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Friction - PowerPoint PPT Presentation

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Friction. D. Crowley, 2007. Friction. To understand what friction is, and how this affects movement. What is friction?. Rub your hands together quickly - what do you notice? This is first hand experience of friction!. Riding your bike.

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D. Crowley, 2007


  • To understand what friction is, and how this affects movement

What is friction
What is friction?

  • Rub your hands together quickly - what do you notice?

  • This is first hand experience of friction!

Riding your bike
Riding your bike

  • Before we define what friction is, think about riding your bike

  • What do you think affects how quickly your bike can stop? See if you and a partner can come of with three factors affecting a bike’s stopping potential

Stopping the bike
Stopping the bike

  • Type of surface you are cycling on - road / gravel / ice / mud?!

  • How quickly you are going - the faster you go, the longer it takes to stop

  • Type of brakes you have - the better the brakes (e.g. disc brakes) the quicker they can stop you

  • How good are your tyres? Do they grip the road well, or are they more like slicks?

  • How much are you carrying - the more you have on your bike the more energy you will have at a given speed - so the more energy it will take to stop you!


  • Friction is a force which occurs when two objects interact

  • If an object has no force propelling it, it will slow down and eventually stop due to friction

  • Rubbing your hands together causes friction - causing your hands to heat up

  • Friction can occur in many ways, including the following…


  • Friction occurs between solid surfaces which are gripping / sliding past each other (e.g. a tyre on the road / marble down a ramp)

  • Resistance (drag) from the air or liquid - as you move air or liquid particles collide into you (this is why a parachute slows you down and to go very fast cars need to become streamlined)

  • Friction increases as speed increases - more speed = more air particles colliding into you

Friction between two surfaces

Friction increases as speed does

Air resistance - example of friction


  • Your task is to investigate how quickly you can get a block of wood to slide down a drain pipe

  • You have a variety of materials to help you achieve this, including: foil; dusters; polish; doweling etc...

  • You must think about what results you want to collect, and what bits of information you must record

  • What must you keep the same during the experiment and why? How can you measure the objects speed - what information do you need to collect to calculate this?


  • You need to write down on the sheet a short draft of the experiment your are going to do + a hypothesis of what you think will happen

  • What variables are you changing / keeping the same?

  • How are you going to measure the results (what will be in your table, and will you repeat)?

  • Conclusion - what do you find out?

Some surfaces limited the speed the block moved at, due to much greater frictional forces

All bad
All bad?

  • Friction, such as air resistance slows objects down

  • But it is not always bad - you and your partner now need to write down some examples of friction when it is being bad (for us), and when it is being good

Friction bad
Friction - bad

  • Air resistance slows vehicles down, so the engine needs to propel them (it must work harder at higher speeds)

  • Friction makes it difficult to swim through water quickly

  • Friction causes wear and heating - machines which have parts which touch / slide over each other produce lots of heat and wear - meaning they need lubricants

Friction good
Friction - good

  • Air resistance slows vehicles down, which can be very useful for vehicles such as the space shuttle which use the Earth’s atmosphere to slow it down, allowing it to land

  • Parachutes utilise air resistance to slow people down, when falling to Earth

  • If there wasn’t any friction we couldn’t slow our bikes down - brakes utilise friction to our advantage

  • We wouldn’t be able to move without friction - just as low friction surfaces such as ice as hard to walk on, no friction would be impossible!

  • Friction holds nuts and bolts together etc…


  • Why is it harder to run through water, than it is to run through the air?

  • Answer this question using your new knowledge of friction

  • If you finish this, can you think of ways we could get through the water more quickly (using scientific ideas)