P11: Force and pressure Flashcards
What happens to gas particles in a container?
They bounce off the container and exert a small force upon doing so. The force acts at right angles to the container (along the normal)
What is the formula for pressure exerted by fluids?
Pressure = Force normal to surface / Area of surface
Pa N m^2
Describe the ‘density’ of the atmosphere relative to the surface of the Earth
Most dense around the surface of the Earth (greater number of air molecules in a given volume). It gets less dense with increasing altitude
Why is the atmosphere more dense at the surface of the Earth?
Pressure is caused by the collisions of air molecules with the surface of the Earth. Therefore, as the surface increases hight above ground level, the number of air molecules above the surface decreases.
How does the pressure of water in a vertical container differ with height?
Water at the bottom has higher pressure than the water at the top.
What is the formula for the pressure of a column of liquid? (given)
P = hpg
Pressure = heightdensity of liquidgfs
Pa m kg/m^3 N/kg
Why does the pressure of a liquid change along a vertical column?
As depth increases, there is a greater weight of the liquid acting downwards, so pressure increases.
Liquids with greater density also increase pressure, as they have a greater depth acting downwards.
What is upthrust?
A resultant force acting upwards
What conditions are required for an object to float?
The object’s weight must be equal to the object’s up thrust.
How is the size of upthrust determined?
Equal to the weight of water displaced by the object (when lowering it into water).
- if the object can displace its own weight of water, then upthrust will be equal to it’s weight and the object floats.
