Ten throws each

About this video

Nadia's fair test is ready in the school hall. She throws the pointed plane once: 6 metres. She throws the blunt plane once: 5 metres. "So pointed is better," says Leo. But Nadia isn't sure. Throw the same plane twice and it never flies exactly the same distance: the push, the angle, a tiny draught are a little different every time. So one plane can beat the other on one throw by luck. Is one metre a real difference?

To find out, Nadia throws each plane ten times, the same way, and marks where each one lands. The dots overlap: sometimes the blunt plane flew farther, sometimes the pointed one. On average, all ten distances added up and divided by ten, the pointed plane flew 5.6 metres and the blunt one 5.4. The difference in her first try was mostly luck.

Luck goes both ways. With one try, a lucky throw can decide everything; with many, the lucky and unlucky ones tend to even out, and what's left is the real difference, if there is one. A coin shows it: toss it 4 times and 3 heads is common, toss it 100 times and you'll almost always get close to 50. The things a test is done on are its sample, and how many there are is the sample size. The bigger it is, the less luck can fool you. This video goes with the Try It Many Times lesson of Science Level 1 on Knaph.

Transcript

1. 0:00One throw each. The pointed plane, six metres. The blunt one, five.
2. 0:05But no plane flies the same distance twice. Was one metre just luck?
3. 0:11Ten throws each, the same way. The dots overlap.
4. 0:17On average, five point six and five point four. The first try was mostly luck.
5. 0:23Toss a coin four times, three heads is common. A hundred times, close to fifty.
6. 0:29One try can be luck. Many tries even it out.