Vortex Shedding in Air Friday, April 8, 2016

A thin wire, moving through the air, is made to vibrate in the audio range at the vortex shedding frequency.

What it shows:  When air flows around an object, there is a range of flow velocities for which a von Karman vortex street is formed. The shedding of these vortices imparts a periodic force on the object. The force is quite small and not enough to accelerate the object to any significant amount, especially if the object is relatively massive. If the situation is such that the object can vibrate about a fixed position, we have the possibility of simple harmonic… Read more about Vortex Shedding in Air

Jumping Wire

What it shows:

A current carrying wire in a magnetic field experiences a force at right angles to both the field and current directions. The wire will jump up or down, depending upon the current direction.

How it works:

On a microscopic scale, the electrons in the wire experience a Lorentz force due to the magnetic field,

the force perpendicular to both field and velocity vector. On… Read more about Jumping Wire

Brewster's Angle

What it shows:

When unpolarized light is reflected from a non-metallic surface, the reflected ray is plane polarized parallel to the reflecting surface if

θi + θr = 90°


tanθi = n

where θi = incident ray (Brewster's angle), θr = refracted ray, n = refractive index

How it works:

We use a black vinyl sheet 1m×4m as the reflecting surface, which has a Brewster angle of 57°. A theatrical spot lamp 1 is used to… Read more about Brewster's Angle

Galileo's Chandelier

galileo's chandelierBowling ball pendulum with burning candles stuck in holes, used as prop only.

What It Shows

Rumor has it that one day at the cathedral, Galileo watched the swinging of a chandelier after it had been displaced and lit. By using his own pulse as a timer,… Read more about Galileo's Chandelier

Inverted Pascal Experiment

What it shows:

This is a concept question relating to Pascal's cask-bursting experiment. Imagine the experiment inverted—literally! Attach a 20-ft length of tubing to the opening of a can full of water. Turn the can upside down and raise it high. Will the water stay in the can, or will it run out? Will atmospheric pressure hold up the column of water in the tubing? What will happen? Have the class vote.

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Continuous Spectrum

What it shows:

White light is shown, á la Newton's demonstration of dispersion by a prism, to be composed of a continuous spectrum of colors.

How it works:

A large brilliant spectrum is produced by using a 1 kW carbon arc light source 1 with adjustable slit, a "fast" f/0.9 imaging lens, 2 and a highly dispersive in-line prism. 3 The spectrum easily fills a two meter wide screen with vibrant colors. An alternative (more compact) setup consists of a Beseler slide projector 4 which… Read more about Continuous Spectrum

Neutron Activation of Silver

What it shows:

One of the more important discoveries in modern physics is the production of isotopes (both radioactive and stable) by the capture of neutrons. 1 In this experiment the bombardment of silver by thermalized neutrons produces short lived radioactive isotopes of silver whose half lives can readily be measured. It can also be shown that bombardment by fast neutrons does not induce radioactivity because of the extremely low neutron cross sections involved. Using a Geiger counter in conjunction with a multichannel analyzer in the MCS (… Read more about Neutron Activation of Silver

Newton's Apple

Apple electronically released from platform; fall time given by special circuit and digital display.

What it shows:

This is a free-fall-from-rest experiment in which an apple (or any other object of comparable size) is dropped from the lecture hall ceiling into a catching bucket on the floor. By measuring the (1) distance and (2) duration of the fall, an accurate (± 0.022%) determination of the acceleration due to gravity can be made:

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