Pressure is the amount of force pushing on an area. So if we have a small area, like the tip of a needle, and a lot of force behind it, we have high pressure. If we have a larger area, like the sole of a shoe, and the same amount of force, we have lower pressure. Pressure affects all kinds of systems, from the air pressure in our tires to the blood pressure in our bodies. Atmospheric pressure, which is the pressure of the air around us, changes with elevation and it’s why we need to pop our ears when we fly in an airplane.