p1.3-Pressure Flashcards
p1.3.1-Why do gases exert pressure?
When you blow up a balloon, it gets bigger and the number of air particles increase meaning more particles colliding. Each collision produces a small force and there are many collisions, each producing an outward force over a certain area. This produces a gas pressure.
p1.3.1-How does temperature affect gas pressure?
If the temperature of a gas increases, the gas particles have a higher average speed. They collide more frequently with the sides of a container and the collisions produce a bigger force over a certain area. This produces a bigger pressure. If you decrease the temperature, the pressure also decreases.
p1.3.2-How are pressure and volume related and what equation links them?
As the volume doubles, the pressure halves and other way around. This means pressure and volume are inversely proportional. The collisions of the gas particles produce a force that is at right angles to the surface. If you halve the volume, you double the number of collisions per second between the gas particles and container.
equation: pressure(Pa) x volume(m3) = constant(Pa m3)
P1.3.2-How does doing work on a gas affect the temperature?
The internal energy of a gas increases by you heating it or doing work on it. If you apply force to a bike pump, you do work on a gas and it gets hotter. The average speed of the particles increases because the kinetic energy increases when they collide with the moving piston, so the temperature is higher.
P1.3.3-What is a simple model of the Earths atmosphere?
The atmosphere protects the earth. The thickness of the atmosphere is very small compared with the diameter of the earth. The atmosphere is a single layer of gas that covers the earth to a height above 700Km. In the simple model, it is assumed that the density of the atmosphere is the same in all parts of the atmosphere.
P1.3.3-What is atmospheric pressure?
Atmospheric pressure is exerted from the gases of the atmosphere and you can see the air is exerting a pressure by looking at what happens when you remove it. In an open can, the forces are equal in all directions so the shape doesn’t change and it collapses if you pump air out of the can.
p1.3.3-What happens to atmospheric pressure as you go up?
As you go away from the surface of the earth, the pressure decreases as there is less air above pushing down. For a 1m thick layer of air 1km away from earth, there is a pressure difference between the top and bottom of the layer because there is more air pressure at the bottom. The layer doesn’t move as upwards force balances weight of the air above it, pushing down.
p1.3.4-What is liquid pressure?
Liquid pressure is when the water molecules are closer together, colliding with each other or the container and acting in all directions. Deeper water has more pressure as molecules in a layer are compressed by weight of the liquid above the layer. This pushes water molecules together, thus increasing the pressure.
p1.3.4-What happens to pressure in liquids of different densities and the equation for it?
There is always a higher amount of pressure in a higher density liquid. This is because there is a greater weight of liquid pushing down in a denser liquid. The pressure due to a column of mercury is bigger than the pressure due a column of water.
equation: Pressure(Pa) = height(m) x density(kg/m3) x gravitational field strength(N/kg)
p1.3.5-Why is there an upwards force on a floating object?
Anything that is floating must have an upward force on it to balance its weight. In a pool, the upthrust comes from the water exerting an upwards force and air exerting a downwards force with the net force being upwards.
An object floats if: (pressure at bottom X area at bottom) - (pressure at top X area at top) = weight
p1.3.5-How do you calculate depth?
depth(m) = weight(N) / density(Kg/m3) X gravitational field strength(N/Kg) X area(m2)
weight(N) = mass X gravitational field strength
p1.3.5-Why do some objects float and others sink?
If the pressure difference and area is big enough, the net force will be enough to balance its weight. To make a submarine sink, you would need to increase the weight by letting water into it. To make it float again, you would need to pump air into the tanks and submarines carry tanks of compressed air for this.
