Pupils try to guess what tribology is – use images and the word itself to figure it out. If necessary: give a hint. It has something to o with a particular type of force. Tribology from Greek word “tribos” = to rub IMAGES: MS Office Cliparts http://server17.sitewizard.co.uk/sites/vehiclehandlingnew/images/big_rear_brake_kit1.jpg http://37prime.com/blog/wp-content/uploads/2008/03/ml_cat_tongue_02.jpg http://www1.imperial.ac.uk/resources/D89CC331-9282-47E4-B1F8-82F97BC96579/
Dictionary definition – complicated. For this lesson let’s simplify it. … So what happens when things rub together (e.g. your hands)? We observe friction. Heat energy is released (kinetic energy transformed into heat energy). If we rub our hands together for a week without stopping, what would happen to our skin (peel off, wear off)? Same happens to steel surfaces in a car engine. What would we use to prevent it (engine oil)? Other lubricants: grease, sometimes also water or air and other substances. IMAGES: http://www.studyzone.org/testprep/math4/b/monkey%20scratching%20head.gif
What does it mean that it is a contact force? If I want to push an object, which way will the force of push act? (demonstrate) Which direction would the friction force have? What will happen to the object when I push it? Is it going to slide forever (elicit that friction slows things down and stops them) ? Images: http://www.roymech.co.uk/images11/friction.gif
How did you know there was higher friction for wooden floor? – because the block didn’t go as far WHY?- depends on the surface material (rigid or soft) and texture (rough or smooth). Also, ice has a thin layer of water on top which acts as a lubricant (so similar to oil in a car engine). This is why we can do ice skating or skiing. It is not possible in very low temperatures when it is too cold for liquid water to be present on top of ice.
Needed: a small plastic bottle, loosely filled with dry raw rice grains + a chopstick (works well because it is long). The challenge is to lift up all of the rice in one go using just one chopstick and the force of friction. (lift up – not take anything out of the bottle). How can I do it? (take some ideas) Explanation: When the rice is packed closely together, e.g. by tapping gently the bottom of the bottle for a few minutes, and then the chopstick pushed inside all the way in, the rice grains are locked up so that the whole thing can be easily lifted. Show it to the pupils without explaining (have the bottle prepared beforehand or tap it while explaining the challenge and taking ideas) and ask if it can be done so easily each time (this time take another bottle and shake it up in an obvious way). The pupils should notice this time the rice is loose. If not, ask someone to squeeze the bottom part of both bottles – the first one should be hard (compact), the second – easy to squeeze (loose). How does this relate to friction? When rice is loose, there is not enough contact between the grains and there is more air between the grains which separates the grains; so it might be said it plays the role of a lubricant to some extent. Friction is a contact force, so there is less friction with less contact area. Pupils might also notice that loose rice seems to take up more volume. This is because of more air between the grains. Pupils should have a go themselves. IMAGES: http://www.andybrain.com/sciencelab/wp-content/uploads/2007/12/friction-and-rice.jpg
needed: 2 books with overlapping pages (can be every few pages, but no gaps between pages; some books work better than others- test beforehand). Challenge is to try separate them just by pulling, without ripping or opening them by hand. Have a few sets ready. First 2 students have a go in front of the class (make sure they obey the rules), then in groups of 5-6 pupils try to pull the books apart and figure out how to separate them (can try break the rules – what do you need to do for friction to not work anymore?). Possible explanation: no air between the pages means they’re tight in contact, so the force of friction acts against our pulling force. If we obey the rules (only pulling) – the books can be only separated with a very large force (see Mythbusters videos – they only managed to separate the books with 2 military tanks!). Would it work the same with other books? What if we would overlap every 100 pages only? (elicit: they would hold together better if there is more pages overlapping and for higher surface area of contact). Books can be separated if we try to introduce air between pages, e.g. by shaking the books (adding an additional force normal to the pulling force). Books may get damaged in this challenge. YOUTUBE LINKS: Mythbusters do phone books (start at 30s): http://www.youtube.com/watch?v=AX_lCOjLCTo Dutch Mythbusters (cars) (start at 3 MIN): http://www.youtube.com/watch?v=6sIB2kL-BWc Tanks (optional – long) (start at 5:16): http://www.youtube.com/watch?v=o8KYL53ZKU8 IMAGES youtube.com. http://www.adamsavage.com/images/pix/mythbusters.jpg http://www.darylscience.com/graphics/PhoneBook.jpg
