Work in / Work out Work/Energy Principle

potential energy: STORED ENERGY –can be in a FIELD or DEVICE gravitational PE is stored in gravitational fields elastic PE is stored in elastic objects (springs) Definitions – Types of Energy

2.0 m 30 kg A 30 kilogram object is positioned 2.0 meters above the surface of the Earth. –What is the gravitational potential energy of the object? Example #1 – Gravitational PE ΔPE = mgΔh ΔPE = (30 kg)(9.81 m/s 2 )(2.0 m) ΔPE = J

The length of a spring with a spring constant of 100 newtons per meter is changed by 4.0 centimeters. –What is the elastic potential energy stored in the spring? Example #2 – Elastic PE PE S = ½ kx 2 PE S = ½ (100 N/m)(0.04 m) 2 PE S = 0.08 J 10 cm14 cm

kinetic energy: ENERGY OF MOVING OBJECTS –depends on mass and velocity Definitions – Types of Energy

A 5.0 kilogram toy car is moving at 2.0 meters per second. –What is the kinetic energy of the toy car? Example #3 – Kinetic Energy KE = ½ mv 2 KE = ½ (5.0 kg)(2.0 m/s) 2 KE = 10 J

internal energy: TEMPERATURE/HEAT Definitions – Types of Energy

When work is done ‘on a system’ there is a net gain of one or more types of energy by that system. Energy types can change within a system. Work/Energy Principle WORK Gravitational PE Elastic PE Kinetic Energy Internal Energy if “h” increases if “x” increases if “v” increases if temp. increases

Work/Energy Principle – Scenario #1 A car is moving along a flat surface with an increasing speed. What type(s) of energy are changing? PE g PE S KEQ XX↑?

A car is moving up an incline with constant speed. What type(s) of energy are changing? PE g PE S KEQ ↑XX? Work/Energy Principle – Scenario #2

A car is applying its brakes and slowing down as it moves down a slope. What type(s) of energy are changing? PE g PE S KEQ ↓X↓↑ Work/Energy Principle – Scenario #3

A cart is moving on a flat surface toward a wall and is stopped by a spring on its front. What type(s) of energy are changing? PE g PE S KEQ X↑↓? Work/Energy Principle – Scenario #4

A rocket flies upward with an increasing velocity [ignore air resistance]. What type(s) of energy are changing? PE g PE S KEQ ↑X↑X Work/Energy Principle – Scenario #5

End of PRACTICE