KS3 Physics - Pressure

In today's video we're learning about pressure. So we'll cover what pressure is and also how to calculate pressure. Let's begin with what pressure is. Pressure is essentially the amount of force that's applied over a specific area. For example imagine you're using a hammer to drive a nail into a piece of wood. When you strike the nail with the hammer you're applying a force to the head of the nail and this force is then transferred through the nail and concentrated at its tiny tip. The force, now focused on the small area of the nail's point where it contacts the wood, creates a really high pressure which makes it easier to push the nail into the wood. The smaller the area of the nail's tip, the higher the pressure it exerts on the wood at the point of contact. Another example is pressing your hand against a wall. The force you apply is spread out over the fairly large area of your hand as it touches the wall, so there's a fairly low pressure. But if you press with just one finger, the same force is applied over a smaller area, so there's a much higher pressure. It's important to note here though that the force is always perpendicular to the surface that it's acting on. This means it's acting at a 90 degree angle, sometimes called a normal, from the surface. So now let's take a quick look at how to calculate pressure. As we already know, pressure is the amount of force applied over a specific area, or in other words it's the force per unit of area. We can put this into an equation as P equals F divided by A, where P is pressure measured in pascals or PA, F is force measured in newtons, and A is area which is measured in square meters. So if we take that all together, one pascal is effectively one newton per square meter of area. Let's go through a worked example. Suppose you have a force of 50 newtons acting on an area of 2 square meters. To find the pressure, you would substitute the values into the equation, so pressure equals 50 divided by 2, giving us 25 pascals. Sometimes though, you might need to rearrange the equation to find the force or the area instead. Suppose we know the pressure is 100 pascals and the area is 5 square meters, but we are asked to find the force. By rearranging our original equation, we get force equals pressure times area, and then substituting in our values, this gives us 100 times 5. So the force needed to result in this pressure over this area is 500 newtons. If you haven't heard yet, you can find all of our videos on our website, cognito.org. You'll also find questions, flashcards, exam-style questions, and past papers, and we track all of your progress so that you always know what to study next. So sign up for free by clicking here, or browse our playlist here on YouTube.