pressure

• what is the equation for pressure?

  pressure = force / area
• in fluids (liquids+gases) what do particles do with the walls of their container?

  the particles collide with the walls of their container. The particle exert a force on the container and the container exerts a force on the particle.
• the force exerted on the surface in contact with the fluid particles will be at the normal to the surface (at right angles).
• why do our ears pop on a plane?

  because of the drop in atmospheric pressure.
• at the top of mountains, why is atmospheric pressure lower?

  because there is less air (fewer particles) pressing down on the mountain. Air is lighter than water, but it still exerts pressure on the things beneath it.
• what is pressure?

  the force per unit of area
• what causes bread to rise in the oven?

  when you put bread in the oven its temperature rises. The air particles in the bread have more kinetic energy and exert a pressure on the bread from the inside. This creates air bubbles that expand causing the bread to rise.
• we feel the weight od the atmosphere at what pressure?

  100 kPa
• what affect does temperature have on gas' kinetic energy?

  the higher the temperature of gas, the higher the kinetic energy stored in the gas' particles.
• as you heat a gas, what increases the speed of the particles?

  you are transferring more kinetic energy to the gas' particles.
• what happens when a gas particle collides with the wall of its container?

  its momentum changes and it bounces back off the wall. This exerts a force on both the particle and the wall.
• what is the equation for change in momentum?

  change in momentum = force x time
• what happens if you increase the temperature of a gas in a fixed volume?

  the particles will collide with the container walls with more force therefore the pressure will increase.
• what does the pressure of a gas produce?

  a net force (the sum of all the forces) at right angles to the wall of a container.
• doing work on a gas increases the gas' what?

  internal energy. This increases the temperature of the gas.
• what is the equation for momentum?

  momentum = mass x velocity
• what is the equation for liquid pressure?

  liquid pressure = density x GFS x depth
• why do you feel more pressure the deeper you swim?

  as you dive deeper there is more water on you, this extra weight exerts a larger force (and higher pressure) on your body.
• where will a partially submerged object feel more pressure?

  on the bottom surface rather than the top surface.
• what is upthrust equal to?

  upthrust = weight of liquid displaced
• what happens to the forces if the object's weight is equal to the upthrust?

  then the forces balance and the object will float in the water.
• when will an object sink?

  if an object's weight is greater than the upthrust.
• hen will an object float?

  if the object's weight is equal to the upthrust
• what happens when a submarine wants to come up to the surface?

  it fills its tank with compressed air to reduce its weight. Weight becomes less than upthrust so the submarine rises.
• what does a submarine do when it wants to sink?

  it fills its tank with water to increase its weight. This means the submarine's weight will be greater than the upthrust and it sinks.
• what do submarines use to control their depth in water?

  the balance between upthrust and weight.
• what is the equation for pressure difference?

  pressure difference = density of fluid x GFS x change in depth