Why does a bicycle stay upright? | The physics behind stability of bicycle

Many people (almost all) from their childhood have always wondered why does a bicycle stay upright when moving? 

This is a very common but very interesting question.

 Today you'll understand the answer. 

And your search for the question:- " why does a bicycle stay upright" will end after reading this article.

Are you interested?

 First of all, let's understand 

What keeps a moving bicycle upright? 

So, there are two things that stabilise the bicycle:-

1. Bicycle must have enough speed.

2. Bicycle's handlebar (steering) must be turned in the direction of lean whenever the bicycle tends to lean.

(When the bicycle leans on the left side handlebars must be turned in the left direction and vice-versa.)

Why the bicycle must have some speed and its handlebar must be turned in the direction of lean?

To learn this, first, you should learn about the concept of the centre of gravity and the stability of any object because the bicycle stays upright only when it is stable.

And later you'll learn why does a bicycle stay upright?

What is the centre of gravity?

The Centre of gravity is an imaginary point in an object where the distribution of weight is equal in all directions, and it does depend on the gravitational field.

From this figure, I want to show you that 

w1+w2+w3+w4+w5+w6+.... = W 

It means the centre of gravity is a point from where all (resultant) gravitational force appears to act.

And the distribution of weight at that point is equal in all directions. 

What makes any object stable? The concept of stability.

A body will be stable if the line joining the centre of gravity of the object and the centre of the earth falls within the base of the body.

Have you ever balanced a pencil in your finger like in the given figure below?

In this game, when the pencil leans on the left side you move your finger on the left side and when to moves on the right side you also move your finger on the right side.

But why?

Because when pencil leans on the left side its centre of gravity also shifts towards the left.

And as you know for the stability of any object the line joining the centre of gravity of an object and earth must go through the base of the object.

 And when we move the tip of the pen left by moving our finger in the left direction, the pen's tip(base) comes below the centre of gravity keeping it stable.

 Just like that, when bicycles lean on the left side, it's centre of gravity also shifts left.

Thus, the bicycle must move in the left direction so that its wheel come under the centre of gravity.

And, to move the bicycle in the left direction, the steering's direction must be changed in the left and it also requires speed because without the speed bicycle will not be able to move in any direction it will just stay at a point.

That's why the bicycle's handlebar's direction must be changed in the direction of lean and it must also have enough speed.

Did you know that you have to move handlebars in the left direction went it leans left when you learned to ride bicycles for the first time? if not then who does this job?

It may be possible that you know that you have to paddle to balance.

 But did you know both things at the age when you learn to ride a bicycle? 

most probably not. isn't it?

 

Not only kids, but many adults also don't know these things but they are riding bicycles for years. 

             Then who changes the direction of handlebars in the direction of lean.

Do bicycles are capable of changing the direction of handlebars in the direction of lean themselves.

Are bicycles made by tony stark? 

Although these are not made by tony stark, yes it's the bicycles themselves who are capable of changing the direction of handlebars itself.

Does it mean that the moving bicycle will move forward, upright and balanced without a rider?

The answer is again yes, it will.

You can also check it.

    

                          Take your bicycle and push it forward with free handlebars i.e., handlebars must be free to move in any direction.

You can observe it more clearly if you will perform it on a slope. 

You'll observe that bicycle will move in the forward direction balanced and upright.

           

                If you are too lazy (like me) to do that experiment just watch the video below in which a bicycle keeps riding without a rider, just because of speed and its ability to turn to steer itself.

So, now you know that it's true.

 

But how?

What makes a bicycle change its handlebars itself? 

Which force keeps a bicycle upright?

The physics behind the stability of bicycles.

   Three things that keep the bicycle upright by changing the steering's direction in the direction of lean:-

1. How weight distribution of the front wheel and handlebar keeps the bicycle upright?

You can see in the above figure, the weight of the front wheel and handlebar is distributed in front of the steering axis.

So, whenever a bicycle leans in the left direction front portion of the front wheel tends to fall before the back portion because weight (force) is more in the front portion.

Since the front wheel's front portion falls in the left directly before the back portion, therefore handlebar's direction is also changed in the left.

2. How Caster effect keeps the bicycle upright? 

The bicycle's front wheel touches the ground slightly behind the steering axis.

So, when the bicycle leans in the left direction then the upward force from the ground pushes the wheel from the point from where it touches the ground.

Since the point from where the wheel touches the ground lie behind the steering axis, therefore wheel's back portion is pushed in the right direction and hence the direction of the front wheel gets changed to the left.

3. Why does a spinning wheel stay upright? | Gyroscopic effect of spinning front wheel.

Do you know what is a gyroscope? 

A gyroscope is a device consisting of a rotor that turns very quickly inside a frame and does not change its spin axis direction when the frame is moved in any direction.

Why gyroscope's rotor does not change its spin axis's direction?

Gyroscope's rotor does not change its spin axis direction because of the gyroscopic effect.

What is the gyroscopic effect?

Gyroscopic effect is a tendency of a rotating body to maintain its spinning axis direction.

Use of gyroscopic effect in bicycle

The wheels of the bicycle also act as a rotor of the gyroscope when it is rotating.

So, when we ride on bicycles It's a wheel that is rotating and due to the gyroscopic effect, it stabilised the bicycle. Thus making the bicycle stable.

Note:- All three things are not necessary to make a bicycle stay upright.

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