What is Machine?
Machines are devices by which work can be done easily. Examples of machines are , hammers, scissors , wheel barrow , pulley, Crowbar or anything at all that can help you do your work at ease.
Terminology of simple machine
- Mechanical advantage: it is defined as the ratio of load to the Effort, that is
where M.A = mechanical advantage, L = Load, and E = effort. Mechanical advantage depends on part on friction and the construction of the machines. So the smaller the friction the smaller the Effort and larger the mechanical advantage.
- Velocity Ratio (V.R) of Machine: it is defined as the ratio of distance moved by the Effort to the distance moved by the load, that is
where X = distance moved by Effort, Y = distance moved by the load and V.R = Velocity Ratio.
- Efficiency : It can be defined as the ratio of work output to work input, that
where Ɛ =n Efficiency. Efficiency can also be give as
The above equation can be used to solve problems, but it is not a basic definition of Efficiency. The equation is only the relationship between Efficiency, M.A and V.R
Classification of Machines
Machines can be classified into, FIRST ORDER LEVER, SECOND ORDER LEVER AND THIRD ORDER LEVER, MACHINES. The position of Fulcrum Effort and Load determine whether a Machines are First, Second or Third Order.
- First Order Lever Machine: IThey Machines that have their Fulcrum (where It is pivoted or supported) in between the Effort and the Load Example – Claw Hammer, Pliers, and Crowbar.
- Second Order Lever: It is the type of that has it load in between the Fulcrum and Effort. Example. Nutcracker, Wheel Barrow, etc.
- Third Order Lever Machine: This is the type of that has its Effort in between The Fulcrum and Load. Example – Fore-arm, Tongs etc.
Friction in Machines
Friction can be defined as opposing force which act at the surface of separation of two bodies in contact. Friction opposes motion. It depends on the nature of the surface in contact, but not on the area in contact. The Frictional Force can be give as
F = ɥR
Where μ = Coefficient of Friction, R = the reaction of weight in contact which is equal and opposite and F = Frictional force
The reaction R can also be give as
R = Mg, where M = mass of the body, g = acceleration due gravity
How to reduce Friction
- By using ball and roller bearing
- Using lubricating oil
- By streamlining
- By smoothing and polishing
Advantages of Friction
- It makes walking and running on ground possible
- It enable vehicle to stop
- It converts Mechanical energy to Heart energy.
Disadvantages of Friction
- It opposes motion
- It reduces the Efficiency of machine
- It causes wears and tears in Machine’s moving parts
- It causes unwanted heat
- A Machine with V.R 5 requires 1000j of work to raise a load of 500N through a vertical distance of 1.5M. Find the Efficient and M.A of Machine
- A machine has a velocity Ratio 5 and is 80% Efficient. What Effort would be needed to lift a Load of 2000N with the aid of this Machine
M.A = 3.75
But Ɛ = 80%
Effort required = 500N