Presentation on theme: "5.2 Using Machines. What is a Machine? Machine: device that makes doing work easier. – Knife – Scissor – Doorknob – Car engine."— Presentation transcript:
5.2 Using Machines
What is a Machine? Machine: device that makes doing work easier. – Knife – Scissor – Doorknob – Car engine
Making work easier Machines make work easier by: – increasing the force that can be applied to an object. Car Jack allows you to lift car – Increasing the distance over which a force can be applied. Ramps – Changing the direction of an applied force. Pull down on cord for blinds Amount of work does not change
Work done by Machines Crowbar – when you do work on the machine (crowbar), it does work on the lid. 2 Forces involved: – Effort force: force applied to the machine – Resistance force: force applied by the machine 2 types of Work: – Input work: Work done by you on a machine – Output work: Work done by the machine
Conserving Energy When you do work on a machine, you transfer energy to the machine. The work you get out of a machine can never be more than what you put into the machine. Actually some energy is always lost to friction so W(out) is always less than W(in).
Ideal Machines W(in) = W(out) Fe X de = Fr X dr – Fe = Force effort (what you exert) – Fr = Force resistance (what you are moving) – De = Distance effort – Dr = Distance resistance – Hammer example
Mechanical Advantage The number of times a machine multiplies the effort force. MA = Fr Fe * When only the direction of force changes, the MA = 1
Efficiency A measure of how much of the work you put into a machine is changed to useful output work by the machine. Eff = Wout X100% Win Efficiency is always less than 100% **Increase efficiency by decreasing friction.