IT GETS MESSY! Use plastic equipment and metal spatulas – not glass rods - for safety as pupils will apply force to test the properties of the slime. Needed per student group (2-3 pupils in the group maximum): a small plastic bowl a plastic measuring cylinder a plastic beaker with about 50 ml cornflour measured out a metal spatula for mixing some newspapers to spread on the tables for easier cleaning a few wiping cloths for cleaning up a spoon Some pupils might have done it before – ask what happens. When we mix cornflour with a small amount of water, it becomes a non-newtonian fluid (shear-thickening) – that means it behaves in a different way depending on how we apply the force on it. When we try to put our hand in the mixture slowly – it behaves like a liquid and flows. When we apply the force quickly (e.g. hit it) – it feels solid (explanation – next slide). Instructions: corn flour in the bowl. Add gradually the water (cold!) mixing until the right consistency (proportions above are just a guideline). I normally go around with some extra corn flour and add a bit more if necessary (pupils tend to make it too liquid). When ready – pupils can try doing different things with their slime (get your hands dirty!). IMAGES: http://www.csiro.au/files/images/p7tp.jpg http://www.scielo.br/img/revistas/cagro/v31n5/26f2.jpg
This behaviour is also similar to that of quicksand. IMAGES: http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/strange-cornflour-slime/
It is possible to walk on corn starch + water mixture. What advice would you give to a person trying to do that? What would happen if they stop? Youtube link (video in Spanish but it doesn’t matter what they are saying): http://www.youtube.com/watch?v=f2XQ97XHjVw Images: Youtube, http://www.skiptomylou.org/wp-content/uploads/2007/03/oobleck-1.jpg
In different applications friction can be useful (car breaks, tyres to provide grip on the road, use friction to light a match) or cause problems (resistance to motion, air resistance – type of friction – heats up the surface of a space shuttle on reentry). IMAGES: http://server17.sitewizard.co.uk/sites/vehiclehandlingnew/images/big_rear_brake_kit1.jpg http://www.slimfilms.com/graphics/8friction.jpeg http://www.biopoliticaltimes.org/img/original/push.gif http://ceipntrasradelapiedad.files.wordpress.com/2010/03/motion_friction2_240.jpg
space shuttle Columbia 2003 destroyed on reentry. thermal protection system failed – high heat in the upper atmosphere due to frictional heating up caused an explosion. Q&A: why does it heat up? what is air made of? elicit: air particles rub against the surface of the space shuttle. As it goes at a very high speed, this releases a lot of energy in form of heat. Can that happen in outer space / vacuum / outside the atmosphere? no, because there are no particles IMAGES: http://www.arcadiastreet.com/cgvistas/spacexp/images/se_spaceshuttle_reentry_800.jpg http://ceipntrasradelapiedad.files.wordpress.com/2010/03/motion_friction2_240.jpg http://news.bbc.co.uk/nol/shared/spl/hi/pop_ups/03/sci_nat_space_shuttle_columbia_disaster/img/2.jpg http://upload.wikimedia.org/wikipedia/commons/8/8f/STS-107_reentry.jpg
Low friction can be useful as well, but can be dangerous in some situations. IMAGES: http://www.ecoliblog.com/uploads/image/Water%20Slide.jpg http://3.bp.blogspot.com/-8VcSupxvjrA/TdMM2kN3llI/AAAAAAAAABQ/VRIAtlt48s8/s1600/PolarBearIce.jpeg http://upload.wikimedia.org/wikipedia/commons/c/ce/Australian_Slippery_Road_Surface_sign.png
maximizing and minimizing friction by equipment design and sport techniques IMAGES: MS Office Cliparts http://www.chelmsford.gov.uk/media/image/g/l/ice_skater_%28o%29_large.jpg
