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First Year Physics

Van de Graaff Generator

I love playing with the Van deGraaf Generator. It feels a bit like magic. The only bit of the explanation missing from the video is why the tissue paper that jumps back and forth between the large aluminum dome and the smaller earthing dome, is initially attracted to the charged dome. The tissue paper should not have had any initial charge so there should not have been an initial force to make it move.

Charging By Induction

Trying to demonstrate charging by induction using a small conical flask at the front of the lecture theatre has never worked very well, even when using the camera on the video overhead projector so this video was created. If there was time it might be interesting to get students to create their own electroscopes. And embed them in an interactive artistic piece of work.

Resonance In A Rotating Tube

I must admit I am not sure how this works. In the video I propose that it is the speed of the air moving through the tube that changes the frequency but now I am not so sure. So let’s try and work it out step by step (logically).

What we know: The faster you spin the tube the higher the frequency it resonates at.

What we infer: The faster the tube spins the faster the air is flowing across the mouth of the spinning end of the tube. The end with the fast moving air will produce a zone of lower pressure compared to the more stationary end.

Resonance & Standing Waves

Standing waves on a string form from the sum of two waves, one moving down the string and the reflected wave coming back. Normally these two waves would pass along the string and the standing wave pattern would not be seen. The amplitude of the two waves would add up to give a total which would change over time as the two waves move in opposite directions. However the frequency of the speaker is the critical factor here. If it is providing pulses at just the right frequency standing waves will form.

Buoyancy Fish – Make at home

The students could have fun making these themselves. Hands-on is good. The activity is something different and if the finished product works then the students will get ample opportunity to explain how it works to family and friends. This will give them many opportunities to engage with the language and get the concepts straight in their head as well.

Buoyancy – Galileo’s Thermometer

I am happy with the explanation in this video. I think students would need to draw free-body force diagrams to understand the physics behind the thermometer. In one of my assignments I asked my students to look up how the density of water changes with temperature. Then work out how much sand they would need to put into ping pong balls to get them to sink at a set of given temperatures, effectively creating their own Galilean thermometer.

Collisions

I can’t think of anything extra to add to this video it is fairly self-explanatory. It might be interesting to work out how much energy is lost with the collision between the lead balls. 1mv in and 1mv out as momentum is conserved but 1/2mv2 in and ½(5m)((1/5)v)2 out which is 1/5 of the original energy out. Where did it go? If there were two lead balls the energy out would be half of the energy in. Three balls it would be one third, four balls, one quarter. An infinite number of balls and the energy out is so close to zero that it does not matter.

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