Mechanical systems and control Flashcards
What is a mechanism?
A mechanism is a set of moving parts used to make work easier.
What is a lever?
A simple mechanism used to move weights by a bar that turns around a fixed point. Levers make moving, prying, lifting and shifting objects much easier.
What is a fulcrum?
The pivot on which the arm of a lever moves
How do levers work?
All levers have a rigid, straight arm that turns around a fixed point, called the fulcrum. The fulcrum can be anywhere along the arm.
What is the effort?
The force exerted in a mechanism that enables it to work e.g. a hand pulling a bottle top opener.
What is the load?
The weight/mass that needs to be lifted, cut or moved.
Name the three types of levers and the differences between them.
First class levers - fulcrum in the middle - effort is in the opposite direction to the load. (FEL) Second class levers - load is in the middle - effort is in the same direction as the load (FLE or ELF) Third class levers - effort is in the middle - effort is in the same direction as the load. (LEF)
What is mechanical advantage?
When a mechanisms allows us to move a large load with a small effort. It is determined by the length of the bar, the position of the fulcrum and the position of the force and the load.
What are load and effort measured in?
Newtons
Is there mechanical advantage in first class levers?
It depends on where the fulcrum is positioned. If the fulcrum is positioned close to the load and the distance between the fulcrum and the effort is bigger, there is Mechanical advantage. If the fulcrum is in the centre between the load and the effort and the two are balanced there is no mechanical advantage.
How do you calculate mechanical advantage?
MA = load/force. The greater the MA, the more the lever helps you.
Is there mechanical advantage in second class levers?
Yes but requires increased effort.
What will improve the mechanical advantage of a second class lever i.e. moving a large load with small effort?
If the load is very close to the fulcrum
Give me an example of a first, second and third class lever.
First class lever: See Saw Second class lever : Wheelbarrow Third class lever: Human arm
IS there mechanical advantage in third class levers?
No. The effort must always be greater than the load.
What are the advantages of third class levers?
They can move a load a long distance relative to effort.
They are easy to use.
What are linkage systems?
Two or more levers that are joined together
What are two joined levers called?
Paired levers
Where is the fulcrum usually positioned with paired levers?
The fulcrum is where the two levers join.
What is the advantage of linked third class levers?
They allow us to make precise and accurate movements.
What is a complex linkage?
It is made up of a number of levers joined together e.g. a security gate.
What are linkages used for?
Change the direction of a movement
Change the distance of a movement
Allow parts to move in parallel with one another
Allow two or more items to move at the same time.
What is a pneumatic system?
A mechanical system that uses compressed air to give us mechanical advantage for tasks.
Define a force
An effort that can move an object usually a push or a pull.
Pneumatic systems are open systems. What does this mean?
An open system lets something like air in or out.
What is a hydraulic system?
A mechanical system that uses liquids under pressure to give us mechanical advantage.
Hydraulic systems are closed systems. What does this mean?
A closed system contains a fixed amount of the substance e.g. liquid under pressure and does not allow any of the substance in or out.
Do hydraulic systems provide high or low mechanical advantage?
Very high mechanical advantage because liquid cannot be compressed so pressure on the liquid produces an immediate output response.
Give me an example of a pneumatic system.
Bicycle pump, dentist drill
Give me an example of a hydraulic system.
Car braking systems
