Mechanics and Pressure Flashcards
What is Newtons 1st law of motion?
In the absence of external forces: an object at rest remains at rest, an object in motion continues in motion at a constant velocity.
Inertia is the term used to express this law.
What is the formula for momentum?
P=mv
P=Momentum
M=Mass
V=Velocity
What is the relationship between mass and inertia?
The greater the mass the greater the inertia. (More force is required to move heavier objects)
What is Newton’s second law of mortion?
Newton’s second law of motion
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
F=ma
F= force
m= mass
a= acceleration
Define weight?
Weight is the force with which an object is pulled towards earth by gravity.
As its is a force technically it should be expressed in Newtons
The force of gravity acting on an object gives it what acceleration?
9.81m/s
Therefore a 1kg object under the influence of gravity has 9.81N of force.
What is Newton’s third law of motion?
For every action there is an equal and opposite reaction.
Take a collision between two objects: the action and reaction forces involved in the collision result in a change in velocity of both the objects, which in turn changes the momenta of these objects.
Car A weighs 3500kg and is travelling at 20m/s. Car B weighs 1500kg and is stationary.
Car A crashes into Car B. Car Bs new velocity is 14m/s. What is Car A’s velocity post crash.
Momentum before and after collision must be equal (law of conservation of momentum).
3500 x 20 = 70000
1500 x 14 = 21000
70000 - 21000= 49000
49000/3500 = 14
Therefore Car A’s velocity post crash will be 14m/s
Define 1 Newton?
A newton is the force that gives a mass of 1 kg an acceleration of 1 m/s2.
What is the formula for Pressure?
Pressure=Force/Area
What is the equivalent pressure of 1atmosphere in: Pascal, KPa, Bar, cmH2O, mmHg?
1 atmosphere = 1.013 bar = 101.3 KPa = 101300 Pascal = 1020cmH2O = 760mmHg
When trying to unblock the lumen of a tube you have the choice of a 2ml or 10ml syringe with which syringe are you more likely to unblock the lumen and why?
You are more unlikely to unblock the lumen with a 2ml syringe as the force applied will be over a smaller area and therefore will exert more pressure.
Pressure = force/area
Explain how a pressure relief valve works in an anaesthetic machine?
Gas is flowing through a pipe, there will be an offshoot pipe with a pressure relief valve.
As gas flows through the offshoot pipe it will exert a pressure on the valve. The valve is held down by a spring.
If the upward pressure in the offshoot pipe exceeds that of the spring then the valve will be pushed up an open allowing gas to escape and reducing the pressure.
Explain how a pressure reducing valve works in an anaesthetic machine? (drawing a diagram may help)
Gas from the cylinder enters via the high pressure inlet. It then passes into a chamber via a valve. The valve consists of a hole and a tapered plug on the end of a shaft.
The pressure from the gas in the chamber acts on a disc to create a force that tends to close the valve (reducing the pressure) by moving the occluding ball upward. This force is opposed by the downward force of a spring.
As pressure in the chamber falls the valve tends to open, whilst as the pressure rises the valve closes.
How do you calculate the absolute pressure in a cylinder of gas?
Gage pressure + atmospheric pressure
