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Veritasium
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These resources have been reviewed and selected by STEM Learning’s team of education specialists for factual accuracy and relevance to teaching STEM subjects in UK schools.
4 Revolutionary riddles
This video introduces 4 interesting physics problems about rotational motion. Students are asked to explain each problem.
1. A mystery object rolling down an inclined plank. The cylinder moves in a stop-start motion.
The container is filled with honey and 2 ping pong balls. The changing centre of gravity allows this strange motion.
2. If a runner could run a lap as slowly as they wanted, then run their second lap so that the average speed of the two laps was equal to twice the speed of the first lap. How fast would they need to run?
This is impossible because all of the time allowed has been used running the first lap! Even at the speed of light this could not be done.
3. Which part of a moving train moves backwards?
A diagram shows that it is the flange around the wheel, which is below the rail that moves backwards.
4. What direction will a bike move if a string attached to the pedal is pulled backwards.
The bike moves backwards. Watching the slow-motion video, it can be seen that when a bike is in forward motion, so too is the string with respect to the ground. It follows that pulling the string backwards will move the bike backwards.
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