Chapter 5.2 Physical Science WZPP ps Ok web post Using Machines Chapter 5.2 Physical Science WZPP ps Ok web post

What is a Machine? Something that makes work (force x distance) easier Does not need to be powered Can be powered by the force of a person

Making work easier Increasing the force applied to an object or You can do the same amount of work by applying a small force over a greater distance or a large force over a short distance See the jack example: figure 6, page 132

Making work easier Increasing the distance Work stays the same When you increase the distance, less force will be needed

Making work easier Changing Directions This can be to the sides or opposite direction

Work Done by Machines Two kinds of forces need to be considered when using machines Work I do on the machine (Win) Work done by the machine (Wout)

Conserving Energy Amount of energy put in the machine needs to be greater than the energy out of the machine This is real life Machines can not create energy Some energy is lost as friction

Ideal Machine Is a perfect machine No friction, no mass, no weight So Win = Wout (remember, F x D = W) (Effort Force x Effort Distance = Resistance force x resistance distance) Fe x De = Fr x Dr 5.2B ws

Mechanical Advantage (MA) Is the number of times a machine multiples an effort force Mechanical advantage = resistance force divided by the Effort force M A = Fr / Fe

Efficiency Is the measure of how much work put into a machine is changed into useful work by the machine High efficiency machines produce less heat from friction Efficiency is Wout / Win x 100%

Efficiency Efficiency of real machines is always less than 100% Machine can be made more efficient by reducing friction Add lubricant– oil, grease end notes 5.2 ps 5.2C ws