I was sorting out the pressure on my van tyres. Pressure is out of fashion as a topic in school Physics at the moment. Pressure is force per unit area, and thus it would be measured in Newtons per square metre.
The reading above is in the old Imperial units of pounds per square inch. They are not really dimensionally correct as units because pounds is a measure of mass not force. But it does give a good mental picture of what's happening. That's about 30 bags of sugar balanced on a square inch - say on the area of a couple of 2p pieces.
Bar as a unit of pressure was introduced just over 100 years ago. 1 bar is roughly atmospheric pressure. 1 bar = 1000 millibars so air pressure in weather forecast is often given in millibars. A low pressure system might have a pressure of 980 mb, so not much below normal atmospheric pressure. My tyres were 4 1/4 times atmospheric pressure.
And finally to proper Physics units. KiloPascals. 1 Pa is 1 Newton per square metre. As you can work out, 1 bar = 100,000 Pa.
