Work… DO WORK SON! work = force x distance W = Fd Units: Force = Newtons Distance = meters Work = Nm or a JOULE (J)
Work Problems • If he lifts 100kg 2.0 meters off the floor, then W = Fd =1000N x 2.0 m W = 2000 Joules 2. How many Joules of work is the convict doing? W = Fd W = F x 0 W = 0 Joules
Power • If a force of 50 N pushes an object 15 m in 5 seconds, how much power is done? • What is the unit of power…NO • WATT is the unit of power • A J/s is a W • There are also…kW and MW. And, 100 kW = 134 HP
Energy • The ability to do work • Types of Energy • Potential: Energy Stored • Gravitational Potential Energy: Energy Stored due to the force of gravity. • Chemical Energy: Energy stored or released in chemical bonds • Heat • Electromagnetic • Nuclear • Mass • Energy is in Joules
Examples of Potential Energy Gravitational PE Chemical PE How much GPE does the 10 kg ball have when its 3 m above the ground? GPE = F x d = mg x h = mgh = (10)(9.8)(3) = 300J GPE and work are both energy and are in Joules. Elastic PE
MOTION. The energy of Kinetic Energy p 105 KE = ½ mv2 What’s the energy of a 1000kg car moving at 20 m/s? KE = ½ mv2 = ½ (1000)(20)2 = 200,000J = 200kJ
Work-Energy Theorem p105 When you throw a ball, you give it energy of motion. Throw is workFd. Energy of motion is KE½ mv2. SO Fd = ½ m(Δv)2 Work = change in KE How much work does it take to accelerate a 500kg car from 25 m/s to 50 m/s? W = ∆KE = ½ m (∆ v)2 = ½ (500)(50-25)2 = 156kJ
Conservation of Energy p106 Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.