Source: http://kids.nationalgeographic.com/kids/stories/spacescience/basketball/ - autumn 2006 NBA wanted every basketball to feel and bounce the same. Synthetic balls introduced. -players complained: no grip, worse than leather -Dallas Mavericks owner asked for help from the Department of Physics at the University of Texas. -Findings: when balls dry: synthetic better (high friction, good grip). When wet (sweat): synthetic show no grip, leather absorbs sweat and even better grip than when dry. --In January 2007 the NBA went back to using the traditional leather balls Fast Facts: Leather balls absorb moisture eight times faster than the synthetic ones. Because it absorbs so much sweat, a leather ball may increase its weight by 10 percent during a game, but a synthetic ball remains the same. IMAGES: http://www.sportsbehemoth.com/wp-content/uploads/2011/04/NBA.png http://www.fanzof.com/wp-content/uploads/2011/05/1304427711-96.gif http://basketball-image.co.cc/images/mg/spalding_nbaball_hires.jpg http://kids.nationalgeographic.com/kids/stories/spacescience/basketball/
make-up should stay longer on the skin, be easy to spread evenly, feel smooth IMAGES: MS Office Cliparts http://images.mirror.co.uk/upl/m4/jan2009/8/6/282C13EA-A034-33AD-6B3289175EC79B57.jpg
Hair conditioners are designed to make hair... silky smooth they literally lubricate hair to detangle them and enable smoothness IMAGES: Film: “Don’t mess with the Zohan” http://farm4.static.flickr.com/3066/2635133226_123c2490e5.jpg http://ragrobyn.files.wordpress.com/2011/03/zohan.jpg http://g-ecx.images-amazon.com/images/G/01/dvd/sony/Zohan/Zohan_3lg.jpg http://www.bayareabags.com/wp-content/uploads/2010/04/homemade-hair-conditioner.jpg
IMAGES: own photo (red Ferrari) MS Office Cliparts http://www.khulsey.com/masters/inomoto_Formula_1_lg.jpeg http://www.indulgencecharters.com/images/london-eye-sunset.jpg http://i.ehow.co.uk/images/a05/rl/vk/replace-bicycle-wheel-bearings-800X800.jpg http://images.ifguk.co.uk/products/845/845-large1.jpg
traditional applications where mechanisms can be flooded with oil e.g. automotive engines, gears, bearings put a title slide before this IMAGES: http://m.twoknobbytires.com/media/bike_lubricant.jpg http://www.twincommas.com/wp-content/uploads/oil-gears.jpg http://dj-autos.co.uk/wp-content/uploads/2010/08/oil.jpg
thick, stay on the surface, doesn’t spill e.g. food industry, tree cutting: where we don’t want spillage IMAGES: Microsoft Office Cliparts http://image.made-in-china.com/4f0j00cCMTAPoDbazB/Grease-2.jpg http://www.get-into-cycling.com/images/crbb22.jpg http://www.sciencephoto.com/image/361504/530wm/T9300201-Loaves_of_bread_on_a_packaging_production_line-SPL.jpg
pressurized air creates a cushion: friction reduced e.g. hover boats other example: air bearing (restaurant) IMAGES: http://www.mutton.sk/Photos/800px/140.jpeg http://farm3.static.flickr.com/2366/2139897249_3f5022b386.jpg http://www.mech.kuleuven.be/apt/air_bearing.gif
powder or coating e.g. space, extreme pressure & temperature conditions IMAGES: http://www.outdoorfunstores.com/images/tube-coating.jpg http://www.nasa.gov/centers/goddard/images/content/121970main_astronaut_spacewalk.jpg
tailored chemicals e.g. medicine (safety, healing, research) IMAGES http://www.abc.net.au/health/library/img/hipjoint_diag.jpg Microsoft Office Cliparts http://maxshouse.com/eyedrops.jpg
Would Life Be
Dr A. Karpinska
Tribology is the science and engineering of interacting surfaces in
SO WHAT IS TRIBOLOGY?
Tribology tries to describe everything that happens
when things rub together
What is friction?
It’s a FORCE.
Occurs whenever two objects are IN CONTACT with each
It’s the resistance to movement. It SLOWS objects down.
Let’s use THE SAME FORCE to move the box on:
Which one will slide further?In which case friction is higher?
THE AMAZING FRICTION
Pick up thousands of rice
grains with a single chopstick.
THE AMAZING FRICTION
Pull apart two books with
MAKING CORNFLOUR SLIME
Cornflour Water Ratio
50 ml 25 ml 2:1
Cornflour is made up of lots of tiny (<0.01mm) angular starch
particles, these are very attracted to water so the water gets in
amongst them very quickly.
The water acts as a lubricant, so when you move it slowly the
particles have time to move past each other and they can flow like a
However if you apply a rapid force it causes the particles to move
slightly causing the particles that are almost touching to jam together.
and the water that was between them moves sideways slightly into
Now instead of having lots of lubricated individual particles you have
a solid structure of lumps touching each other which can't flow.
WHERE IS TRIBOLOGY?
corn flour +