Density and Pressure
You’re probably under enough pressure as it is, cramming in revision for your exams. Here’s a page about a different kind of pressure, the one exerted by an object over a particular area. Read on to find out how to calculate the density and pressures of different materials..
Density
Density is a measure of the mass per unit volume of an object and is represented by the symbol rho (ρ). A golf ball is more dense than a beach ball since it has more mass in a smaller volume. The density of an object will determine whether it floats or sinks in water - anything more dense than water will sink while anything with a lower density will float. The density of an object depends on the material it is made from so it won’t vary if the shape or size of the object changes. The density of an object can be calculated by dividing the mass (in kg) by its volume (in cubic meters).
Pressure
Pressure is a measure of the force per unit area. The same force applied to a smaller area will result in a greater pressure. This is why it hurts so much to step on a pin, because a lot of force is concentrated in a single area. Pressure can be calculated by dividing the force (in Newtons) by the area (in meters squared).
The pressure within a liquid increases with depth from its surface. This is because the fluid particles at the bottom of a container have the added weight of the particles on top of them, which creates more pressure on the particles on the bottom. This is easy to imagine if you think of the particles as people in a human pyramid. If the pyramid collapses, the people on the bottom are going to feel more force (pressure) compared to the people at the top of the pyramid.
Imagine a bucket filled with water which contains holes at the top and bottom of the bucket. Water escaping from holes at the bottom of the bucket will travel further since it is subject to greater pressure (due to its greater density) so it leaves the bucket at greater force.
Pressure difference
Whenever we measure the pressure of a gas or a liquid (for example, when measuring the pressure of bicycle types), then we are actually measuring the difference in pressure compared to the pressure of gases in the air (atmospheric pressure).
A device called a manometer can be used to measure the pressure of a fluid. It consists of a U-shaped tube filled with liquid. The height of the liquid on either side of the tube can be used to determine the pressure difference using the following equation:
Did you know…
Everyone knows that the last place you’d expect to eat delicious food is on an aeroplane. One of the reasons for this is that the low pressure and humidity in an aircraft reduce our ability to taste food properly. Our sensitivity to sweet and salty flavours drops by about 30% when we’re at high altitudes. Of the five senses, only our taste for umami is heightened. Image credit: Ruth Fremson / NYTimes
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