mechanics Flashcards
what is newtons second law of motion?
F = MA
force (N)
Mass (Kg)
acceleration (m/s2)
what is the accelaration of gravity?
9.81 m/s2
what is the force of a 20kg object held above ground?
accelaration of gravity = 9.81
f=ma
f = 20x9.81 = 196.2 N
what is a newton in SI units?
kg x m/s2
what is inertia?
if an object is stationary or moving at constant velocity it tends to resist changes to its motion.
hence force needs to be applied for acceleration/ deceleration.
newtons 1st law of motion
how much in grams is 1 newton of force equivalent too (i.e. based on gravity)
1 N = 10.2g of force
what is the equation for momentum?
momentum = mass x velocity
what is the law of conservation of momentum?
The momentum of all objects before the collision = the momentum of all objects after collision
(provided there is no net external forces acting on object)
e.g. 2 balls collide - total momentum after = total momentum before.
what is newtons first law of motion?
in absence of external forces an object will remain at rest or constant velocity.
i.e. inertia
(requires driving force or friction for acceleration/ decelaration)
what is newtons 3rd law of motion?
for every force there is equal and opposite force acting on an object.
what is the formula for pressure derive the SI units…
force / area
measured in pascals
N/m2
N= kgms-2
therefore
Kgms-2/m-2
= kgm-1s-2
a balloon is filled with air at a force of 10N. 4 holes are made each of 0.05m2. what is the pressure of the air leaving the balloon?
all wall of the balloon will exert equal pressure of 10m2
the pressure leaving will be equal in all holes
0.05x4 = 0.2
10/0.2 = 50 pascals
50/4 = 12.5 pascals per hole
how can you manipulate the syringe you use to give more pressure?
A smaller syringe gives higher pressure because same newtons of force over smaller area.
alternatively to push a larger syringe it may need more force to create the same amount of pressure
how is the pressure in a column of liquid calculated?
Pressure = density of liquid x height (m) x accelaration of gravity
P= pgh
(in an angulated column, it is the vertical height that matters)
if this column is open to the atmosphere, the atmospheric pressure can be added on
P = pgh + atmP
or can add whatever other pressure may be exerted on the column.
how is force a column of liquid produces calculated?
pressure of a column = pgh
P=N/m2
therefore N= Pm2
so force = pgh x m2
what is the equation for work done?
work = force x distance
work = pressure x volume
- e.g. how much energy needed to push a column of pressure by a certain volum
what is energy?
the capacity to do work
measured in joules
what is the equation for power?
workdone / time
joules / second
derive joules as an SI unit…
force x distance
N = kgm/s-2
distance = m
kg.m2.s-2
how does a hydraulic lift work?
workdone can be transferred from one unit to the next
imagine 2 columns of liquid -
work done = force x distance
first column has minimal force needed as small cross sectional area however is pushed down over a large distance
this can lift the other larger column (larger cross sectional area) over a small distance in height.
how do airbags and seatbelts work?
air bag increases contact surface - this will reduce the pressure.
pressure = N/m2
seat belt will increase the stopping distance due to stretch.
joules energy = N x m2
joules/ m2 . the larger the stopping distance the less force exerted on body at one time i.e. discipitated over a larger distance.
what is the difference between gauge pressure and absolute pressure?
gauge pressure = pressure relative to atmosphere. i.e. when a cylinder of gas is empty, gauge pressure reads 0
absolute pressure = gauge pressure + atmospheric pressure
what type of pressure is blood pressure?
gauge pressure - relative to atmospheric
define force…
vector quantity i.e. has magnitude and direction
which can be applied to an object to cause it to accelerate/ decelerate
Are you more likely to dislodge a
blockage in a cannula when using
a 2 or 20 mL syringe?
a 2 ml syringe, as pressure is force over area. the 2 ml syringe has a
smaller cross-sectional area so the force applied by the thumb is spread
over a smaller area generating a higher pressure.
is atmospheric pressure constant?
no.
atmospheric pressure is created by the force of gravity acting on the
molecules that make up the atmosphere
therefore atmospheric pressure
will depend on the height of the atmosphere and its density.
this means atmospheric pressure will fall with altitude and rising temperature.
