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Year 7 & 8 TOC


Drag & Friction

LO: Investigating the effects of applying different forces to familiar object
Drag & Friction

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, has to do with 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.

Have you ever had a static shock? When you drag your feet on the ground you build up a positive charge and when you go close to someone the charge jumps to the other object.

What is friction?

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. Friction is the force which acts in the opposite direction to motion. Different surfaces have different amounts of frictional force.

If there was no friction you:

  • would swim further and faster, with much less effort.
  • wouldn’t be able to walk anywhere because you’d constantly be slipping.
  • couldn’t drive because yours breaks wouldn’t work. 
  • couldn’t write with a pen because the pen would just slide of the page without leaving a mark. 

Types of 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.

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.

When moving through a gas (air) or liquid (water), there is some from of friction. This is called fluid friction.

Reducing friction

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.

Rollers or ball can be used to reduce friction. Like we said above, rolling an object across the ground requires less energy and force than sliding it. Ball bearings are often used to allow two surfaces to slide over each other with ease. 


Air resistance or drag, is the friction between the air and a moving object. When an object moves through the air, it bumps into particles from the air. 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

We can decrease drag by creating a smoother, rounder surface around an object. This makes the object streamlined. Cars, planes, trains, birds and fish all have streamlined bodies to make them move easier. 

Another method of decreasing drag is to use a slip stream. Riders and drivers will often ride very closely behind each other in a straight line. The person at the front has to deal with friction caused by the air so they expend more energy than the others. In fact, you can save up to 30% of your energy if you get into someone’s slip stream. 

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