Pedaling Through the Parts
HOW BICYCLES WORK

Have you ever gotten on your bicycle and wondered how it works? Bikes are really a bunch of simple machines that work together. Wheels, pedals, gears, and brakes are all simple machines. Click here to learn more about the simple machines in a bike. If you'd like to know more about a mountain bike's suspension, click here!

If you want to understand how bicycles work, you also need to know a little bit about physics. Bicycles obey the laws of physics. The laws of physics that you should know to be able to understand more about your bike are force and motion, gravity, inertia, and friction.

 Force & Motion Gravity Inertia Friction

FORCE AND MOTION

A force makes things move, but a force can also stop things from moving. When you pedal a bike, you use your muscles to create a force. You are like the engine for your bike. You push the pedals in a circle to start a forward motion.

When you squeeze the hand brakes, you are also exerting a force which stops the motion of your bike. Motion is another name for movement. Speeding motion up is called acceleration. Slowing down motion is called deceleration.

GRAVITY

Do you remember when you first got on a bike? You probably fell a lot. The reason you fell is because you were too young to make the wheels go fast enough to keep the bike going in a forward motion, so gravity pulled you down. (In inertia, you will learn why forward motion is so important.) When you became older, you learned how to make the wheels go fast enough, so you could stay up.

When you make the wheels go fast enough, the wheels create a force that acts as an anti-gravity force. A bike works like a gyroscope. A gyroscope is a cool thing that defies gravity. By putting a string around the axle and pulling hard, you make it spin very fast. So basically, when you are riding your bike, you're defying gravity!

Here are pictures of a gyroscope still and spinning. Cool!

FRICTION

Friction slows things down. Friction also tries to stop one surface from sliding on another. If you were trying to ride your bike on an icy road, there would not be enough friction between the surface of the tires and the surface of the ice. You would slide and not have control of your bike.

Another way friction has to do with bikes is in the parts of a bike. For example, if you want less friction on your bike, put oil on the chain and gears, so you don't have so much friction to slow you down. The oil helps your gears turn easier, and that helps keep gears from wearing out.

You can feel friction when you rub your hands together and they get warm. Now put soap on your hands and rub them together. Do your hands move easier with soap? That's like putting oil on gears!

INERTIA

According to Newton's First Law, inertia is the tendency for an object that is moving to keep moving and the tendency for an object that is at rest to stay at rest.

To prove that inertia exists, go outside and pedal your bike fast and then brake. Did you stop immediately? Or did you skid a little bit? Because of inertia, you should have skid a few inches.

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