1. 5.2
Using Machines

2. What is a Machine? Machine: device that makes doing work easier. Knife
Scissor
Doorknob
Car engine

3. 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

4. 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

5. 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).

6. 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

7. 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

8. 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.