If you’ve ever seen a shiny floor, chances are you’ve tried to slide on it. So why is it that we can slide on smooth floor boards but not carpet?
The answer is friction
Drag Force and Friction
Almost everything on this earth creates some form of friction.
If you ran your finger over a pin, you’d probably think it’s smooth, but zoom in and you’ll see bumps and grooves all over it (to the right is an electron microscope image of a pin head).
Friction occurs when objects rub together. Whether your on the ground, in the air or in water, you experience friction.
When molecules in the air push against and object, it causes friction.
If there was no friction you would swim further and faster, with much less effort.
You wouldn’t be able to walk anywhere because you’d constantly be slipping.
The breaks on your car and bike wouldn’t work.
So what is friction?
Friction is the force which acts in the opposite direction to motion. Different surfaces have different amounts of frictional force.
There are many different types of friction. Here, we’ll talk about
Fluid Friction
Sliding Motion
Rolling Motion
Sliding friction
As you can probably tell by the name, this form of friction occurs when we slide something, like a book across a table. When the book slides across, the bottom of the book is touching the desk.
The weight of the object and type of surface it moves on, determines the amount of sliding friction. The heavier the book, the more sliding friction.
Rolling friction
When an object rolls over a surface the force needed to overcome rolling friction is much less than that needed to over come sliding friction.
Essentially, you need less energy too roll something than slide something.
This is why you can push a car, even though it ways more than half a ton.
Fluid Friction
When moving through a gas (air) or liquid (water), there is some from of friction. This is called fluid friction.
Observe the animation to the left, in both cases fluid friction is pushing up and slowing the fall. This is because, as the objects fall water molecules push against it, generating friction.
However you an see the more, stream line one drops faster, as there is less friction acting on it.
So, how can we reduce friction?
One way is to use oil or grease. This method is called Lubrication. When you lubricate your bike chain the surfaces move past each other more easily.
This is why things may slip out of your hands when they are oily.
Friction partly causes drag. Air resistance and water resistance are Drag forces.
When an object moves through a fluid medium, it bumps into particles. The more particles it bumps into, the slower it becomes and the more drag it creates.
We use drag force to slow objects down. Sky divers and race cars use parachutes to slow themselves down.
Contact with the air creates a drag force, slowing the object down.
Reducing drag -
You may have heard of this or seen it before. Riders will often ride very closely behind each other in a straight line. The reason for this is so the people behind the first person use less energy.
Question
Short Answer Questions
1. Define Friction
2. Explain how friction is useful in every day life
3. How do states of matter affect drag (4 marks)
4. What is water resistance?
5. Copy and complete the sentence
The force of _______ acts between two solid surfaces in contact that are sliding across each other. The surfaces are ______ and will grip each other. This is why you need to exert a ______ to make something move. There are two drag forces __________ and _______. When a moving object is in contact with ______ or _______ particles it has to push them out of the way.
6. Why do breaks on a car need to be checked and replaced?
7. How do top athletes decrease their drag in the swimming pool.