November 16

Do pencils need friction to write? The Physics of Pencil Drawing

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When drawing with a pencil, do you feel the need to press down on the paper for it to work? If so, you are not alone. Many people believe that a lot of friction is needed for writing to happen. However, this isn’t true! The writing process actually works through sliding friction, so moving the pencil lead is the essential process. What does this mean? When drawing with a pencil or any other writing device, there needs to be sliding friction between the molecules at the pencil tip and the paper surface for anything to happen.

What is friction?

Friction simply is the force that opposes motion. For example, in writing with a pencil, the writing pen wants to move across the paper. Still, because of all of its contact points (the little bumps and grooves along your writing surface, when you look closely), it cannot do so without pushing through some sort of cohesion.

What Are The Four Types of Friction

Friction is the force that opposes motion. This means that whenever any two or more surfaces are in contact, friction can occur. There are four types of friction: static friction, sliding friction, rolling friction, and fluid friction. 

The first three types of friction, sliding and rolling friction, occur only with solid objects and surfaces. 

Fluid friction, however, occurs, as you might guess, in liquids and gases.

For more details on each type of friction, keep reading.

First Type of Friction; Static

Static friction acts when two or more objects’ surfaces are resting surface to surface. Say you are walking along a street, there is static friction between your shoes and the slabs each time your foot touches. If there was no static friction, the soles of your shoes would slip away from you, making it like to walk on ice. In fact, that’s what happens when you walk on ice because ice is very slippery and offers very little friction.
What other examples of static friction are there?
Another example is the friction that allows people to climb a climbing wall. It is static friction that keeps their hands and feet from slipping off the hand and footholds, allowing them to climb.

Second Type of Friction; Sliding 

When an object, say your sofa, needs to be moved, it’s Sliding friction that acts on the objects (your sofa) when they are sliding over the surface of the floor. One thing to know is that Sliding friction is a weaker force than static friction, which it’s way easier to slide a piece of furniture over the floor once it is moving than it is to start it moving at first. 

Sliding friction can be helpful as it is the core of this post; when you write with a pencil, you use sliding friction to deliver the “lead” to the paper. So as the pencil “lead” slides over the piece of paper (as you are writing or drawing), there’s just enough friction between the pencil and paper to leave a mark.

Another example would be riding a bike when sliding friction allows the brake pads and bike rims to work whenever you use the bike’s brakes to slow or stop. The friction slows the rolling wheels so you can stop, else the wheels would keep turning!

Next, Rolling Friction

When friction acts on objects when they are moving over a surface that is Rolling friction. Rolling friction is a lot weaker than sliding friction or static friction, which explains why most forms of ground transportation use wheels. So bicycles, cars, trucks, roller skates, scooters, and skateboards are all using rolling friction. Ball bearings are another use of rolling friction, where they let parts of a wheel or other machine roll rather than rub against one another.
Ball bearings in a wheel reduce friction when it turns.

And finally; Fluid Friction

Fluid friction is friction that reacts on objects that are moving through liquids or gases. So fluid is anything that can flow and take the shape of its container. Therefore fluids can be liquids or gases which can flow around an object. Have you ever tried to push your open hand through the water in a bath or pool, what you are feeling then is experiencing fluid friction. You can feel the way the water “pushes back” against your hand, that is the resistance of the water against your hand. Likewise, a skydiver falling toward Earth with a parachute is the air’s resistance against the parachute that slows their descent. 

The faster or larger a moving object is, the greater is the fluid friction resisting its motion. That’s why there is greater air resistance against the parachute than the skydiver’s body.

So The Summary Of Friction & Drawing with Pencils is

  • Friction is the force that opposes motion between any surfaces that are in contact. There are four types of friction: static, sliding, rolling, and fluid friction.
  • Static, sliding and rolling friction occur between solid surfaces. Static friction is strongest, followed by sliding friction, and then rolling friction, which is weakest.
  • Fluid friction occurs in fluids, which are liquids or gases.

What are the disadvantages of friction?

Well, the main disadvantages of friction are:

  • Friction produces a lot of heat. So the usage of machinery leads to the waste of energy as heat.
  • More energy is needed to overcome friction therefore making movement less effecient.
  • Noise production in moving parts leads to energy loss.

What are the advantages of friction?

  • Friction enables us to walk freely.
  • It helps to support the ladder against the wall.
  • Breaks of vehicles work due to friction.

What is cohesion?

Cohesion refers to adhesive forces between molecules within substances. For example, writing does require friction, and it does require cohesive intermolecular forces (cohesion) between writing utensils and writing surfaces.

Writing devices such as pencils have been designed to reduce the amount of friction they cause because writing is done through adhesive forces, which means that writing does not require rubbing! In addition, cohesive intermolecular forces allow writing devices such as pencils to interact with writing surfaces, and writing utensils such as pencils have been designed specifically for writing purposes.

What does writing with a pencil feel like?

Writing with a pencil is very smooth and easy because writing devices such as pencils are designed to reduce friction between the writing surface and their tips (erasers do the exact opposite). For example, graphite in your number two pencil has been ground down to avoid sharp edges in contact with the paper. This is why writing pencils are better for writing than knives or rocks – writing devices have been redesigned over hundreds of years to reduce friction when writing!

What about erasers? Do they need friction too?

No! Erasers increase friction because they are designed to grip writing surfaces. For example, when writing with a pencil, you use an eraser to lift up the graphite from the paper and onto your rubber or vice versa. This is why it is much easier to erase something that has been written in pencil as opposed to pen – pens have very little writing surface friction where writing utensils such as pencils have a lot of writing.

Can you use a pencil in a vacuum?

Writing doesn’t require friction, and writing devices such as pencils have been designed to reduce the amount of friction they cause when writing. However, writing does require adhesion (cohesive intermolecular forces) between writing utensils and writing surfaces! This means that you could write in a vacuum as long as an adhesive substance was lining your writing surface.

So can you write with a pencil in space?

Yes!

Can writing devices such as pencils be used in space? Yes, writing can happen through friction so pencils can touch the paper. However, they still cause some friction when writing because writing is done by pushing molecules together (adhesive forces), not pulling them apart as you might expect. In writing, pencils have been designed specifically to reduce the amount of friction they cause when writing. Therefore, writing devices such as pencils are better for writing long texts without damaging your writing surface!


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