Steve tells us his hypothesis to explain the cokes: He thinks that heavy things always sink and light things always float.

Transkript

1 Physics - Archimedes Drank Diet Coke - Overview In this clip the professor introduces Archimedes law to Steve and the students. The clip starts with the professor relaxing by the pool and Steve bringing a can of regular coke and a can of diet coke. Steve then trips and the cans of coke fall in the water and we watch as the diet coke then floats, but the regular coke sinks to the bottom of the pool. This then sets Steve and the Prof off to investigate buoyancy and water displacement. Steve tells us his hypothesis to explain the cokes: He thinks that heavy things always sink and light things always float. While walking around the pool, the Prof sets the students the task of collecting some everyday objects together and to predict and test whether they sink or float. The students write their predictions and results on the handout. The first column should be filled out using the future form will because at this stage the students are thinking at the time but when the experiment is to be repeated the students fill in the next column using the going to future form because they are talking about the future with a degree of confidence and are not now making their minds up at the time of writing. This is the key language point of the clip. At the end of this scene we finally see that Steve floats, even though he is very heavy before we go to the lab to explain Archimedes law. In the laboratory, the professor tests Steve s hypothesis by putting two equally weighted objects in a tank of water, but because of the amount of water displaced by making them into two different shapes one floats and one sinks. Steve and the students are asked to predict whether each one will sink or float before each test. Towards the end of the clip we return to the original problem, the Prof explains why the regular coke sinks, and asks the students to explain why the diet coke floats. Steve (and the students are now set a challenge to get the coke out of the tank without touching it, and after several failed attempts by Steve, the Prof shows the students how the density (and thus boyency force) of water can be changed by adding salt.

2 Suggested Pauses: 01:11 Why does the regular coke sink and the diet coke float? Do you agree with Steve? Elicit ideas and continue watching to find out. 01:46 - Give the students the handout and help them carry out the task Please collect some classroom objects together. Which objects have you collected? Make your guessed by writing I think it will sink / float in the first column Test your predictions and record the results with a tick or a cross. 02:12 Encourage the students to fill in the rest or the handout. Say You now know what s going to happen when you put your objects in water, so please write it s going to sink / float in the second column. 02:51 What is the Prof holding? A coin and a piece of aluminium foil. Do they weigh the same? Yes 03:12 Encourage the students to answer the question will it sink or float with a show of hands. 03:45 Encourage the students to answer the question will it sink or float with a show of hands. 04:29 Why did the ball sink? Because the buoyancy force was too low / it doesn t push enough water out the way. 04:45 So does the boat push more water out of the way then the ball? Yes Why It has a greater surface area. So why does the boat float

3 Because the buoyancy force was high enough / it pushes enough water out the way to counter its weight. 05:35 How many spoonfuls of sugar are in the regular coke? 9.75 So is it lighter or heavier then the diet coke? It s heavier So why does the diet coke float? Its lighter 05:59 How do you think the professor can get the regular coke out of the water without touching it with anything? Elicit ideas from the students then watch until to find out that the Prof uses salt to change the density of the water. 07:04 Is salt water easier or harder to move out of the way than fresh water? It s harder because it has a higher density. What does the change in density do to the buoyancy force? It increased the buoyancy force. So what would happen if you took a battle ship out of the salty sea and put it into a freshwater lake? It would probably sink. 07:19 Do you think Steve and the Professor will sink or float?

4 Fyzika - Archimedes Drank Diet Coke V tomto klipu profesor prezentuje Stevovi a žákům Archimédův zákon. Popis situace: Profesor odpočívá n zahradě u bazénu. Steve přináší plechovku standardní Coca Coly a plechovku dietní Coly. Steve náhle zakopne a obě plechovky upustí do bazénu. Plechovka s dietní Colou plave, ale plechovka se standardní Colou klesá ke dnu bazénu. To Steva a profesora přiměje vypátrat vztlak a výtlak vody. Steve vysloví domněnku: myslí si, že těžké věci vždy klesají ke dnu a lehké věci vždy plavou na hladině. Profesor zadá žákům úkol, aby posbírali několik předmětů denní potřeby a tipovali a následně testovali, zda se potopí nebo poplavou. Žáci zaznamenají své tipy a výsledky testu na záznamový arch. První sloupec bude vyplněn s WILL (v této fázi žáci přemýšlejí, domnívají se), ale když se má pokus opakovat, žáci vyplní druhý sloupec archu s GOING TO (mluví o budoucnosti už s určitým stupněm jistoty). Toto je tedy klíčový jazykový bod daného klipu. Na konci této scény vidíme, jak Steve plave, přestože je velmi těžký. Další scéna se odehrává v laboratoři, kde profesor ověřuje Stevovu domněnku. Dva stejně těžké předměty vkládá do nádrže s vodou. Před samotným testem Steve a žáci jsou vyzváni, aby tipovali, zda budou předměty plavat nebo se potopí. Postupně se dostáváme zpět k původnímu problému. Profesor vysvětluje, proč se standardní Coca Cola potápí, a ptá se žáků, proč plechovka s dietní Colou plave. Steve a žáci mají přemýšlet, jak dostat Colu z nádrže ven, aniž by se jí dotkli. Po několika Stevových neúspěšných pokusech profesor ukazuje žákům, jak lze hustotu (a tím vztlakovou sílu) vody změnit přidáním soli. Doporučené pauzy a otázky/úkoly pro studenty během sledování klipu: 01:11 Why does the regular coke sink and the diet coke float? Do you agree with Steve? Necháme studenty tipovat a pak pokračujeme ve sledování klipu, dokud neuslyšíme odpověď.

5 01:46 Každému žákovi rozdáme záznamový arch a pomáháme jim při plnění úkolu. Společně nashromáždíme několik předmětů denní potřeby. Předměty společně pojmenujeme. Žáci své domněnky zapisují do prvního sloupce v archu: Make your guessed by writing I think it will sink / float in the first column. Následně svá tvrzení ověří pokusem a výsledky zapíší: Test your predictions and record the results with a tick or a cross. 02:12 Žáci vyplní zbývající část listu, tj. druhý sloupce, kde již používají vazbu going to. Řekneme: You now know what s going to happen when you put your objects in water, so please write it s going to sink / float in the second column. 02:51 What is the professor holding? - A coin and a piece of aluminium foil. Do they weigh the same? - Yes 03:12 Žáci odpoví na otázku Will it sink or float? zvednutím rukou. 03:45 Žáci odpoví na otázku Will it sink or float? zvednutím rukou. 04:29 Why did the ball sink? Because the buoyancy force was too low / it doesn t push enough water out the way. 04:45 So does the boat push more water out of the way then the ball? Yes Why? It has a greater surface area. So, why does the boat float?

6 Because the buoyancy force was high enough / it pushes enough water out the way to counter its weight. 05:35 How many spoonfuls of sugar are in the regular coke? 9.75 So is it lighter or heavier then the diet coke? It s heavier. So, why does the diet coke float? It s lighter. 05:59 How do you think the professor can get the regular coke out of the water without touching it with anything? Žáci sdílejí své nápady, potom sledujeme klip až do 06.45, kdy zjišťujeme, že profesor sype do vody sůl, aby změnil hustotu vody. 07:04 Is salt water easier or harder to move out of the way than fresh water? It s harder because it has a higher density. What does the change in density do to the buoyancy force? It increased the buoyancy force. So what would happen if you took a battle ship out of the salty sea and put it into a freshwater lake? It would probably sink. 07:19 Do you think Steve and the Professor will sink or float?