pressure

• What does the packet of crisps on board an airplane demonstrate?

  The effect of changing air pressure
• In a gas, how are the particles spaced?

  Widely spaced
• What is the movement of particles in a gas described as?

  Rapidly moving
• When gas particles collide with the walls of a container, what do they exert?

  A force
• In what direction does the force exerted by gas particles act on the wall?

  At right angles to the wall
• What term is used to describe the direction of force exerted at right angles to the wall?

  Along the normal
• What is exerting a force at right angles to the walls of a container also true of?

  Liquids
• What term do scientists use to refer to both gases and liquids?

  Fluids
• What is the unit of pressure?

  Pascal
• What is the pressure of the atmosphere?

  A thin layer of air around the earth
• Where is the atmosphere most dense?

  At the surface of the Earth
• What happens to the atmosphere's density as altitude increases?

  It gets less dense
• What causes atmospheric pressure?

  Air molecules colliding with a surface
• What happens to the number of air molecules above a surface as height increases?

  The number of air molecules decreases
• What happens to atmospheric pressure as height increases?

  Atmospheric pressure decreases
• Why do mountain climbers often take oxygen supplies?

  Air pressure is too low to supply oxygen
• What happens to air pressure in an airplane cabin compared to ground level?

  It is kept at a slightly lower level
• What is the air pressure inside a crisp packet at ground level compared to outside?

  The same
• Why do crisp packets inflate in airplanes?

  Air pressure inside is greater than outside
• In the demonstration with holes in the container, why does water squirt further from the bottom hole?

  The water at the bottom is at higher pressure
• Why does the pressure of a liquid increase with depth?

  There's a greater weight of liquid acting downwards
• Why does the pressure of a liquid increase with the density of the liquid?

  Liquids with greater density have greater weight
• What must be true for an object to float?

  Upthrust must equal the object's weight
• What happens if the upthrust is less than the object's weight?

  The object sinks
• When an object is lowered into water, what happens to the water level?

  The water level rises
• What is the relationship between the size of the upthrust and the weight of water displaced?

  They are the same
• If an object displaces its own weight of water, what will happen?

  The object will float
• How much water does an object with the same density as water have to displace to float?

  Its own volume of water
• For an object more dense than water, how does its weight compare to the upthrust?

  Weight is greater than upthrust