P8-P11 Flashcards
What is meant by the term ‘fluid’?
A liquid or a gas.
In any fluid, at what angle do the forces
due to pressure act on a given surface?
At right angles (normal to) the surface.
State the equation used to calculate
pressure. Give appropriate units.
Pressure = Force/Area
Pressure (Pascals), Force (Newtons),
Area (metre²)
What happens to the density of the
atmosphere with increasing altitude?
The atmosphere becomes less dense as
altitude increases.
Explain why atmospheric pressure
decreases with an increase in height.
● Pressure is created by collisions of air
molecules
● The quantity of molecules (and so weight)
decreases as the height increases
● This means atmospheric pressure decreases
with an increase of height
What is the Earth’s atmosphere?
A thin (relative to the magnitude of the
Earth) layer of gas surrounding the
Earth.
How does pressure in fluids increase
with depth?
As the depth increases, the mass of liquid
above that depth also increases. This means
that the force due to the mass increases.
Since the force has increased whilst the area
has remained constant, the pressure will
increase.
Why does pressure in fluids increase
with density?
As the density of a fluid increases, the number of
particles in a given volume increases.
Consequently the weight of the fluid is greater.
This means that the force from the fluid above a
certain point is larger. Since the force has
increased, the pressure also increases.
What equation shows the magnitude of
pressure in liquids at different depths?
Pressure due to a column of liquid(Pa) =
Column height(m) x density(kg/m³) x
gravitational field strength(N/kg)
P = hρg
Why are objects in a fluid subject to an
upthrust?
Why are objects in a fluid subject to an upthrust?
When an object is submerged in a fluid, it has a
higher pressure below it than it does above, as there is more weight above it at the bottom than there is at the top. This leads to an upwards force called upthrust. You float or sink depending on whether the
upthrust is more or less than your weight.
What is upthrust always equal to?
The weight of the fluid that the object
displaces.
What factors influence whether an object
will sink or float?
● Upthrust
● Weight
● Density of fluid
Explain why an object with a density
greater than that of water can never
float.
Upthrust is equal to the weight of the displaced
fluid. If the density of the object is high, there
would not be enough volume displaced to
produce an upthrust larger than the object’s
weight. This means that it will sink.
Does a distance quantity require a
specific direction? i.e. Is it a scalar or
vector quantity?
No specific direction is required so it is a
scalar quantity.
If an object moves 3 metres to the left
and then 3 metres back to its initial
position, what is the object’s total
displacement?
● The object has zero displacement
● Displacement is a vector quantity so it also
involves direction
● The object starts and ends at the same point
State the equation linking distance,
speed and time. Give appropriate units.
Distance = Speed x Time
Distance (m), Speed (m/s), Time (s)
Why can an object travelling at a
constant speed in a circle not have a
constant velocity? (Higher)
● Speed is a scalar quantity
● Velocity is a vector quantity which means it can
only be constant if the direction is constant
● In circular motion, the direction is continuously
changing
How can speed be calculated from a
distance-time graph?
The speed is equal to the gradient of the
graph.
What must be done to calculate speed at
a given time from a distance-time graph
for an accelerating object? (Higher)
● Drawing a tangent to the curve at the
required time
● Calculating the gradient of the tangent
State the equation for the average
acceleration of an object. Give
appropriate units.
Acceleration = (Change in Velocity)/(Time
Taken)
Acceleration (m/s²), Velocity (m/s), Time (s)
How can the distance travelled by an
object be calculated from a velocity-time
graph? (Higher)
It is equal to the area under the graph.
Give an approximate value for the
acceleration of an object in free fall
under gravity near the Earth’s surface.
9.8 m/s²
What can be said about the resultant
force acting on an object when it is falling
at terminal velocity?
● The resultant force is zero
● When at terminal velocity, the object is
moving at a constant speed and so
isn’t accelerating
State Newton’s first law for a stationary
object.
If the resultant force on a stationary
object is zero, the object will remain at
rest.
