BBC Bitesize - KS3 Physics - Pressure - Revision 1
Calculate the pressure. pressure = force ÷ area. = 20 N ÷ 4 m 2 = 5 N/m 2. Notice that the unit of pressure here is N/m 2 (newtons per square metre). Sometimes. He says "This area is completely different to the one above", but this means nothing. with your thinking is that you're not paying attention to the equation: the force F . Is Pressure of a perpendicular Force applied on the Area of a surface. Pressure and force are related, and so you can calculate one if you know the other the physics equation, P = F/A. Because pressure is force divided by area, .
How restrictive are the assumptions governing its use? Here we give some examples. The flow therefore satisfies all the restrictions governing the use of Bernoulli's equation. Upstream and downstream of the contraction we make the one-dimensional assumption that the velocity is constant over the inlet and outlet areas and parallel.
One-dimensional duct showing control volume.
When streamlines are parallel the pressure is constant across them, except for hydrostatic head differences if the pressure was higher in the middle of the duct, for example, we would expect the streamlines to diverge, and vice versa.
If we ignore gravity, then the pressures over the inlet and outlet areas are constant. Along a streamline on the centerline, the Bernoulli equation and the one-dimensional continuity equation give, respectively, These two observations provide an intuitive guide for analyzing fluid flows, even when the flow is not one-dimensional.
For example, when fluid passes over a solid body, the streamlines get closer together, the flow velocity increases, and the pressure decreases. Airfoils are designed so that the flow over the top surface is faster than over the bottom surface, and therefore the average pressure over the top surface is less than the average pressure over the bottom surface, and a resultant force due to this pressure difference is produced.
This is the source of lift on an airfoil. Lift is defined as the force acting on an airfoil due to its motion, in a direction normal to the direction of motion. Likewise, drag on an airfoil is defined as the force acting on an airfoil due to its motion, along the direction of motion.
An easy demonstration of the lift produced by an airstream requires a piece of notebook paper and two books of about equal thickness. Place the books four to five inches apart, and cover the gap with the paper.
When you blow through the passage made by the books and the paper, what do you see? Example 1 A table tennis ball placed in a vertical air jet becomes suspended in the jet, and it is very stable to small perturbations in any direction.
Pressure is Force per Unit Area
Push the ball down, and it springs back to its equilibrium position; push it sideways, and it rapidly returns to its original position in the center of the jet. In the vertical direction, the weight of the ball is balanced by a force due to pressure differences: To understand the balance of forces in the horizontal direction, you need to know that the jet has its maximum velocity in the center, and the velocity of the jet decreases towards its edges.
The ball position is stable because if the ball moves sideways, its outer side moves into a region of lower velocity and higher pressure, whereas its inner side moves closer to the center where the velocity is higher and the pressure is lower. The differences in pressure tend to move the ball back towards the center.
Example 3 Suppose a ball is spinning clockwise as it travels through the air from left to right The forces acting on the spinning ball would be the same if it was placed in a stream of air moving from right to left, as shown in figure Spinning ball in an airflow.Introduction to Pressure - Force & Area, Units, Atmospheric Gases, Elevation & Boiling Point
These types of shoes can cause damage to some floors due to the very high pressure on the floor at the heel. An average shoe distributes the weight of the person over 20 square inches. Since a spike-heel is only 0. In some cases, that is sufficient to damage the floor.
Fluid weight If you put a liquid in a container, the weight of that liquid would be pressing on the bottom of the container similar to that of the weight of a solid object. The pressure on the bottom of the container would be the same as if the weight was from a solid: The only difference is that pressure in a fluid goes in all directions.
So the pressure on the sides at the bottom would be the same. Gases and liquids exhibit pressure due to their weight at every point in the fluid.
fluid dynamics - Relation between pressure, velocity and area - Physics Stack Exchange
Summary Pressure is the force on an object that is spread over a surface area. Pressure can be measured for a solid is pushing on a solid, but the case of a solid pushing on a liquid or gas requires that the fluid be confined in a container. The force can also be created by the weight of an object.