Unit 3 Energy, Work, and Power

Energy is the ability to do work Work occurs when an object moves in the direction of an applied force (or component) Power is the rate at which work is done

Types of energy 1)Potential (U) a)Gravitational b)Elastic 2)Kinetic (K) 3)Mechanical (E)

Work and potential energy Gravitational potential energy change – Raise or lower object – Requires force – Requires a distance – Work is done Elastic potential energy change – Compress or stretch a “spring” – Requires force – Requires a distance – Work is done

Work and kinetic energy Kinetic energy change – Increase or decrease speed – Acceleration – Acceleration requires force – Acceleration and/or speed means distance – Work is done

W = ΔU* W = ΔK* ΔU = ΔK* *Sometimes A change in energy means work is done Work does not mean a change in kinetic and/or potential energy

Nonconservative forces cause a change in the energy of the system Work may be done to overcome friction In the absence of nonconservative forces W = ΔK + ΔU Energy is conserved in the absence of nonconservative forces

Kinetic energy K = ½mv 2

Mechanical energy is kinetic plus potential E = K + U

h x θ

A pendulum with l = 3.7 m and m = 7.2 kg is released from the horizontal. Determine the tension in the string when it makes an angle θ = 25º with the vertical. θ mg T θ