Pressure (T5) Flashcards
What is pressure measure in on the SI system?
Pascals
Pa
Define pressure in physics and give an example..
The force per unit area.
Form example, a force applied to a large area, such as pushing someone with your open hand, could hurt less than the same force applied to the same person with the point of a nail.
The pressure at the point of the nail would be enormous due to the small area of contact, even though the force has not changed.
The pressure of 1 Pa is equal to…
1 N/m2
The difference in the pressure between two different depths in a liquid can be calculated by the following equation…
p = h x ρ x g
p = pressure in Pa h = height in m ρ = density in kg/m3 g = 9.81 N/kg
How does a submarine work with regards to pressure?
It must withstand the same pressure of water acting downward on its upper surface as the pressure acting inwards on the sides, or upwards on the bottom
How does pressure come into play in a car?
When you press down on your brake pedal you push in a piston in the master cylinder which increases the pressure in your brake fluid. This then exerts the same force at each of your four brakes, regardless of the direction in which the force is acting.
How do the forces of pressure behave when a balloon bursts?
A balloon explodes with equal force in all directions
Pressure in liquids acts equally in all directions, as long as the liquid is not moving. How could you demonstrate this with a household object?
By using a can with holes punched around the bottom. When the can is filled with water, the water is forced out equally in all directions.
Approximately what pressure is exerted on your body by the gases in the atmosphere around you? Why do we not notice this pressure exerted on us?
Around 100,000 Pa
The pressure inside our bodies is similar, so we do not notice the pressure of the air.
Describe one of the first demonstrations of the effects of air pressure, and explain how we can demonstrate this effect in a modern lab.
One of the first demonstrations of the effects of air pressure was carried out by Otto van Guericke in 1654, in Magdeburg, Germany. He had two large metal bowls made, put them together and then pumped the air out. The bowls could not be pulled apart, even when he attached two teams of horses to the bowls.
You can do the same experiment in the lab, using much smaller bowls called Magdeburg hemispheres. When air is inside the spheres, the pressure is the same inside and out. If the air is sucked out, pressure is only acting from the outside. The hemispheres cannot be pulled apart until the air is let back into them.
Why do gases exert a pressure?
Because of the combined effect of billions of collisions per second on anything they come into contact with. Each impact exerts a little force, but we experience a continuous pressure due to the huge numbers of molecules colliding with every square millimetre every second.
Pressure is the…
Force acting per unit area
In physics, how do you calculate pressure?
P = F / A
Where:
P = pressure in Pa F = force in N A = area in m2
