Dr Hector Perera            London

When we think about pressure, one of the important pressures that comes to mind is, High blood pressure (HBP). This is a serious condition that can lead to coronary heart disease, heart failure, stroke, kidney failure, and other health problems. “Blood pressure” is the force of blood pushing against the walls of the arteries as the heart pumps blood.

What is blood pressure?

When your heart beats, it pumps blood round your body to give the body the energy and oxygen it needs. Pressure is needed to make the blood circulate. The pressure pushes against the walls of your arteries (blood vessels) and your blood pressure is a measure of the strength of this pushing combined with the resistance from the artery walls.

A normal heart pumps blood around the body easily, at a low pressure. High blood pressure means that your heart must pump harder and the arteries have to carry blood that’s flowing under greater pressure. This puts a strain on your arteries and your heart, which in turn increases your risk of a heart attack, a stroke or of suffering from kidney disease. You can’t usually feel or notice high blood pressure

Around a third of people in England have high blood pressure and many don’t know it. This is because high blood pressure very rarely causes any obvious symptoms. Has anybody got any statistical report about this condition among Sri Lankans? I am sure the medical journal is the place to visit for this information.

There isn’t always a clear explanation as to why someone’s blood pressure is high. However, there are several things that can play a part: regularly drinking too much alcohol, not doing enough exercise, being overweight, not eating a healthy diet that includes not enough fruit or vegetables in the diet, a family history of high blood pressure or consuming too much salt. The only way of knowing if there’s a problem is to have your blood pressure measured. You can have this done at your GP surgery, some local pharmacies, or you can buy a monitor from the pharmacy or the chemist.

Pressure in and around us

Some pressures in life are obvious. They are the outside ones. Piles of work in the office, a very demanding boss, deadline to beat, school or exam work, a nagging spouse. They are really temporary and manageable. A student may be pressured by both financial problems, and the submission of school project. When this happens he might get emotionally battered. Sometimes due to parental pressure boys or girls get married even when they are not like to that proposal. Especially Asians have these kinds of peer pressure.

There are many forms of pressure around us and also within us. The continuous physical force exerted on or against an object by something in contact with it. On a heavy rainy windy day, one would notice the trees and branches sway in the wind, leaves and branches and even trees fall down due to the pressure of wind. We cannot see the wind but one can feel the wind. Why a balloon expands when we blow to it, due to air pressure. Vehicles such as cars, vans, busses and lorries have tyres for movements but they have to have a certain pressure to drive off safely. Out of four wheels, if one tyre is either totally flat or with less air, it cannot move off easily. We inflate the tyres with a foot pump or go to the petrol garage to get it inflated, but how many us have you been to the doctor or the nurse to get the blood pressure checked? The doctors have recommended to get the blood pressure checked especially of older people but how many of them have really cared to do this simple blood pressure check-up, too busy?

Sometimes we get pressure or persuasion or intimidation to make someone do something. Parents want their children the best and they put some pressure on them to learn, avoid keeping company of the wrong kind of friends. Sometimes they cannot be done without some kind of pressure. I have noticed the behaviour of some children in my science lessons, honestly too much to mention over here. Sometimes I had to tell some students to stop behaving unacceptably such as when they swing around on one leg of a chair instead of sitting properly. Apart from the risk that the child will damage the chair or hurt him or herself, the chair leg can damage the floor. This is because it puts too much pressure on the floor. When sitting on one leg of a chair, it exerts more pressure than sitting on four legs. Pressure depends on the area in contact with the floor or something.

You cannot safely walk on a plank of wood with pointing nails on it because the nails in contact would exert greater pressure on the foot. To my surprise some devotees in Kataragama Devalyaya walk on fire, planks of wood with pointing nails and many more such amazing things.  I am sure there is no scientific explanation for these amazing actions. Drawing pins have a large round end for you to push. The round end has a large area, so it applies a low pressure to your thumb. The sharp end has a very small area. The same pushing force produces a high pressure. Objects float in water when their weight is balanced by the up thrust from the water. The object will sink until the weight of the water it pushes out of the way is the same as the weight of the object. When Archimedeans got into the bath, he noticed the water flow out equal to his body weight, then only he discovered the law of flotation. He was so surprised with the discovery, he forgot to cover his dignity and ran all the way to the palace saying, Eureka Eureka”.  When an object rests on a surface such as the ground, its weight is balanced by the reaction force from the ground. The ground pushes up against the object. The reaction force is what you feel in your feet as you stand still. Without this balancing force you would sink into the ground. You may easily stand up on both legs for a long time but try and see how long you can just stand on one leg, not easy.

 Frictional forces

Whenever an object moves against another object, it feels frictional forces. These forces act in the opposite direction to the movement. Friction makes it harder for things to move.

Helpful frictional forces

Friction can be useful: friction between our shoes and the floor stop us from slipping, friction between tyres and the road stop cars from skidding, friction between the brakes and wheel help bikes and cars slow down, Frictional forces are much smaller on smooth surfaces than on rough surfaces, which is why we slide on ice.

Unhelpful frictional forces

Friction can also be unhelpful. If you don’t lubricate your bike regularly with oil, the friction in the chain and axles increases. Your bike will be noisy and difficult to pedal. When there is a lot of friction between moving parts, energy is lost to the surroundings as heat. Think of what happens when you rub your hands together quickly. The friction warms them up.

Air resistance