2 The ability of a physical system to cause change What is Energy?The ability of a physical system to cause changeWhat is its definition?Energy can come in many forms and is transferrable. It is a conserved quantity in the universe.What are its properties?Chemical, electrical, nuclear, thermodynamic, light, mechanical, kinetic, potential, elastic, etc.What forms can it be in?
4 Work (Energy) is a scalar quantity. What is Work?The amount of energy transferred by a force acting through a displacementWhat is its definition?Work (Energy) is a scalar quantity.What are its properties?How can it be calculated?W=fscosθ
10 Work-Energy TheoremThe work done by a net force in displacing a particle equals the change in kinetic energy of the particle. Stress on the word particle. This is a drastic idealization.
11 Mechanical Potential Energy GravitationalElastic
12 Conservation of Energy This is always true, but mechanical energy is only conserved when only conservative forces are present.Work done by a conservative force is path independentForces such as friction and air drag are non-conservative. They result in energy dissipated as heat.
14 Power The time rate at which work is being done. How do we calculate it?If a net force acts on a particle and does work W over an interval of time Δt, then the average power is:
15 PowerThe time rate of energy transfer.Instantaneous Power
16 Power Watt are the units? 1hp=550ft*lbs/sec=746W Note: A kilowatt-hour is often used by power companies. What is it a measure of?
17 Potential Energy and Conservative Forces Potential energy is only associated with conservative forces. If an object or field does work on some external object, energy is transferred from the object or field to the external object:The energy transferred as work decreases the potential energy of the system from which it came.
18 Potential Energy and Conservative Forces The conservative force equals the negative (partial) derivative of the potential energy with respect to x.The negative sign means that the final potential energy of the system is lower than the initial as the conservative force does work.
19 Potential Energy and Conservative Forces Examples: