science friction...
A deserted street, West Berlin, 1971, freezing snowy mid winter. Chief of Intelligence, Herr Resistance, shivers in the freezing wind. He rubs his hands together briskly to keep them warm and curses as he slides on the ice. He mutters abrasively...
RESISTANCE: “These pesky shoes – they’ve no grip!”. His mobile phone rings.
RESISTANCE: Friction? Is that you? Stop dragging your feet. I need you here – get your skates on!
In the distance there's the sound of tyres screeching. A car skids to a halt. Out jumps Special Agent Frankie “The Burn” Friction. Resistance barks icily to him.
RESISTANCE: ‘Lo Friction
FRICTION: (Roughly) Hi! I gather this involves Motion?
RESISTANCE: Doesn’t it always? Perpetua Motion is on the move.
FRICTION: That dame's a dream. If only….
RESISTANCE: Forget it, many have fallen under her spell, but you know she's unobtainable Friction, plus she's our arch enemy. Let’s get up to speed: Yesterday, international smuggler Sly Ding greased up his handcuffs and slithered free. He strapped on a pair of skis and slid off. He was last seen hurtling down the bobsleigh run. Who knows where it will end? We need you Friction. You’re the only man for the job.”
FRICTION: “Stop Sly Ding? Me? You’re asking a lot! Motion is out of control this time and I hear Lou Briquant is involved too?”
Friction shivers at the thought.
RESISTANCE: Lou Briquant? The oil magnate? He knows you Friction, a force to be reckoned with.
FRICTION: He's a smooth operator though…
RESISTANCE: (Shouting) Get a grip Friction! We need to put the brakes on. Motion knows that without Friction there’ll be no stopping Sly Ding”
to be continued... by YOU!
science friction
What is it? Well friction is a force between two surfaces. It tries to slow moving objects down and makes it difficult to move stationary objects. In other words it opposes motion. Try pushing a toy car across the carpet; now try pushing it across a tiled or wooden floor. Feel the difference? The rougher the surface the more friction is produced which slows moving things down.
Friction also makes things hotter. Rub your hands together very quickly. How does it feel?
When two surfaces are rubbed together they produce friction. Sometimes this is a good thing and sometimes it is bad.
friction is good:
We need friction. Imagine life without it - everything would slip and slide about. We need friction between our feet and the ground else we would not be able to stand up. We need friction between our car tyres and the road else we would skid and crash. And imagine if there was no friction between our brake pads and the wheels - oops! Watch out!
Take a look at what happens if you don’t allow yourself enough braking distance on icy or snowy roads.
friction is bad:
Friction can make things hot. Remember how cavemen made fire by rubbing two sticks together? Causing heat to build up is not always a good thing, especially inside a car engine.
Oil is used to lubricate the parts of a car engine so that it runs smoothly. The oil makes the surface smoother so there is less friction, less wear on the metal and hence less risk of fire.
more friction:
Air resistance is a sort of friction. Air particles hit your body as you run and try to slow you down. Try running holding a sheet of card in front of you – can you feel the air resistance pushing against the card? Pointed objects move faster through the air than other shapes. This is known as streamlining.
Look at the shape of aeroplanes, arrows, rockets and cars. They are all shaped so as to move through the air as quickly as possible. This is known as aerodynamics. In sports athletes often wear clothing that is tight fitting and smooth. This helps to cut down on air resistance. They arrange their bodies so that they run in the most aerodynamic way - look at the position they adopt in the starting blocks.
To get a better idea of how aeroplanes move through the air try making your own paper aeroplanes.
let’s have a look at friction in action:
Ice causes very little friction which is why it is so easy to slip over in bad weather. However, it is good news for those who want to ski or to ice skate. Ever wondered about the Science Behind …. Winter Sports?
Also friction is very important for those who love to skateboard. How do you think they perform those tricks where their feet seem to stick to the board? And how do they manage to stop so suddenly and turn the board at crazy angles at the top of ramps? Yup! It’s down to friction again.
Whe-he-he-hay! Just slipped on a banana skin? Very funny (not!). Definitely a case of very low friction. If you don’t want to slip over then you need to be sure that the soles of your shoes have very good grip.
Have you noticed the patterns on the soles of your trainers? They are not just there to look good you know! A scientist has very carefully worked out the exact positions on the sole of your foot that requires the most grip. Look particularly at the bits near your toes and heels. Hmmmmmmmmm! Very interesting. If you want to help design some trainers then have a look at Mr Zippy’s Trainers.
things to do
make a hovercraft activity
Take an old CD and glue a cotton reel to the centre so that the hole in the reel is directly over the hole in the CD.
Blow up a balloon, twist the neck and hold it so that the air does not escape.
Stretch the neck over the cotton reel.
Put your hovercraft on a flat smooth surface.
Now loose the balloon and give the CD a flick. It should move along the surface on a cushion of air.
what is happening?
The air in the balloon has to go somewhere. So, it flows out of the balloon and goes under the CD. The layer of air under the CD takes up space so it keeps the CD and table from rubbing on each other. When objects rub against each other, they create friction. Friction drags on each object and slows it down. The Hovercraft has very little friction because it rests on air.
stack of coins activity
Make a stack of ten 2p pieces on a smooth surface.
Do you think you can remove the bottom coin without knocking the stack over?
you will need:
Ten 2p coins
A butter knife
A smooth surface
what to do:
Make sure your stack is really straight.
Now take a butter knife and place the edge of the knife against the bottom coin.
Give it a quick tap and the coin should shoot out the side of the stack and leave the rest standing.
How tall a stack can you make? Will it still work? What happens if you tap the coin slowly?
what is happening?
Take a look at the stack of coins - they are at rest, or not moving. Objects at rest don't move unless you push or pull them. So, to make the bottom coin move, you need to push or pull it. To make it move without knocking over the whole stack, you need to push or pull quickly. Why? Because of friction.
Friction is a "sticky" force that appears when two objects (like coins) rub against each other. If you push the bottom coin slowly, friction helps pull the stack along with it by "sticking" the coins together. If you push the bottom coin quickly, the coins still rub, but the friction force doesn't have time to get the stack moving. So, the coin shoots out without pulling the stack with it.
ball bearings activity
you need:
A small food can
Marbles or cake decoration balls (try the Baking section of the supermarket)
Pencil
Lid that fits over the base of the food can
Plasticine or Blutak
what to do:
Turn the can over so that the base is topmost (that’s because most cans now have a ring pull which could complicate things).
Make sure that your lid loosely fits over the can so that it can spin.
Form two balls of plasticine and put them on the ends of the pencil.
Fix the pencil to the lid with plasticine.
Now try to spin the pencil. What happens?
Take the lid off and add the marbles or cake decoration balls.
Replace the lid and give the pencil a spin. What happens now?
what is happening?
Friction is reduced if we replace sliding with rolling. When the lid spins on the can surface it slides and there is friction between the lid and the can. This slows it down so that it spins for only a short time.
If we use spheres between the two surfaces then a rolling movement replaces the sliding movement. The friction is greatly reduced and the lid spins faster and for a longer time. That is why we use ball bearings in many machines. Ball bearings are also used in many wheel applications such as roller skates, skateboards and bicycles.
balloon rocket activity
you need:
A drinking straw
A long balloon
About 2m of string
A clothes peg or bulldog clip
Washing up liquid
Sticky tape
Two chairs about 2 m apart
what to do:
Blow up the balloon, fold up the neck and put a peg or clip on it to stop the air coming out. (Warning: please do not inflate the balloon if you are under 8 years – ask an adult to do it)
Thread the string through the drinking straw.
Tie each end of the string to two chairs placed a distance apart. Make sure the string is at least 30 cm off the ground
Pull the straw to one end of the tied string and stick the straw lengthways to the balloon using sticky tape
Remove the peg or clip and watch your rocket zoom away!
Measure how far it goes and then repeat the activity but this time RUB A LITTLE WASHING UP LIQUID ON THE STRING FIRST.
what is happening?
When the air from the balloon rushes out backwards it propels the rocket forwards. If the friction between the string and the straw is high then the rocket will only go a short distance. However if the friction is low then the rocket will go much further. The washing up liquid will act as a lubricant on the string. This lowers the friction and makes the rocket go further.
How about designing a paper rocket to stick to your balloon. Remember to design a shape that will move through the air quickly. For the fastest rocket you will need an aerodynamic shape and very low friction between the straw and the string.
remember:
* Friction is a force between two surfaces;
* Friction is low if the surfaces are smooth and wet;
* Friction is high if the surfaces are dry and rough;
* Friction causes heat;
* Friction can be reduced by using lubricants, ball bearings, air-cushions and by streamlining
If you want to check what you know about friction take a look at BBC ReviseWiselesson ideas for teachers:
Friction – effect of weightFriction – effect of surface
Friction – effect of rolling
Friction – effect of lubricants
Lesson ideas – Friction in our lives
friction prediction
In the ol’ Wild West, the doors slam open in the Slippy Surface Saloon. There stands Sly Dingforce, the nasty varmint. “Set ‘em ‘up bartender!” snarls Sly, his hand slamming down on the bar.
Nervously the bartender pours a slug of liquor and slides it down towards him. It stops about a yard away from his outstretched hand.
The tinkling piano music stops.
All is silent.
The bartender croaks, “ Write on my headstone... too much friction!”
