Post on 27-Dec-2015
In science and technology work is done when a force acts on a body and the body moves in the direction of the force.
No work is done Work is done
Work = Force x DistanceOR
W = F x d
If you don’t move the object, no work is done!!!!!!!!!!!!!!
Is work being done?
The SI unit for both work and energy is the joule.
1 Joule = 1Newton x 1 meterOR
J = N x m
Power – The rate at which work is done
Power can be defined as:
Power = Work Time
P = w/t
Energy is the ability to do
work!
The SI unit for energy is the
joule.
There are several types of energy:
PotentialKineticChemicalNuclearRadiant (Heat)
Mechanical Energy - Energy due to the position of something or the movement of something.
It can be in the form of kinetic or potential energy or the sum of both.
ME = KE + PE
Potential Energy Stored energy (ex: stretched spring, drawn bow, coal).
There are several types of potential energy:
1) Elastic potential energy
2) Chemical potential energy
3) Gravitational potential energy is due to an objects elevated position.
Gravitational potential energy can be calculated using the formula:
GPE = mgh
Where m = mass, g = the gravitational constant of 9.8m/s2, and h = the height of the object.
Kinetic energy is energy of motion. All moving objects have kinetic energy.KE = ½ mv2
Law of conservation of energy – Energy cannot be created or destroyed. It can only be transformed into another form of energy.
Law of conservation of energy – Energy cannot be created or destroyed. It can only be transformed into another form of energy.
A machine is a device that multiplies and changes the direction of the force.
Machines make work easier by:
1) increasing the force that can be applied to an object
2) Increasing the distance over which a force can be applied
3) Changing the direction of force
The most basic machines of all are called simple machines.
There are six types of simple machines that are divided into two families, the lever family and the inclined plane family.
Lever – all levers have a fulcrum (pivot point).
There are three types of levers.
• 1st class lever • 2nd class lever • 3rd class lever
1st class lever – fulcrum is in the middle, the input force acts on one end and the other end applies an output force (hammer, sea-saw)
The fulcrum is in the middle.
2nd class lever – fulcrum is at one end of the arm and the input force is applied to the other end (wheelbarrow, hinged doors)
The output is in the middle.
3rd class lever – multiplies distance instead of force (human joints – elbow, knee)
The input is in the middle.
Pulley – used to lift things. Using more than one pulley or movable pulleys increase efficiency.
Fixed Pulley – The pulley is attached to something that does not move.
Moveable Pulley – One end of the wheel is fixed and the pulley is free to move.
Multiple pulleys are sometimes called a block and tackle.
Wheel and Axle – is made of a lever or a pulley (the wheel) connected to a shaft (the axle).
When a small input force is applied to the axle, the force is multiplied to become a large output force applied to the wheel (steering wheel, screwdriver).
Inclined Plane (Ramp) – turns a small input force into a large output force by spreading the work out over a large distance.
Wedge – two inclined planes back to back, it turns a single downward force into two forces directed out to the sides (wood splitter, nails).
Screw – is an inclined plane wrapped around a cylinder, it requires a small force acting over a large distance (jar lids, spiral staircase).
A machine that combines two or more simple machines is called a compound machine.
Mechanical Advantage=input distanceoutput
distance
Mechanical Advantage= Output Force Input Force
Mechanical Advantage:
A machine with a mechanical advantage of 1 or greater multiplies the input force
A machine with a mechanical advantage of less than 1 does not multiply the input force but it does increase the distance and/or speed.
What is efficiency?
Efficiency is a measure of how much of the work put into a machine is changed into useful output work.
Calculated using the following formula:
Efficiency % = output work (J) x 100% input work (J)