Work and Energy Flashcards
Types of Energy
• Unit is Joules (J): (kg • m²)/(s²)
• Kinetic Energy: K = ½mv²
• Gravitational Potential Energy: U = mgh
• Elastic Potential Energy: U = ½kx²
• Total Mechanical Energy: Sum of object’s potential and kinetic energies.
• E = U + K
• Conservative Forces: ΔE = ΔU + ΔK = 0.
• Nonconservative Forces: Wₙ = ΔE = ΔU + ΔK.
• Nonconservative forces account for energy lost from a system due to friction or heat.
Work
• Work: Measure of energy transfer.
• W = F × d × cos(θ).
• In gas systems, work is represented by area under P-V graph. Volume on x-axis and pressure on y-axis.
• When gas expands, force is exerted against a piston, causing the volume of the system to increase; work is positive.
• When gas is compressed, force is exerted by the piston to decrease the volume of the system; work is negative.
• Isovolumetric (Isochoric) Process: Volume stays constant as pressure changes; ΔV = 0, then W = 0.
• Isobaric Process: Pressure stays constant as volume changes; W = PΔV.
• Power (Watt): Rate of energy transfer from one system to another; P = W/t = ΔE/t.
• Work-Energy Theorem: Direct relationship between the work done by all the forces acting on an object and the change in kinetic energy of that object; Wₙ = ΔK.
Mechanical Advantage
• Mechanical Advantage = F(out)/F(in).
• Inclined planes and pulleys.
• Allows same amount of work to be accomplished by decreasing input force by some factor and by increasing distance through which the force is applied by same factor.
