Here is an animated gif of the Pumpless fountain demonstration. The full video can be found here. Pumpless Fountain An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations. How to build a fountain without a pump. Tweet ..read more

A pumpless fountain. This is a demonstration that was shown to me by Jim Pohl a while ago but I have only just found the time to have one built. The original post by Jim Pohl is here. It is conceptually very elegant. Two sealed containers are partially filled and have fully flooded tubes that lead to an upper reservoir. The two sealed containers are connected by an air-filled tube such that the surface pressures in the containers are always the same (or almost identical as the hydrostatic pressure variation in the air is orders of magnitude smaller than in the water.) If one of the sealed cont ..read more

Can you tell the direction of flow of a box fan just by looking at the frame? Tweet This is another question I posted in a discussion board for my online junior level fluid mechanics class. Below are two photographs of a box fan showing views from the right and from the left. The question is, knowing what you do about angular momentum, which direction does the air flow when the fan is turned on (right to left or left to right)? View from the left                          ..read more

Introduction My 7 year old daughter has been learning about states of matter in school and had to do an experiment to see if gasses have mass. The experiment involved balancing 2 inflated balloons on either end of a stick and then popping one of them. The idea being that, because all the air escapes from the popped balloon, the un-popped balloon will be heavier (because of the weight of air inside the balloon. The video of her experiment is linked here. I posted this in my junior level fluid mechanics class discussion board and asked my students if this was a valid experiment to show that gas ..read more

Many science museums have demonstrations in which a ball is levitated by an air jet. Typically the ball is quite light and the air jet quite broad. These setups can produce reasonably stable results with the ball staying supported by the air jet. They even work when the air jet is inclined. There are occasionally explanations associated with the demonstration talking about how the drag from the air jet supports the weight of the ball and as it moves off-center then Bernoulli means that there is a low pressure on the jet side of the ball that draws it back in. This is often unsatisfying as an e ..read more

Here is a link to a video from the “Solid body rotation – measuring the rotational velocity of a potting wheel” demonstration. The video shows the parabolic cavity forming as the water spins up until a steady solid body rotation is achieved. In this video the wheel was slightly wobbly so the cavity was not perfectly parabolic. An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkay ..read more

This demonstration uses the pressure distribution in a fluid undergoing solid body rotation to estimate the rotational speed of the cylinder. Pre-demonstration calculations Under solid body rotation about a vertical axis the horizontal variation in pressure in the radial direction is dP/dr=-ρa=ρω2r The pressure in the vertical direction is also hydrostatic resulting in the free surface at the top of the water becoming curved concave up. Taking the origin to be at the free surface on the axis of rotation then the pressure along a horizontal radial line from that point will be P=ρω2r2/2 such tha ..read more

Here is a link to a video from the “‘Rotational buoyancy’ update – potting wheels and fishing tackle” demonstration. The video shows the buoyant float moving toward the center of the jar while the weight moves out to the side of the jar. An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on impr ..read more

Introduction My 7 year old daughter has been learning about states of matter in school and had to do an experiment to see if gasses have mass. The experiment involved balancing 2 inflated balloons on either end of a stick and then popping one of them. The idea being that, because all the air escapes from the popped balloon, the un-popped balloon will be heavier (because of the weight of air inside the balloon. The video of her experiment is linked here. I posted this in my junior level fluid mechanics class discussion board and asked my students if this was a valid experiment to show that gas ..read more

Many science museums have demonstrations in which a ball is levitated by an air jet. Typically the ball is quite light and the air jet quite broad. These setups can produce reasonably stable results with the ball staying supported by the air jet. They even work when the air jet is inclined. There are occasionally explanations associated with the demonstration talking about how the drag from the air jet supports the weight of the ball and as it moves off-center then Bernoulli means that there is a low pressure on the jet side of the ball that draws it back in. This is often unsatisfying as an e ..read more