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Skip to 0 minutes and 7 seconds TEACHER: So which size sail is this one?

Skip to 0 minutes and 9 seconds STUDENT: 50 centimetres.

Skip to 0 minutes and 10 seconds STUDENT: 50 centimetres.

Skip to 0 minutes and 11 seconds TEACHER: 50 centimetres [squared]. So we need to be recording it down, and did we reset there boys?

Skip to 0 minutes and 15 seconds STUDENT: Yeah.

Skip to 0 minutes and 16 seconds STUDENT: I think 3, 2, 1, go.

Skip to 0 minutes and 18 seconds STUDENT: Start.

Skip to 0 minutes and 23 seconds STUDENT: I think she got closer to it. [INTERPOSING VOICES]

Skip to 0 minutes and 27 seconds STUDENT: Five second for 18.

Skip to 0 minutes and 28 seconds TEACHER: OK, stop there a second. Was there anything else that was being a problem there then?

Skip to 0 minutes and 32 seconds STUDENT: [GASPS] Yeah.

Skip to 0 minutes and 33 seconds TEACHER: Yeah?

Skip to 0 minutes and 34 seconds STUDENT: [INAUDIBLE]

Skip to 0 minutes and 34 seconds TEACHER: OK, Essen, maybe you need to try and do that. Anything else that was a problem with the actual boat?

Skip to 0 minutes and 39 seconds STUDENT: It cut back and into the side.

Skip to 0 minutes and 41 seconds TEACHER: Cut back into the side. Start thinking about last week, what’s that going to have an effect? You’ve got a boats in the sides.

Skip to 0 minutes and 46 seconds STUDENT: On the friction.

Skip to 0 minutes and 48 seconds TEACHER: We’re going to have some friction playing a part, and all of a sudden our question of wind resistance. Uh-uh. Blows them apart. So we need to maybe adjust the sail. Think about how straight the fan is because the first run was spot on. It just moved, and it went straight down the side. If it happens, it happens. We want to try and minimise all of this as possible.

Skip to 1 minute and 5 seconds STUDENT: Ready?

Skip to 1 minute and 8 seconds STUDENT: 3, 2, 1, go.

Skip to 1 minute and 10 seconds TEACHER: Much better. Got a little bend though.

Skip to 1 minute and 14 seconds STUDENT: [INAUDIBLE] [INTERPOSING VOICES]

Skip to 1 minute and 18 seconds STUDENT: And the fan moves closer to the boat.

Skip to 1 minute and 20 seconds STUDENT: [INAUDIBLE]

Skip to 1 minute and 22 seconds TEACHER: Three. Three.

Skip to 1 minute and 25 seconds STUDENT: .46 seconds.

Skip to 1 minute and 26 seconds TEACHER: OK. 3.46 seconds. Let’s take that one. We can give them all a second test maybe. And then they go down the line. What do we need to do now?

Skip to 1 minute and 34 seconds STUDENT: Change sails.

Skip to 1 minute and 35 seconds TEACHER: Change the sails.

Skip to 1 minute and 37 seconds TEACHER: What did we find out then, guys? Go on, Josh.

Skip to 1 minute and 39 seconds STUDENT: Smaller sails go faster.

Skip to 1 minute and 40 seconds TEACHER: The smaller sails go faster, but what was our prediction? Pippa.

Skip to 1 minute and 45 seconds STUDENT: That the biggest sail would go quicker.

Skip to 1 minute and 47 seconds TEACHER: Good. The bigger sail. Why did we think that the bigger sail would go quicker? What was the educated guess behind that? We didn’t take a silly guess. We thought about it.

Skip to 1 minute and 55 seconds STUDENT: Because it’s bigger, the wind will be able to hit more stuff, but hit the bigger surface, so it would go faster.

Skip to 2 minutes and 1 second TEACHER: Yeah, brilliant. We’ve got more of the air particles hitting the surface, a bit like friction if we think about friction. A smaller area would generate less friction, so surely the smaller area of the sail would get less wind resistance. But we got the opposite. Why? Give us some reasons because it’s not necessarily wrong. Our predictions weren’t wrong, but we’ve got a lot of other things that have been taking place. Why do you think this is what happened? Max.

Skip to 2 minutes and 23 seconds STUDENT: Because the big ones, they’d be more heavy than the small ones, they’d be lighter than the big ones.

Skip to 2 minutes and 31 seconds TEACHER: OK, so what are those are those heavy sails? You say it’s bigger, they’re very slightly heavier. And what problem does that cause? Need you to settle a second for me, Josh. Go on, Max.

Skip to 2 minutes and 40 seconds STUDENT: The fan, it’ll be more heavy for it to move across the water.

Skip to 2 minutes and 45 seconds TEACHER: OK yeah, so maybe a bit more, we’d call it maybe drag, because the weight would add a bit more drag to it. What else?

Skip to 2 minutes and 51 seconds STUDENT: Because the fan wasn’t straight, and it was heading towards the sail. It was heading to the left.

Skip to 2 minutes and 59 seconds TEACHER: OK yes, so we also have another variable. Not just size and the weight, but the direction of the fan caused it to go off. And that caused other problems. It kept crashing, and yeah. Layla.

Skip to 3 minutes and 7 seconds STUDENT: The smaller ones would also be easier to control with the fan.

Skip to 3 minutes and 11 seconds TEACHER: OK yes, the larger it was, the less control we had over it. The smaller ones we had a bit more control, so we didn’t have as much crashing. But it did crash into the side. Scientifically speaking, what force did we have acting also on the boat then?

Skip to 3 minutes and 23 seconds STUDENT: Friction.

Skip to 3 minutes and 23 seconds TEACHER: Friction. And Max, you mentioned about it being heavier. What was going to happen to the boat if it was heavier?

Skip to 3 minutes and 28 seconds STUDENT: It would sink.

Skip to 3 minutes and 30 seconds TEACHER: It would sink, and then what other force have we got acting a lot more of?

Skip to 3 minutes and 33 seconds STUDENT: Water friction.

Skip to 3 minutes and 34 seconds TEACHER: Water friction. It is a type of friction, but we call it water–

Skip to 3 minutes and 39 seconds STUDENT: Resistance.

Skip to 3 minutes and 40 seconds TEACHER: Good, water resistance.

What has slowed the boat down?

In this video children are investigating the effect of changing the size of a sail on a boat.

They use fans to generate wind power to push the boats forward, and predict that the largest sail will move the fastest. In their investigation they found that the smallest sail was the quickest.

Observe

Watch the video and see what ideas the children have for why the largest sail is not found to be the quickest. How could you explain this to them?

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This video is from the free online course:

Teaching Primary Science: Physics

National STEM Learning Centre