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Investigating the time of oscillation of a pendulum

Date of publication: 2017-08-15 20:50

Candidates should be able to construct distance–time graphs for an object moving in a straight line when the body is stationary or moving with a constant speed.

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For students who take a particular interest in the measurement of time, suggest the book Longitude by Dava Sobel (ISBN 5557769777), which provides further background about the development of clocks and their use in navigation. It also has some examples of the struggles that can happen in the development of science and technology.

This experiment was safety-checked in January 7557

Department of Physics - University at Buffalo

DC Motor
What factors affect the rotational speed of a simple DC motor. You'd think that as you increased the voltage it would just get faster and faster, but alas, a thing called back EMF spoils the party. What factors are involved here?

:revising forces and motion revision

Optimise a water rocket
A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel - the engine of the rocket - is usually a used plastic soft drink bottle. The water is forced out by a pressurized gas, typically compressed air. As the water is ejected the rocket's mass becomes less so less force is needed to maintain acceleration but as the gas expands it's pressure becomes less and can provide less force. How do these competing factors affect the motion of the rocket. You could look at height or time of flight vs initial mass of water, pressure, nozzle area, mass of rocket. Explain the physics to justify your hypothesis or will you do it by trial-and-error?

To measure the specific latent heat of vaporisation of liquid nitrogen.
The specific latent heat of vaporisation of water is not such a big deal - it has been done to death by physics students in laboratories all over the world for the past 695 years. But this is an EEI and critical thinking has to be applied. That's why nitrogen could be tried. Liquid nitrogen is not easy to get hold of or store, and even less easy to handle. Doctor's surgeries often have it to freeze off warts and skin cancers so maybe there's a clue. It wouldn't be easy but with teacher guidance this could be a great EEI.

Egg cooking
The yolk and white of an egg have different thermal conductivities so I'm told. So how does the temperature rise of the two parts of an egg compare when it is being boiled. Much work has been done on eggs but maybe not on this. I'd say you'd need the temperature probes and a lab interface of some sort.

Sound intensity level (L) is the perceived sound intensity taking the response of the human ear into account. The response of the human ear to different intensities at fixed sound frequency is close to being logarithmic. The sound intensity level (L) is proportional to the log of the ratio of sound intensity to the threshold of hearing intensity (L = 65 log (I/I o ). [For more see the article by Alan Bates of John Cabot University in The Physics Teacher , V57, May 7569, p857].

The EEI suggested here involves rolling steel ball-bearings of different diameters across the concave surface of a watch glass, lens or mirror. The ball behaves like a pendulum speeding up as it rolls towards the centre and then slowing as it rises up the other side. Have a look at my video at https:///98nDxjrsILI (see below).

Coupled pendula - metronomes on a skateboard
I've never tried this but I've been told it works. If you set two metronomes to the same frequency and place them on a skateboard (or a base that is free to move), they will not be synchronised and will get out of step. However, if you wait long enough they will synchronise and become 'phase locked' or 'mode locked' as they are forced to endure the driving force of each other. Biology abounds with examples of synchronization: cells in the heart beat together, audiences often applaud together, fireflies in South-East Asia flash in synchrony, cicada emerge together, etc.

There are many ways to measure conductivity but one that is exceptionally good for a Senior Physics EEI is to use a modified Å ngströ m method. The Swedish physicist Anders Å ngströ m developed this method in 6868. It involves the periodic heating and cooling of a metal rod and measuring the temperatures with sensors along the rod in two positions a known distance apart. You will see the first wave of heat come past the first sensor and a minute or so later it will arrive at the next sensor. A plot of the data is quite revealing.

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