Plans

Being a bit of a geek meant that I was rather excited about the new Tron movie. I was extra excited when I learned that it's release day (today) coincided with the day of my only exam this semester. I expressed a desire to go see it after my exam, at the Imax, by way of celebrating post-exam freedom.

Harry and Gav agreed to come along. We decided booking would be a good idea if we intended to go on the release day, and went directly to the Imax website. So, when it turned out that they had an early viewing of the film, starting at 00:01 on Friday 17th December - I could not resist.

"This is going to be perfect!"

Ten minutes after booking I realised that 00:01 was before 13:00, which is my exam time today. This meant that rather than getting an early night and plenty of rest, I was going to watch a sci-fi film at midnight.

I could have cancelled and booked later tickets. I admit that this was always an option. An option I ignored.

We got back at 3am. I'm sure my exam will go just fine, it is only general physics. Pass the coffee.

[Edit: 16:35: The film was awesome by the way. Oh, and yeah, the exam was fine.]

Frost

The sun is warm, but the ice is slippery.

I've always wanted to say that in context and today I could. Although most of the snow has melted, or been pushed into lumpy, icy piles at street corners, the pavements are now coated in a fine film of frost.

It's truly beautiful, of course. Sparkling and delicate and dangerous. It's amazing that this much water was there to freeze - I didn't think we had had much precipitation in the past week. The last we had was real snow.

It would be sensible to avoid leaving the flat until the frost melts. I do not have the necessary footwear, which I admit is a bit of a shock. You see, I no longer have a pair of walking boots, and I rather object to the idea of wearing walking boots in the middle of a city anyway.

Sadly it seems that my trainers do not have enough grip to deal with the frost. This is deduced from how often today I slipped on the ice. What if I had fallen? The risk isn't worth it. Perhaps I would have broken a bone. Perhaps my laptop. If I had fallen when crossing the street I could have been hit by a bus!

Worse! What if someone saw me? The indignity! I shall remain indoors.

General Physics Exam

Question:

If the law were changed so that traffic in Great Britain travelled on the right-hand side of the road instead of on the left, would the length of the day increase, decrease or be unaltered? Explain the reasoning behind your answer.

Answer:

It would be unaltered.

Driving in the opposite direction to the Earth's rotation may have some effect due to the conservation of angular momentum, but roads in Britain go in many directions, so the effect would cancel out.

When the driving in the opposite direction to the Earth's rotation, angular momentum is required, so when the car starts a small fraction is "robbed" from the planet. However, this will be returned as soon as the car stops - in fact, it is necessary if the car is to stop thanks to the conservation of angular momentum. Friction takes care of the stopping (and hence the return of momentum) for you.

Even if we assume that people drive in the opposite direction, and do not stop, sooner or later they are going to give in and come home. Probably they will do this before completing half a circuit of the Earth's circumference (after all, we're only looking at Britain), so it will make the most sense to come back the way they came. Travelling in the opposite direction will also return the momentum to the Earth.

If we ignore all this, and pretend that either stopping, returning, or other cars moving in other directions does not lead to a cancelling out of the removal of angular momentum, we still encounter a problem. The Earth is huge, your car is not. The effect of a car's momentum being gained from the Earth would be so minor that it would likely not be measurable, since the mass of the Earth is so much greater. So, since the difference between the mass of the car and the mass of the Earth is so great, the change in the length of the day would be negligible.

That is, unless your mum is driving the car. Fortunately, she's too stupid to drive.

I thank you.