Shanti Deemyad is an associate professor in physics in the University of Utah. Deemyad is an experimental physicist whose research is focused on studying matter at extreme conditions of pressure and temperature. Through the story of Shanti Deemyad, we’ll explore the physics of pressure.
After graduating from Sharif University of Technology in Iran, Shanti Deemyad received a PhD in Physics from Washington University in 2004. After that, she worked as a postdoctoral researcher (when you do more scientific research, after getting a PhD) at Harvard University. She is currently head of her own laboratory. Her group’s research interests include the synthesis of materials under high pressure and investigating new methods for high pressure research.
Most of our daily life experiences involve matter subjected to fairly moderate pressures. But once you start to ramp up the pressures some fascinating physics can start to occur, this is what physicists like Shanti Deemyad are working on. High pressures can be used to change the density of materials and therefore influence the interactions between atoms. Exotic physical phenomena can occur under these conditions, such as matter changing its form into metastable states – as is seen with the transformation of graphite (the materials in your pencil) into diamond – they’re both carbon!
Deemyad, who is an experimental physicist, uses different methods for achieving extreme pressures within a laboratory. One of those methods is known as a diamond anvil cell, which can be used to generate pressures as high as those in the Earth’s core.
What is pressure?
I’m sure you’ve been under pressure at some point in your life, doing exams or running late for a bus? This is how we would normally think of pressure, but a scientist thinks of pressure in terms of force applied and area its applied to. The unit of pressure is the Pascal (Pa) or newton per metre squared (N / m2). In physics, pressure is the amount of force acting over a unit area (Pressure = Force / Area). Imagine it’s Halloween and you are trying to carve a pumpkin, what would work best – a sharp knife or the dull edge of a spoon? Well the sharp knife obviously, this is because the knife has a smaller area. If it has a smaller area, then less force is needed. This is why elephants have such large feet, they have a bigger area to compensate for their massive weight. If elephants had skinnier legs, they’d get stuck in the ground!
Pressure in a liquid
We’ve looked at pressure in terms of solid objects, but there is also pressure exerted by liquids – and it’s a bit different to normal pressure. Pressure in a liquid is special in that it acts in all directions. It also gets bigger, the deeper in the water you go. The pressure at the very deepest part of the ocean is so high that only very special underwater equipment can be used to travel down there. Humans cannot withstand the pressures, you’d get crushed if you tried to swim down there.
Play around with this simulation and see how the pressure in a liquid can change depending on it’s density and depth!
Try at home!
Fill a plastic 2 litre bottle with water. Poke three holes along the length of the bottle with a thumbtack – one at the top, one in the middle and one at the bottom. What do you see happening?
Now, refill the bottle and turn it on its side, what do you notice now?
As well as solids and liquids, there is also pressure exerted by air. We call this atmospheric pressure and it acts in the same way as liquid pressure. The higher we go up into the air, the lower the pressure gets. When people climb very high mountains, the air gets so thin that they need a breathing apparatus to help them. We can measure air pressure using a barometer, a device that contains a column of mercury that reacts to pressure by changing its length. Normal atmospheric pressure here on earth is 760 mm of mercury, or in SI units 101,325 Pa.