Work and EnergyWork and Energy

EnergyEnergy

Kinetic EnergyKinetic EnergyKinetic energy – energy of an object Kinetic energy – energy of an object due to its motiondue to its motionKinetic energy depends on speed and Kinetic energy depends on speed and massmassKinetic energy = ½ * mass * (speed)Kinetic energy = ½ * mass * (speed)22

KE= ½mvKE= ½mv22

Energy is measured in Joules (J)Energy is measured in Joules (J)

Kinetic EnergyKinetic Energy

Work-Kinetic Energy TheoremWork-Kinetic Energy TheoremThe net work done on an object is The net work done on an object is equal to the change in the kinetic equal to the change in the kinetic energy of that objectenergy of that object

Net work = change in kinetic energyNet work = change in kinetic energy

WWnetnet==ΔΔKEKE

Work-Kinetic Energy TheoremWork-Kinetic Energy TheoremSpeed of the object and kinetic Speed of the object and kinetic energy increase if work is positiveenergy increase if work is positiveSpeed of the object and kinetic Speed of the object and kinetic energy decrease if work is negativeenergy decrease if work is negativeKinetic energy is the work an object Kinetic energy is the work an object can do as it comes to restcan do as it comes to restKinetic energy is the amount of Kinetic energy is the amount of energy stored in an objectenergy stored in an object

Potential EnergyPotential EnergyPotential energy – energy associated Potential energy – energy associated with an object due to the position of with an object due to the position of the objectthe object– Relative and is based on a frame of Relative and is based on a frame of

referencereference– Abbreviated PE or UAbbreviated PE or U– Measured in Joules (J)Measured in Joules (J)– Two main kinds of potential energyTwo main kinds of potential energy

Gravitational and elastic potential energiesGravitational and elastic potential energies

Gravitational Potential EnergyGravitational Potential EnergyGravitational potential energy (PEGravitational potential energy (PEgg) – ) – potential energy associated with an object potential energy associated with an object due to the position of the object relative to due to the position of the object relative to the Earth or some other gravitational the Earth or some other gravitational sourcesource– Based on height from a zero levelBased on height from a zero level– Gravitational potential energy = mass * free-fall Gravitational potential energy = mass * free-fall

acceleration * heightacceleration * height– PEPEgg=mgh=mgh– As objects fall gravitational potential energy is As objects fall gravitational potential energy is

converted to kinetic energyconverted to kinetic energy– At the zero level, the object no longer has any At the zero level, the object no longer has any

gravitational potential energygravitational potential energy

Gravitational Potential EnergyGravitational Potential Energy

Gravitational Potential EnergyGravitational Potential Energy

Elastic Potential EnergyElastic Potential EnergyElastic potential energy – the Elastic potential energy – the potential energy in a stretched or potential energy in a stretched or compressed elastic objectcompressed elastic object– Energy of springs and rubber bandsEnergy of springs and rubber bandsRelaxed length – the length of a Relaxed length – the length of a spring when no external forces are spring when no external forces are acting upon itacting upon it– As the spring is compressed, elastic As the spring is compressed, elastic

potential energy is stored in the springpotential energy is stored in the spring

Elastic Potential EnergyElastic Potential EnergySpring constant – a parameter that Spring constant – a parameter that expresses how resistant a spring is to expresses how resistant a spring is to being compressed or stretchedbeing compressed or stretched– Has units of Newtons / meters (N/m)Has units of Newtons / meters (N/m)Elastic potential energy = ½ * spring Elastic potential energy = ½ * spring constant * (distance compressed or constant * (distance compressed or stretched)stretched)22

PEPEelasticelastic= ½kx= ½kx22

Elastic Potential EnergyElastic Potential Energy