2. Work
• Work has a very specific meaning
• Work is done by forces on objects over a
distance
• Units for Work
• Joules or Newton-meter
Force (N)
W=Fxd
Work (Joules)
Distance (m)
3. Work Example
• If you push a box with a force of 5N for a distance
of 1m, how much Work have you done?
W = Fd
4. Work Input/Output
• Work input
– Work put into a system
– Force applied to a system
• Work output
– Work coming out of system
– Forces put out by a machine
• Work output never exceeds work input
– Machines lose energy through friction
5. Efficiency
• Written as a percent (%)
• Calculates how well a machine works
efficiency = Wo x 100
WI
6. Efficiency
• An ideal machine or “perfect machine” has no
energy lost
– Doesn’t exist!
• Most efficient machine is a bicycle (95%)
• Human body (8%)
7. Power
• Power is the rate (how fast/slow) work is done
• It makes a difference how fast (time) you do work
• 2 units of power
– Metric system
• Watts (J/s)
– English system
• Horsepower (746 watts)
• 1 horse = 1 horsepower
