Energy, Work and Machines Review
Energy and Work
· Energy is the ability to make something happen
· There are two basic kinds of energy- potential energy and kinetic energy
· Potential energy is stored energy
· Kinetic energy is energy of motion
· There are six main forms of energy-
1. Mechanical
2. Electrical
3. Electromagnetic
4. Heat
5. Chemical
6. Nuclear
· Gravitational Potential Energy depends on the weight an object has and how high the object is ( how far it has to fall), PE = weight x height
· Energy can change from one form to another
· When energy changes form, some of the energy is always changed into heat energy
· Thermal pollution is the damage that occurs when waste heat enters the environment
· The Law of Conservation of Energy states that energy can never be created or destroyed but only change form
· The total amount of matter and energy in the universe never changes
· Work is done when a force moves an object
· For work to be done, the direction of the applied force must be the same as the direction of motion
· Work = F x D
· Work can be measured in Newton-meters (N-m)
· The unit of work is the joule (J); 1 J= 1 N-m
· When measuring work, you must measure the force applied in the direction of motion.
· Power is the amount of work done per unit of time
· Power = work/time, or force x distance/ time
· The SI unit of power is the watt (W)
Machines
· Machines make work easier by changing the size, direction, or speed of a force
· The force you apply to a machine is the effort force, and the force that opposes the effort force is the resistance force
· Mechanical Advantage is the number of times a machine multiplies the effort force. It is equal to the resistance force divided by the effort force.
· MA = RF / EF
· RF = MA x EF
· EF = RF / MA
· Resistance force and Effort force are measured in Newtons
· Mechanical Advantage has no units
· The ideal mechanical advantage is the mechanical advantage that a machine would have with no friction
· There are six kinds of simple machines:
1. Lever
2. Pulley
3. Inclined plane
4. Wheel and axle- two different sized wheels that turn together around the same point
5. Screw
6. Wedge
· Efficiency is the ratio of work output and work input
· Work output is the work done by a machine
· Work input is the work done on a machine
· Work output = resistance force x resistance distance
· Work input = effort force x effort distance
· Percentage efficiency = work output / work input x 100
· Lever is a bar that is free to turn around a fixed point. It has 2 parts: the effort arm and a resistance arm.
· Levers are divided into three classes according to the position of the effort force, the resistance force and the fulcrum
· The IMA of a lever is effort arm length/ resistance arm length
· Pulley is rope wrapped around a wheel
· A fixed pulley is attached to something that does not move
· Fixed pulleys change the direction of the effort force
· The IMA of a fixed pulley is equal to 1
· Moveable pulleys can move as the rope is pulled
· A moveable pulley does not change the direction of the effort force but increases the size of the effort force
· A pulley system is made up of both fixed and moveable pulleys
· An inclined plane is a slanted surface or a ramp
· The IMA of an inclined plane is equal to its length divided by its height
· A wedge is often two inclined planes back to back. A screw is an inclined plane wrapped around a cylinder
· A compound machine is composed of two or more simple machines
Formulas
· Gravitational PE = weight x height
· Work = F x D
Units in Joules
· Power = work/time, or force x distance/ time
Units in Watts
· MA = RF / EF
· RF = MA x EF
· EF = RF / MA
Resistance force and Effort force are measured in Newtons
Mechanical Advantage has no units
· Work output = resistance force x resistance distance
· Work input = effort force x effort distance
· Percentage efficiency = work output / work input x 100