Friction D. Crowley, 2007

Friction  To understand what friction is, and how this affects movement Tuesday, August 04, 2015

What is friction?  Rub your hands together quickly - what do you notice?  This is first hand experience of friction!  Rub your hands together quickly - what do you notice?  This is first hand experience of friction!

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  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!  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 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 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 surfacesFriction increases as speed doesAir 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?  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?  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?  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, 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  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  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  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…  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…

Question  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)  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)