Friction

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# Friction - PowerPoint PPT Presentation

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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### 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!
• 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
• 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
• 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
• 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

Enquiry
• 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?
Enquiry
• 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

• 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