Work & Power How the world works…. Chapter 8 Objectives: I will identify what is work and what is not. I will calculate force and distance to measure the work.

Work or Not, Explain What is work?

Define / Describe WORK Work is done when a force causes an object to move in the direction that the force is applied. Object must move over a distance No movement = no work Work and Power Video Work:

Joules? Measured in Joules. Work Rule for Work Work (Joules) = Force (Newtons) X Distance(meters) W = F X d Example to calculate Work Question: A weightlifter raises weights of 2000 Newtons from the floor to a height of 2 meters. How much work has been done? Answer: W = F X d W = 2000 X 2 W = 4000 Joules Work

What is Power? Rate at which work is done. Power is measured in Watts. Power (Watts) = Work (Joules) / Time (seconds) P = W / T or P=(force x distance/ time) 1 W= 1 J/S (most common is 1 kilowatt) Example of calculating Power Question: A weightlifter lifted 2000 Newtons to a height of 2 meters. This 4000 Joules of work. What is the power output if this was done in 2 seconds? Answer: P = W / T = 4000 / 2 = 2000 Watts

More Power to You If it takes you 10s to do 150 J of work on a box to move it up a ramp, what is your power output? Answer: 15 Watts A light bulb is on for 12 s and during that time it uses 1,200 J of electrical energy. What is the wattage (power) of the light bulb? Answer: 100 Watts

Two things must happen for work to be done. A force must applied to an object The object must move in the same direction as the force. Energy, Work and Power Video

What is purpose of a machine? Device that allows you to do work easier

How do machines make work easier? They can change the amount of force They can change the distance They can also change the direction (Remember that Work = Force X Distance) Change in the size of the force changes the distance. No machine can increase both force and distance MORE

How do machines make work easier? May change: (W = F X d) Amount of force exerted (x force decreases distance the load moves) Distance over which you exert force (x the distance decreases force.) Direction in which you exert force (force and distance constant change the direction in which the load moves.

What is mechanical advantage? The number of times a machine increases a force exerted on it. M.A=output force/input force SO… increasing force: MA greater than 1 Increasing distance: MA less than 1 Changing direction: MA=a

Examples

What are the 3 types of simple machines? There are three simple machines: the lever, the pulley, and the inclined plane The wheel and axle, the wedge, and the screw are modifications of the three simple machines. Draw an example of each simple machine

Simple Machine Changes the size or direction of a force Does not increase the amount of work done

Inclined Plane Lever No moving parts Increases the distance over which an applied force acts Transfer effort Always turns on a fixed point : Fulcrum Effort arm: between fulcrum and point where force is applied Resistance arm: between fulcrum and load

Fulcrum at center of axle Resistance arm: radius of axle Wheel and Axle Pulley Fulcrum at center of axle Resistance arm: radius of axle Effort arm: radius of wheel Effort applied to wheel is transferred to axle Ex: doorknob, steering wheel Wheel turns as rope runs over it Can be fixed or move along rope Fixed: load hangs on one side and effort applied on other Moveable: load hangs on the rope

What is a compound (or complex) machine? A machine made up of two or more simple machines. Subsystems work together to perform a function Ex: bicycle, ballpoint pen

Rube Goldberg Extra Credit A Rube Goldberg machine is a overly complicated and laborious system that does a very simple job. This Too Shall Pass – Rube Goldberg Official Video To be credited for making the machine it must consist of a minimum of 16 individual steps earning 20 points or more depending on number of steps and complexity. Due Date: March 30, 2015 See me for a rubric https://sites.google.com/site/franchinaphysicalscience/extra-credit/rubegoldbergextracredit

Rube Goldberg Pager Turner Mousetrap to Mars Melvin the Magical Mixed Media Machine Mythbusters Rube Goldberg Contraption Honda – The Cog

Works Cited Notes were adapted from The Science Class web site at www.science-class.net and from Queensland Science Teachers at http://qldscienceteachers.tripod.com/junior/physics/work.html