided us with composite materials that provide the same (or greater) strength with lower weight. Many racing bicycles today are built using carbon fiber composite materials.

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