My Project:

When we started doing this project I had absolutely no idea what to do for it.  I finally decided to do something I love: take pictures.  I don't love riding bikes, but it is a fun activity so I decided to explore the physics in bicycles by taking pictures of them.  I've loved it.  I've learned to look at bicycles differently and I've learned a little bit more about how they work.  I hope as you look at my blog and see the work I put in it, that you can appreciate the pictures and the physics in bicycles as well. Enjoy!

Wheels

Wheels are a very important part to a bicycle.  Without the cornering force and camber thrust on the bike, it would be impossible to move or balance. On a normal bike there are two wheels: the front and the back.  There is a torque applied on the tires that is called the yaw torque.  It happens on the front wheel and is caused by two opposite torques:

• The self-aligning torque: asymmetric forces that occurs behind the geometric center of a contact path.  It happens on the front wheel away from the direction the bike turns.  This makes the radius of the turn bigger.
• Torque that is focused towards the direction the bike turns.  It is caused by the bike turning and the contact path during that turn.  Since it happens toward the side the bike turns, the radius gets smaller.

This is an example of a contact path during a right hand turn:

Balance

Balance in a bicycle is created by a number a factors.  The handlebars, pedals, tires, and rider all work together to keep the rider upright and balanced.  In order for the bike to stay balanced, the reaction forces have to be exactly equal to the forces applied by the bike.  Wikipedia uses the examples of gravitational if leaning, inertial or centrifugal if in a turn, gyroscopic if being steered, and aerodynamic if in a crosswind.  The balance depends on the geometry, mass distribution, and forward speed of the bike, and weight of the rider.  These will all influence how easy or hard it is for the bike to actually stay upright.

Handlebars

The handlebars (along with the front tire and rider of the bike) help steer the bicycle.  The steering angle of the bicycle is caused by the rotating steering axis.  Wikipedia has the equation for the actual kinematic steering angle: 

( is the kinematic steering angle,   is the actual steering angle, and   is the caster angle of the steering angle.)

Steering the bike is an important part of the bike because it helps the rider stay upright and get where they need to go.

Steering a Bicycle

When someone steers a bicycle different parts of the bike are being used.  The steering wheel, the tires, the traction from the bike and road, and the speed of the bike.  Motion is a major part of the physics in steering. Then as you steer the bicycle the rate of the speed of the bike affects how much you need to steer it.  The types of bike can also affect just how much the bike needs to be steered.

Seat (Saddle)

The seat may look like a small, unimportant part of a bike, but it actually does have some importance.  The way it is shaped and positioned does affect the bike.  Different bikes have different shapes of saddles.  For example, racing bikes, triathlon bikes, and mountain bikes all have different positions and shapes of a saddle because they are used for different things.  Don't underestimate the power of the saddle because it can also make your biking experience very comfortable or very uncomfortable.

Gears

Gears are simple machines.  They're the "wheel and axle."  They are used to transfer motion and movement in the bicycle.  Some bikes have very complex gears and some have very simple gears, it just depends on the bike.  But they are very important part of the bike, allowing it to go at different speeds depending on where they are riding the bike.

Pedals

The Pedals on a bike are part of a simple machine: wheels and axles.  They are what move the tires on the bike.  Without them, there would be no motion on the bike.  The rider applies force onto the tires which in turn move the bike.

Brakes

The brakes applied on the bike create friction.  They are very important to help the bike stop.  There is also inertia applied to the bike when the brakes are applied to the bike.  The bike doesn't stop immediately, it takes a few seconds for the bike to completely stop.

Force in Bicycles

The two forces applied to bikes are external and internal forces.

• Internal forces are applied by the rider of the bicycle or the friction.  The rider applies the force through steering the bike.  It happens in the handlebars, wheel, and pedals.  It is generally a torque that is applied.  The friction is caused in many different areas: from the ground, the gears, the brakes, and the pedals.
• External forces are applied from gravity.  The pull of gravity causes the external force of the bike. There is the riding resistance the ground creates, the air-resistance and drag the air creates, and force from braking.

References

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

http://en.wikipedia.org/wiki/Bicycle_saddle

http://www.ceeo.tufts.edu/robolabatceeo/K12/classroom/gears.shtml

Physics Summary

So as you can see, there are many different factors that affect physics in bicycles. It was hard to figure out what parts of the physics I wanted to cover.  So just a little review:

• The Handlebars are a very important part of the bicycle making it able to be steered by the rider.  The physics involved are motion and steering angle.
• The gears are a simple machine (wheels and axles) that allow the bike to go at different speeds.  They also have motion involved along with torque and speed.
• The tires make the bike move and help with steering the bicycle.  They also make the bike turn.  Physics in tires include torque, motion, and friction.
• Internal forces and external forces are applied to bicycles through gravity, friction, the rider, brakes, steering, etc.